A moderate set of locking updates:
- A few extensions to the rwsem API and support for opportunistic
spinning and lock stealing
- lockdep selftest improvements
- Documentation updates
- Cleanups and small fixes all over the place
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Merge tag 'locking-core-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Thomas Gleixner:
"A moderate set of locking updates:
- A few extensions to the rwsem API and support for opportunistic
spinning and lock stealing
- lockdep selftest improvements
- Documentation updates
- Cleanups and small fixes all over the place"
* tag 'locking-core-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (21 commits)
seqlock: kernel-doc: Specify when preemption is automatically altered
seqlock: Prefix internal seqcount_t-only macros with a "do_"
Documentation: seqlock: s/LOCKTYPE/LOCKNAME/g
locking/rwsem: Remove reader optimistic spinning
locking/rwsem: Enable reader optimistic lock stealing
locking/rwsem: Prevent potential lock starvation
locking/rwsem: Pass the current atomic count to rwsem_down_read_slowpath()
locking/rwsem: Fold __down_{read,write}*()
locking/rwsem: Introduce rwsem_write_trylock()
locking/rwsem: Better collate rwsem_read_trylock()
rwsem: Implement down_read_interruptible
rwsem: Implement down_read_killable_nested
refcount: Fix a kernel-doc markup
completion: Drop init_completion define
atomic: Update MAINTAINERS
atomic: Delete obsolete documentation
seqlock: Rename __seqprop() users
lockdep/selftest: Add spin_nest_lock test
lockdep/selftests: Fix PROVE_RAW_LOCK_NESTING
seqlock: avoid -Wshadow warnings
...
This commit is contained in:
Linus Torvalds
commit
e857b6fcc5
|
|
@ -1,664 +0,0 @@
|
|||
=======================================================
|
||||
Semantics and Behavior of Atomic and Bitmask Operations
|
||||
=======================================================
|
||||
|
||||
:Author: David S. Miller
|
||||
|
||||
This document is intended to serve as a guide to Linux port
|
||||
maintainers on how to implement atomic counter, bitops, and spinlock
|
||||
interfaces properly.
|
||||
|
||||
Atomic Type And Operations
|
||||
==========================
|
||||
|
||||
The atomic_t type should be defined as a signed integer and
|
||||
the atomic_long_t type as a signed long integer. Also, they should
|
||||
be made opaque such that any kind of cast to a normal C integer type
|
||||
will fail. Something like the following should suffice::
|
||||
|
||||
typedef struct { int counter; } atomic_t;
|
||||
typedef struct { long counter; } atomic_long_t;
|
||||
|
||||
Historically, counter has been declared volatile. This is now discouraged.
|
||||
See :ref:`Documentation/process/volatile-considered-harmful.rst
|
||||
<volatile_considered_harmful>` for the complete rationale.
|
||||
|
||||
local_t is very similar to atomic_t. If the counter is per CPU and only
|
||||
updated by one CPU, local_t is probably more appropriate. Please see
|
||||
:ref:`Documentation/core-api/local_ops.rst <local_ops>` for the semantics of
|
||||
local_t.
|
||||
|
||||
The first operations to implement for atomic_t's are the initializers and
|
||||
plain writes. ::
|
||||
|
||||
#define ATOMIC_INIT(i) { (i) }
|
||||
#define atomic_set(v, i) ((v)->counter = (i))
|
||||
|
||||
The first macro is used in definitions, such as::
|
||||
|
||||
static atomic_t my_counter = ATOMIC_INIT(1);
|
||||
|
||||
The initializer is atomic in that the return values of the atomic operations
|
||||
are guaranteed to be correct reflecting the initialized value if the
|
||||
initializer is used before runtime. If the initializer is used at runtime, a
|
||||
proper implicit or explicit read memory barrier is needed before reading the
|
||||
value with atomic_read from another thread.
|
||||
|
||||
As with all of the ``atomic_`` interfaces, replace the leading ``atomic_``
|
||||
with ``atomic_long_`` to operate on atomic_long_t.
|
||||
|
||||
The second interface can be used at runtime, as in::
|
||||
|
||||
struct foo { atomic_t counter; };
|
||||
...
|
||||
|
||||
struct foo *k;
|
||||
|
||||
k = kmalloc(sizeof(*k), GFP_KERNEL);
|
||||
if (!k)
|
||||
return -ENOMEM;
|
||||
atomic_set(&k->counter, 0);
|
||||
|
||||
The setting is atomic in that the return values of the atomic operations by
|
||||
all threads are guaranteed to be correct reflecting either the value that has
|
||||
been set with this operation or set with another operation. A proper implicit
|
||||
or explicit memory barrier is needed before the value set with the operation
|
||||
is guaranteed to be readable with atomic_read from another thread.
|
||||
|
||||
Next, we have::
|
||||
|
||||
#define atomic_read(v) ((v)->counter)
|
||||
|
||||
which simply reads the counter value currently visible to the calling thread.
|
||||
The read is atomic in that the return value is guaranteed to be one of the
|
||||
values initialized or modified with the interface operations if a proper
|
||||
implicit or explicit memory barrier is used after possible runtime
|
||||
initialization by any other thread and the value is modified only with the
|
||||
interface operations. atomic_read does not guarantee that the runtime
|
||||
initialization by any other thread is visible yet, so the user of the
|
||||
interface must take care of that with a proper implicit or explicit memory
|
||||
barrier.
|
||||
|
||||
.. warning::
|
||||
|
||||
``atomic_read()`` and ``atomic_set()`` DO NOT IMPLY BARRIERS!
|
||||
|
||||
Some architectures may choose to use the volatile keyword, barriers, or
|
||||
inline assembly to guarantee some degree of immediacy for atomic_read()
|
||||
and atomic_set(). This is not uniformly guaranteed, and may change in
|
||||
the future, so all users of atomic_t should treat atomic_read() and
|
||||
atomic_set() as simple C statements that may be reordered or optimized
|
||||
away entirely by the compiler or processor, and explicitly invoke the
|
||||
appropriate compiler and/or memory barrier for each use case. Failure
|
||||
to do so will result in code that may suddenly break when used with
|
||||
different architectures or compiler optimizations, or even changes in
|
||||
unrelated code which changes how the compiler optimizes the section
|
||||
accessing atomic_t variables.
|
||||
|
||||
Properly aligned pointers, longs, ints, and chars (and unsigned
|
||||
equivalents) may be atomically loaded from and stored to in the same
|
||||
sense as described for atomic_read() and atomic_set(). The READ_ONCE()
|
||||
and WRITE_ONCE() macros should be used to prevent the compiler from using
|
||||
optimizations that might otherwise optimize accesses out of existence on
|
||||
the one hand, or that might create unsolicited accesses on the other.
|
||||
|
||||
For example consider the following code::
|
||||
|
||||
while (a > 0)
|
||||
do_something();
|
||||
|
||||
If the compiler can prove that do_something() does not store to the
|
||||
variable a, then the compiler is within its rights transforming this to
|
||||
the following::
|
||||
|
||||
if (a > 0)
|
||||
for (;;)
|
||||
do_something();
|
||||
|
||||
If you don't want the compiler to do this (and you probably don't), then
|
||||
you should use something like the following::
|
||||
|
||||
while (READ_ONCE(a) > 0)
|
||||
do_something();
|
||||
|
||||
Alternatively, you could place a barrier() call in the loop.
|
||||
|
||||
For another example, consider the following code::
|
||||
|
||||
tmp_a = a;
|
||||
do_something_with(tmp_a);
|
||||
do_something_else_with(tmp_a);
|
||||
|
||||
If the compiler can prove that do_something_with() does not store to the
|
||||
variable a, then the compiler is within its rights to manufacture an
|
||||
additional load as follows::
|
||||
|
||||
tmp_a = a;
|
||||
do_something_with(tmp_a);
|
||||
tmp_a = a;
|
||||
do_something_else_with(tmp_a);
|
||||
|
||||
This could fatally confuse your code if it expected the same value
|
||||
to be passed to do_something_with() and do_something_else_with().
|
||||
|
||||
The compiler would be likely to manufacture this additional load if
|
||||
do_something_with() was an inline function that made very heavy use
|
||||
of registers: reloading from variable a could save a flush to the
|
||||
stack and later reload. To prevent the compiler from attacking your
|
||||
code in this manner, write the following::
|
||||
|
||||
tmp_a = READ_ONCE(a);
|
||||
do_something_with(tmp_a);
|
||||
do_something_else_with(tmp_a);
|
||||
|
||||
For a final example, consider the following code, assuming that the
|
||||
variable a is set at boot time before the second CPU is brought online
|
||||
and never changed later, so that memory barriers are not needed::
|
||||
|
||||
if (a)
|
||||
b = 9;
|
||||
else
|
||||
b = 42;
|
||||
|
||||
The compiler is within its rights to manufacture an additional store
|
||||
by transforming the above code into the following::
|
||||
|
||||
b = 42;
|
||||
if (a)
|
||||
b = 9;
|
||||
|
||||
This could come as a fatal surprise to other code running concurrently
|
||||
that expected b to never have the value 42 if a was zero. To prevent
|
||||
the compiler from doing this, write something like::
|
||||
|
||||
if (a)
|
||||
WRITE_ONCE(b, 9);
|
||||
else
|
||||
WRITE_ONCE(b, 42);
|
||||
|
||||
Don't even -think- about doing this without proper use of memory barriers,
|
||||
locks, or atomic operations if variable a can change at runtime!
|
||||
|
||||
.. warning::
|
||||
|
||||
``READ_ONCE()`` OR ``WRITE_ONCE()`` DO NOT IMPLY A BARRIER!
|
||||
|
||||
Now, we move onto the atomic operation interfaces typically implemented with
|
||||
the help of assembly code. ::
|
||||
|
||||
void atomic_add(int i, atomic_t *v);
|
||||
void atomic_sub(int i, atomic_t *v);
|
||||
void atomic_inc(atomic_t *v);
|
||||
void atomic_dec(atomic_t *v);
|
||||
|
||||
These four routines add and subtract integral values to/from the given
|
||||
atomic_t value. The first two routines pass explicit integers by
|
||||
which to make the adjustment, whereas the latter two use an implicit
|
||||
adjustment value of "1".
|
||||
|
||||
One very important aspect of these two routines is that they DO NOT
|
||||
require any explicit memory barriers. They need only perform the
|
||||
atomic_t counter update in an SMP safe manner.
|
||||
|
||||
Next, we have::
|
||||
|
||||
int atomic_inc_return(atomic_t *v);
|
||||
int atomic_dec_return(atomic_t *v);
|
||||
|
||||
These routines add 1 and subtract 1, respectively, from the given
|
||||
atomic_t and return the new counter value after the operation is
|
||||
performed.
|
||||
|
||||
Unlike the above routines, it is required that these primitives
|
||||
include explicit memory barriers that are performed before and after
|
||||
the operation. It must be done such that all memory operations before
|
||||
and after the atomic operation calls are strongly ordered with respect
|
||||
to the atomic operation itself.
|
||||
|
||||
For example, it should behave as if a smp_mb() call existed both
|
||||
before and after the atomic operation.
|
||||
|
||||
If the atomic instructions used in an implementation provide explicit
|
||||
memory barrier semantics which satisfy the above requirements, that is
|
||||
fine as well.
|
||||
|
||||
Let's move on::
|
||||
|
||||
int atomic_add_return(int i, atomic_t *v);
|
||||
int atomic_sub_return(int i, atomic_t *v);
|
||||
|
||||
These behave just like atomic_{inc,dec}_return() except that an
|
||||
explicit counter adjustment is given instead of the implicit "1".
|
||||
This means that like atomic_{inc,dec}_return(), the memory barrier
|
||||
semantics are required.
|
||||
|
||||
Next::
|
||||
|
||||
int atomic_inc_and_test(atomic_t *v);
|
||||
int atomic_dec_and_test(atomic_t *v);
|
||||
|
||||
These two routines increment and decrement by 1, respectively, the
|
||||
given atomic counter. They return a boolean indicating whether the
|
||||
resulting counter value was zero or not.
|
||||
|
||||
Again, these primitives provide explicit memory barrier semantics around
|
||||
the atomic operation::
|
||||
|
||||
int atomic_sub_and_test(int i, atomic_t *v);
|
||||
|
||||
This is identical to atomic_dec_and_test() except that an explicit
|
||||
decrement is given instead of the implicit "1". This primitive must
|
||||
provide explicit memory barrier semantics around the operation::
|
||||
|
||||
int atomic_add_negative(int i, atomic_t *v);
|
||||
|
||||
The given increment is added to the given atomic counter value. A boolean
|
||||
is return which indicates whether the resulting counter value is negative.
|
||||
This primitive must provide explicit memory barrier semantics around
|
||||
the operation.
|
||||
|
||||
Then::
|
||||
|
||||
int atomic_xchg(atomic_t *v, int new);
|
||||
|
||||
This performs an atomic exchange operation on the atomic variable v, setting
|
||||
the given new value. It returns the old value that the atomic variable v had
|
||||
just before the operation.
|
||||
|
||||
atomic_xchg must provide explicit memory barriers around the operation. ::
|
||||
|
||||
int atomic_cmpxchg(atomic_t *v, int old, int new);
|
||||
|
||||
This performs an atomic compare exchange operation on the atomic value v,
|
||||
with the given old and new values. Like all atomic_xxx operations,
|
||||
atomic_cmpxchg will only satisfy its atomicity semantics as long as all
|
||||
other accesses of \*v are performed through atomic_xxx operations.
|
||||
|
||||
atomic_cmpxchg must provide explicit memory barriers around the operation,
|
||||
although if the comparison fails then no memory ordering guarantees are
|
||||
required.
|
||||
|
||||
The semantics for atomic_cmpxchg are the same as those defined for 'cas'
|
||||
below.
|
||||
|
||||
Finally::
|
||||
|
||||
int atomic_add_unless(atomic_t *v, int a, int u);
|
||||
|
||||
If the atomic value v is not equal to u, this function adds a to v, and
|
||||
returns non zero. If v is equal to u then it returns zero. This is done as
|
||||
an atomic operation.
|
||||
|
||||
atomic_add_unless must provide explicit memory barriers around the
|
||||
operation unless it fails (returns 0).
|
||||
|
||||
atomic_inc_not_zero, equivalent to atomic_add_unless(v, 1, 0)
|
||||
|
||||
|
||||
If a caller requires memory barrier semantics around an atomic_t
|
||||
operation which does not return a value, a set of interfaces are
|
||||
defined which accomplish this::
|
||||
|
||||
void smp_mb__before_atomic(void);
|
||||
void smp_mb__after_atomic(void);
|
||||
|
||||
Preceding a non-value-returning read-modify-write atomic operation with
|
||||
smp_mb__before_atomic() and following it with smp_mb__after_atomic()
|
||||
provides the same full ordering that is provided by value-returning
|
||||
read-modify-write atomic operations.
|
||||
|
||||
For example, smp_mb__before_atomic() can be used like so::
|
||||
|
||||
obj->dead = 1;
|
||||
smp_mb__before_atomic();
|
||||
atomic_dec(&obj->ref_count);
|
||||
|
||||
It makes sure that all memory operations preceding the atomic_dec()
|
||||
call are strongly ordered with respect to the atomic counter
|
||||
operation. In the above example, it guarantees that the assignment of
|
||||
"1" to obj->dead will be globally visible to other cpus before the
|
||||
atomic counter decrement.
|
||||
|
||||
Without the explicit smp_mb__before_atomic() call, the
|
||||
implementation could legally allow the atomic counter update visible
|
||||
to other cpus before the "obj->dead = 1;" assignment.
|
||||
|
||||
A missing memory barrier in the cases where they are required by the
|
||||
atomic_t implementation above can have disastrous results. Here is
|
||||
an example, which follows a pattern occurring frequently in the Linux
|
||||
kernel. It is the use of atomic counters to implement reference
|
||||
counting, and it works such that once the counter falls to zero it can
|
||||
be guaranteed that no other entity can be accessing the object::
|
||||
|
||||
static void obj_list_add(struct obj *obj, struct list_head *head)
|
||||
{
|
||||
obj->active = 1;
|
||||
list_add(&obj->list, head);
|
||||
}
|
||||
|
||||
static void obj_list_del(struct obj *obj)
|
||||
{
|
||||
list_del(&obj->list);
|
||||
obj->active = 0;
|
||||
}
|
||||
|
||||
static void obj_destroy(struct obj *obj)
|
||||
{
|
||||
BUG_ON(obj->active);
|
||||
kfree(obj);
|
||||
}
|
||||
|
||||
struct obj *obj_list_peek(struct list_head *head)
|
||||
{
|
||||
if (!list_empty(head)) {
|
||||
struct obj *obj;
|
||||
|
||||
obj = list_entry(head->next, struct obj, list);
|
||||
atomic_inc(&obj->refcnt);
|
||||
return obj;
|
||||
}
|
||||
return NULL;
|
||||
}
|
||||
|
||||
void obj_poke(void)
|
||||
{
|
||||
struct obj *obj;
|
||||
|
||||
spin_lock(&global_list_lock);
|
||||
obj = obj_list_peek(&global_list);
|
||||
spin_unlock(&global_list_lock);
|
||||
|
||||
if (obj) {
|
||||
obj->ops->poke(obj);
|
||||
if (atomic_dec_and_test(&obj->refcnt))
|
||||
obj_destroy(obj);
|
||||
}
|
||||
}
|
||||
|
||||
void obj_timeout(struct obj *obj)
|
||||
{
|
||||
spin_lock(&global_list_lock);
|
||||
obj_list_del(obj);
|
||||
spin_unlock(&global_list_lock);
|
||||
|
||||
if (atomic_dec_and_test(&obj->refcnt))
|
||||
obj_destroy(obj);
|
||||
}
|
||||
|
||||
.. note::
|
||||
|
||||
This is a simplification of the ARP queue management in the generic
|
||||
neighbour discover code of the networking. Olaf Kirch found a bug wrt.
|
||||
memory barriers in kfree_skb() that exposed the atomic_t memory barrier
|
||||
requirements quite clearly.
|
||||
|
||||
Given the above scheme, it must be the case that the obj->active
|
||||
update done by the obj list deletion be visible to other processors
|
||||
before the atomic counter decrement is performed.
|
||||
|
||||
Otherwise, the counter could fall to zero, yet obj->active would still
|
||||
be set, thus triggering the assertion in obj_destroy(). The error
|
||||
sequence looks like this::
|
||||
|
||||
cpu 0 cpu 1
|
||||
obj_poke() obj_timeout()
|
||||
obj = obj_list_peek();
|
||||
... gains ref to obj, refcnt=2
|
||||
obj_list_del(obj);
|
||||
obj->active = 0 ...
|
||||
... visibility delayed ...
|
||||
atomic_dec_and_test()
|
||||
... refcnt drops to 1 ...
|
||||
atomic_dec_and_test()
|
||||
... refcount drops to 0 ...
|
||||
obj_destroy()
|
||||
BUG() triggers since obj->active
|
||||
still seen as one
|
||||
obj->active update visibility occurs
|
||||
|
||||
With the memory barrier semantics required of the atomic_t operations
|
||||
which return values, the above sequence of memory visibility can never
|
||||
happen. Specifically, in the above case the atomic_dec_and_test()
|
||||
counter decrement would not become globally visible until the
|
||||
obj->active update does.
|
||||
|
||||
As a historical note, 32-bit Sparc used to only allow usage of
|
||||
24-bits of its atomic_t type. This was because it used 8 bits
|
||||
as a spinlock for SMP safety. Sparc32 lacked a "compare and swap"
|
||||
type instruction. However, 32-bit Sparc has since been moved over
|
||||
to a "hash table of spinlocks" scheme, that allows the full 32-bit
|
||||
counter to be realized. Essentially, an array of spinlocks are
|
||||
indexed into based upon the address of the atomic_t being operated
|
||||
on, and that lock protects the atomic operation. Parisc uses the
|
||||
same scheme.
|
||||
|
||||
Another note is that the atomic_t operations returning values are
|
||||
extremely slow on an old 386.
|
||||
|
||||
|
||||
Atomic Bitmask
|
||||
==============
|
||||
|
||||
We will now cover the atomic bitmask operations. You will find that
|
||||
their SMP and memory barrier semantics are similar in shape and scope
|
||||
to the atomic_t ops above.
|
||||
|
||||
Native atomic bit operations are defined to operate on objects aligned
|
||||
to the size of an "unsigned long" C data type, and are least of that
|
||||
size. The endianness of the bits within each "unsigned long" are the
|
||||
native endianness of the cpu. ::
|
||||
|
||||
void set_bit(unsigned long nr, volatile unsigned long *addr);
|
||||
void clear_bit(unsigned long nr, volatile unsigned long *addr);
|
||||
void change_bit(unsigned long nr, volatile unsigned long *addr);
|
||||
|
||||
These routines set, clear, and change, respectively, the bit number
|
||||
indicated by "nr" on the bit mask pointed to by "ADDR".
|
||||
|
||||
They must execute atomically, yet there are no implicit memory barrier
|
||||
semantics required of these interfaces. ::
|
||||
|
||||
int test_and_set_bit(unsigned long nr, volatile unsigned long *addr);
|
||||
int test_and_clear_bit(unsigned long nr, volatile unsigned long *addr);
|
||||
int test_and_change_bit(unsigned long nr, volatile unsigned long *addr);
|
||||
|
||||
Like the above, except that these routines return a boolean which
|
||||
indicates whether the changed bit was set _BEFORE_ the atomic bit
|
||||
operation.
|
||||
|
||||
|
||||
.. warning::
|
||||
It is incredibly important that the value be a boolean, ie. "0" or "1".
|
||||
Do not try to be fancy and save a few instructions by declaring the
|
||||
above to return "long" and just returning something like "old_val &
|
||||
mask" because that will not work.
|
||||
|
||||
For one thing, this return value gets truncated to int in many code
|
||||
paths using these interfaces, so on 64-bit if the bit is set in the
|
||||
upper 32-bits then testers will never see that.
|
||||
|
||||
One great example of where this problem crops up are the thread_info
|
||||
flag operations. Routines such as test_and_set_ti_thread_flag() chop
|
||||
the return value into an int. There are other places where things
|
||||
like this occur as well.
|
||||
|
||||
These routines, like the atomic_t counter operations returning values,
|
||||
must provide explicit memory barrier semantics around their execution.
|
||||
All memory operations before the atomic bit operation call must be
|
||||
made visible globally before the atomic bit operation is made visible.
|
||||
Likewise, the atomic bit operation must be visible globally before any
|
||||
subsequent memory operation is made visible. For example::
|
||||
|
||||
obj->dead = 1;
|
||||
if (test_and_set_bit(0, &obj->flags))
|
||||
/* ... */;
|
||||
obj->killed = 1;
|
||||
|
||||
The implementation of test_and_set_bit() must guarantee that
|
||||
"obj->dead = 1;" is visible to cpus before the atomic memory operation
|
||||
done by test_and_set_bit() becomes visible. Likewise, the atomic
|
||||
memory operation done by test_and_set_bit() must become visible before
|
||||
"obj->killed = 1;" is visible.
|
||||
|
||||
Finally there is the basic operation::
|
||||
|
||||
int test_bit(unsigned long nr, __const__ volatile unsigned long *addr);
|
||||
|
||||
Which returns a boolean indicating if bit "nr" is set in the bitmask
|
||||
pointed to by "addr".
|
||||
|
||||
If explicit memory barriers are required around {set,clear}_bit() (which do
|
||||
not return a value, and thus does not need to provide memory barrier
|
||||
semantics), two interfaces are provided::
|
||||
|
||||
void smp_mb__before_atomic(void);
|
||||
void smp_mb__after_atomic(void);
|
||||
|
||||
They are used as follows, and are akin to their atomic_t operation
|
||||
brothers::
|
||||
|
||||
/* All memory operations before this call will
|
||||
* be globally visible before the clear_bit().
|
||||
*/
|
||||
smp_mb__before_atomic();
|
||||
clear_bit( ... );
|
||||
|
||||
/* The clear_bit() will be visible before all
|
||||
* subsequent memory operations.
|
||||
*/
|
||||
smp_mb__after_atomic();
|
||||
|
||||
There are two special bitops with lock barrier semantics (acquire/release,
|
||||
same as spinlocks). These operate in the same way as their non-_lock/unlock
|
||||
postfixed variants, except that they are to provide acquire/release semantics,
|
||||
respectively. This means they can be used for bit_spin_trylock and
|
||||
bit_spin_unlock type operations without specifying any more barriers. ::
|
||||
|
||||
int test_and_set_bit_lock(unsigned long nr, unsigned long *addr);
|
||||
void clear_bit_unlock(unsigned long nr, unsigned long *addr);
|
||||
void __clear_bit_unlock(unsigned long nr, unsigned long *addr);
|
||||
|
||||
The __clear_bit_unlock version is non-atomic, however it still implements
|
||||
unlock barrier semantics. This can be useful if the lock itself is protecting
|
||||
the other bits in the word.
|
||||
|
||||
Finally, there are non-atomic versions of the bitmask operations
|
||||
provided. They are used in contexts where some other higher-level SMP
|
||||
locking scheme is being used to protect the bitmask, and thus less
|
||||
expensive non-atomic operations may be used in the implementation.
|
||||
They have names similar to the above bitmask operation interfaces,
|
||||
except that two underscores are prefixed to the interface name. ::
|
||||
|
||||
void __set_bit(unsigned long nr, volatile unsigned long *addr);
|
||||
void __clear_bit(unsigned long nr, volatile unsigned long *addr);
|
||||
void __change_bit(unsigned long nr, volatile unsigned long *addr);
|
||||
int __test_and_set_bit(unsigned long nr, volatile unsigned long *addr);
|
||||
int __test_and_clear_bit(unsigned long nr, volatile unsigned long *addr);
|
||||
int __test_and_change_bit(unsigned long nr, volatile unsigned long *addr);
|
||||
|
||||
These non-atomic variants also do not require any special memory
|
||||
barrier semantics.
|
||||
|
||||
The routines xchg() and cmpxchg() must provide the same exact
|
||||
memory-barrier semantics as the atomic and bit operations returning
|
||||
values.
|
||||
|
||||
.. note::
|
||||
|
||||
If someone wants to use xchg(), cmpxchg() and their variants,
|
||||
linux/atomic.h should be included rather than asm/cmpxchg.h, unless the
|
||||
code is in arch/* and can take care of itself.
|
||||
|
||||
Spinlocks and rwlocks have memory barrier expectations as well.
|
||||
The rule to follow is simple:
|
||||
|
||||
1) When acquiring a lock, the implementation must make it globally
|
||||
visible before any subsequent memory operation.
|
||||
|
||||
2) When releasing a lock, the implementation must make it such that
|
||||
all previous memory operations are globally visible before the
|
||||
lock release.
|
||||
|
||||
Which finally brings us to _atomic_dec_and_lock(). There is an
|
||||
architecture-neutral version implemented in lib/dec_and_lock.c,
|
||||
but most platforms will wish to optimize this in assembler. ::
|
||||
|
||||
int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock);
|
||||
|
||||
Atomically decrement the given counter, and if will drop to zero
|
||||
atomically acquire the given spinlock and perform the decrement
|
||||
of the counter to zero. If it does not drop to zero, do nothing
|
||||
with the spinlock.
|
||||
|
||||
It is actually pretty simple to get the memory barrier correct.
|
||||
Simply satisfy the spinlock grab requirements, which is make
|
||||
sure the spinlock operation is globally visible before any
|
||||
subsequent memory operation.
|
||||
|
||||
We can demonstrate this operation more clearly if we define
|
||||
an abstract atomic operation::
|
||||
|
||||
long cas(long *mem, long old, long new);
|
||||
|
||||
"cas" stands for "compare and swap". It atomically:
|
||||
|
||||
1) Compares "old" with the value currently at "mem".
|
||||
2) If they are equal, "new" is written to "mem".
|
||||
3) Regardless, the current value at "mem" is returned.
|
||||
|
||||
As an example usage, here is what an atomic counter update
|
||||
might look like::
|
||||
|
||||
void example_atomic_inc(long *counter)
|
||||
{
|
||||
long old, new, ret;
|
||||
|
||||
while (1) {
|
||||
old = *counter;
|
||||
new = old + 1;
|
||||
|
||||
ret = cas(counter, old, new);
|
||||
if (ret == old)
|
||||
break;
|
||||
}
|
||||
}
|
||||
|
||||
Let's use cas() in order to build a pseudo-C atomic_dec_and_lock()::
|
||||
|
||||
int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
|
||||
{
|
||||
long old, new, ret;
|
||||
int went_to_zero;
|
||||
|
||||
went_to_zero = 0;
|
||||
while (1) {
|
||||
old = atomic_read(atomic);
|
||||
new = old - 1;
|
||||
if (new == 0) {
|
||||
went_to_zero = 1;
|
||||
spin_lock(lock);
|
||||
}
|
||||
ret = cas(atomic, old, new);
|
||||
if (ret == old)
|
||||
break;
|
||||
if (went_to_zero) {
|
||||
spin_unlock(lock);
|
||||
went_to_zero = 0;
|
||||
}
|
||||
}
|
||||
|
||||
return went_to_zero;
|
||||
}
|
||||
|
||||
Now, as far as memory barriers go, as long as spin_lock()
|
||||
strictly orders all subsequent memory operations (including
|
||||
the cas()) with respect to itself, things will be fine.
|
||||
|
||||
Said another way, _atomic_dec_and_lock() must guarantee that
|
||||
a counter dropping to zero is never made visible before the
|
||||
spinlock being acquired.
|
||||
|
||||
.. note::
|
||||
|
||||
Note that this also means that for the case where the counter is not
|
||||
dropping to zero, there are no memory ordering requirements.
|
||||
|
|
@ -89,7 +89,7 @@ Read path::
|
|||
|
||||
.. _seqcount_locktype_t:
|
||||
|
||||
Sequence counters with associated locks (``seqcount_LOCKTYPE_t``)
|
||||
Sequence counters with associated locks (``seqcount_LOCKNAME_t``)
|
||||
-----------------------------------------------------------------
|
||||
|
||||
As discussed at :ref:`seqcount_t`, sequence count write side critical
|
||||
|
|
@ -115,27 +115,26 @@ The following sequence counters with associated locks are defined:
|
|||
- ``seqcount_mutex_t``
|
||||
- ``seqcount_ww_mutex_t``
|
||||
|
||||
The plain seqcount read and write APIs branch out to the specific
|
||||
seqcount_LOCKTYPE_t implementation at compile-time. This avoids kernel
|
||||
API explosion per each new seqcount LOCKTYPE.
|
||||
The sequence counter read and write APIs can take either a plain
|
||||
seqcount_t or any of the seqcount_LOCKNAME_t variants above.
|
||||
|
||||
Initialization (replace "LOCKTYPE" with one of the supported locks)::
|
||||
Initialization (replace "LOCKNAME" with one of the supported locks)::
|
||||
|
||||
/* dynamic */
|
||||
seqcount_LOCKTYPE_t foo_seqcount;
|
||||
seqcount_LOCKTYPE_init(&foo_seqcount, &lock);
|
||||
seqcount_LOCKNAME_t foo_seqcount;
|
||||
seqcount_LOCKNAME_init(&foo_seqcount, &lock);
|
||||
|
||||
/* static */
|
||||
static seqcount_LOCKTYPE_t foo_seqcount =
|
||||
SEQCNT_LOCKTYPE_ZERO(foo_seqcount, &lock);
|
||||
static seqcount_LOCKNAME_t foo_seqcount =
|
||||
SEQCNT_LOCKNAME_ZERO(foo_seqcount, &lock);
|
||||
|
||||
/* C99 struct init */
|
||||
struct {
|
||||
.seq = SEQCNT_LOCKTYPE_ZERO(foo.seq, &lock),
|
||||
.seq = SEQCNT_LOCKNAME_ZERO(foo.seq, &lock),
|
||||
} foo;
|
||||
|
||||
Write path: same as in :ref:`seqcount_t`, while running from a context
|
||||
with the associated LOCKTYPE lock acquired.
|
||||
with the associated write serialization lock acquired.
|
||||
|
||||
Read path: same as in :ref:`seqcount_t`.
|
||||
|
||||
|
|
|
|||
|
|
@ -2982,6 +2982,8 @@ L: linux-kernel@vger.kernel.org
|
|||
S: Maintained
|
||||
F: arch/*/include/asm/atomic*.h
|
||||
F: include/*/atomic*.h
|
||||
F: include/linux/refcount.h
|
||||
F: Documentation/atomic_*.txt
|
||||
F: scripts/atomic/
|
||||
|
||||
ATTO EXPRESSSAS SAS/SATA RAID SCSI DRIVER
|
||||
|
|
|
|||
|
|
@ -28,8 +28,7 @@ struct completion {
|
|||
struct swait_queue_head wait;
|
||||
};
|
||||
|
||||
#define init_completion_map(x, m) __init_completion(x)
|
||||
#define init_completion(x) __init_completion(x)
|
||||
#define init_completion_map(x, m) init_completion(x)
|
||||
static inline void complete_acquire(struct completion *x) {}
|
||||
static inline void complete_release(struct completion *x) {}
|
||||
|
||||
|
|
@ -82,7 +81,7 @@ static inline void complete_release(struct completion *x) {}
|
|||
* This inline function will initialize a dynamically created completion
|
||||
* structure.
|
||||
*/
|
||||
static inline void __init_completion(struct completion *x)
|
||||
static inline void init_completion(struct completion *x)
|
||||
{
|
||||
x->done = 0;
|
||||
init_swait_queue_head(&x->wait);
|
||||
|
|
|
|||
|
|
@ -101,7 +101,7 @@
|
|||
struct mutex;
|
||||
|
||||
/**
|
||||
* struct refcount_t - variant of atomic_t specialized for reference counts
|
||||
* typedef refcount_t - variant of atomic_t specialized for reference counts
|
||||
* @refs: atomic_t counter field
|
||||
*
|
||||
* The counter saturates at REFCOUNT_SATURATED and will not move once
|
||||
|
|
|
|||
|
|
@ -123,6 +123,7 @@ static inline int rwsem_is_contended(struct rw_semaphore *sem)
|
|||
* lock for reading
|
||||
*/
|
||||
extern void down_read(struct rw_semaphore *sem);
|
||||
extern int __must_check down_read_interruptible(struct rw_semaphore *sem);
|
||||
extern int __must_check down_read_killable(struct rw_semaphore *sem);
|
||||
|
||||
/*
|
||||
|
|
@ -171,6 +172,7 @@ extern void downgrade_write(struct rw_semaphore *sem);
|
|||
* See Documentation/locking/lockdep-design.rst for more details.)
|
||||
*/
|
||||
extern void down_read_nested(struct rw_semaphore *sem, int subclass);
|
||||
extern int __must_check down_read_killable_nested(struct rw_semaphore *sem, int subclass);
|
||||
extern void down_write_nested(struct rw_semaphore *sem, int subclass);
|
||||
extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass);
|
||||
extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
|
||||
|
|
@ -191,6 +193,7 @@ extern void down_read_non_owner(struct rw_semaphore *sem);
|
|||
extern void up_read_non_owner(struct rw_semaphore *sem);
|
||||
#else
|
||||
# define down_read_nested(sem, subclass) down_read(sem)
|
||||
# define down_read_killable_nested(sem, subclass) down_read_killable(sem)
|
||||
# define down_write_nest_lock(sem, nest_lock) down_write(sem)
|
||||
# define down_write_nested(sem, subclass) down_write(sem)
|
||||
# define down_write_killable_nested(sem, subclass) down_write_killable(sem)
|
||||
|
|
|
|||
|
|
@ -307,10 +307,10 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu
|
|||
__seqprop_case((s), mutex, prop), \
|
||||
__seqprop_case((s), ww_mutex, prop))
|
||||
|
||||
#define __seqcount_ptr(s) __seqprop(s, ptr)
|
||||
#define __seqcount_sequence(s) __seqprop(s, sequence)
|
||||
#define __seqcount_lock_preemptible(s) __seqprop(s, preemptible)
|
||||
#define __seqcount_assert_lock_held(s) __seqprop(s, assert)
|
||||
#define seqprop_ptr(s) __seqprop(s, ptr)
|
||||
#define seqprop_sequence(s) __seqprop(s, sequence)
|
||||
#define seqprop_preemptible(s) __seqprop(s, preemptible)
|
||||
#define seqprop_assert(s) __seqprop(s, assert)
|
||||
|
||||
/**
|
||||
* __read_seqcount_begin() - begin a seqcount_t read section w/o barrier
|
||||
|
|
@ -328,13 +328,13 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu
|
|||
*/
|
||||
#define __read_seqcount_begin(s) \
|
||||
({ \
|
||||
unsigned seq; \
|
||||
unsigned __seq; \
|
||||
\
|
||||
while ((seq = __seqcount_sequence(s)) & 1) \
|
||||
while ((__seq = seqprop_sequence(s)) & 1) \
|
||||
cpu_relax(); \
|
||||
\
|
||||
kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX); \
|
||||
seq; \
|
||||
__seq; \
|
||||
})
|
||||
|
||||
/**
|
||||
|
|
@ -345,10 +345,10 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu
|
|||
*/
|
||||
#define raw_read_seqcount_begin(s) \
|
||||
({ \
|
||||
unsigned seq = __read_seqcount_begin(s); \
|
||||
unsigned _seq = __read_seqcount_begin(s); \
|
||||
\
|
||||
smp_rmb(); \
|
||||
seq; \
|
||||
_seq; \
|
||||
})
|
||||
|
||||
/**
|
||||
|
|
@ -359,7 +359,7 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu
|
|||
*/
|
||||
#define read_seqcount_begin(s) \
|
||||
({ \
|
||||
seqcount_lockdep_reader_access(__seqcount_ptr(s)); \
|
||||
seqcount_lockdep_reader_access(seqprop_ptr(s)); \
|
||||
raw_read_seqcount_begin(s); \
|
||||
})
|
||||
|
||||
|
|
@ -376,11 +376,11 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu
|
|||
*/
|
||||
#define raw_read_seqcount(s) \
|
||||
({ \
|
||||
unsigned seq = __seqcount_sequence(s); \
|
||||
unsigned __seq = seqprop_sequence(s); \
|
||||
\
|
||||
smp_rmb(); \
|
||||
kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX); \
|
||||
seq; \
|
||||
__seq; \
|
||||
})
|
||||
|
||||
/**
|
||||
|
|
@ -425,9 +425,9 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu
|
|||
* Return: true if a read section retry is required, else false
|
||||
*/
|
||||
#define __read_seqcount_retry(s, start) \
|
||||
__read_seqcount_t_retry(__seqcount_ptr(s), start)
|
||||
do___read_seqcount_retry(seqprop_ptr(s), start)
|
||||
|
||||
static inline int __read_seqcount_t_retry(const seqcount_t *s, unsigned start)
|
||||
static inline int do___read_seqcount_retry(const seqcount_t *s, unsigned start)
|
||||
{
|
||||
kcsan_atomic_next(0);
|
||||
return unlikely(READ_ONCE(s->sequence) != start);
|
||||
|
|
@ -445,27 +445,29 @@ static inline int __read_seqcount_t_retry(const seqcount_t *s, unsigned start)
|
|||
* Return: true if a read section retry is required, else false
|
||||
*/
|
||||
#define read_seqcount_retry(s, start) \
|
||||
read_seqcount_t_retry(__seqcount_ptr(s), start)
|
||||
do_read_seqcount_retry(seqprop_ptr(s), start)
|
||||
|
||||
static inline int read_seqcount_t_retry(const seqcount_t *s, unsigned start)
|
||||
static inline int do_read_seqcount_retry(const seqcount_t *s, unsigned start)
|
||||
{
|
||||
smp_rmb();
|
||||
return __read_seqcount_t_retry(s, start);
|
||||
return do___read_seqcount_retry(s, start);
|
||||
}
|
||||
|
||||
/**
|
||||
* raw_write_seqcount_begin() - start a seqcount_t write section w/o lockdep
|
||||
* @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
|
||||
*
|
||||
* Context: check write_seqcount_begin()
|
||||
*/
|
||||
#define raw_write_seqcount_begin(s) \
|
||||
do { \
|
||||
if (__seqcount_lock_preemptible(s)) \
|
||||
if (seqprop_preemptible(s)) \
|
||||
preempt_disable(); \
|
||||
\
|
||||
raw_write_seqcount_t_begin(__seqcount_ptr(s)); \
|
||||
do_raw_write_seqcount_begin(seqprop_ptr(s)); \
|
||||
} while (0)
|
||||
|
||||
static inline void raw_write_seqcount_t_begin(seqcount_t *s)
|
||||
static inline void do_raw_write_seqcount_begin(seqcount_t *s)
|
||||
{
|
||||
kcsan_nestable_atomic_begin();
|
||||
s->sequence++;
|
||||
|
|
@ -475,16 +477,18 @@ static inline void raw_write_seqcount_t_begin(seqcount_t *s)
|
|||
/**
|
||||
* raw_write_seqcount_end() - end a seqcount_t write section w/o lockdep
|
||||
* @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
|
||||
*
|
||||
* Context: check write_seqcount_end()
|
||||
*/
|
||||
#define raw_write_seqcount_end(s) \
|
||||
do { \
|
||||
raw_write_seqcount_t_end(__seqcount_ptr(s)); \
|
||||
do_raw_write_seqcount_end(seqprop_ptr(s)); \
|
||||
\
|
||||
if (__seqcount_lock_preemptible(s)) \
|
||||
if (seqprop_preemptible(s)) \
|
||||
preempt_enable(); \
|
||||
} while (0)
|
||||
|
||||
static inline void raw_write_seqcount_t_end(seqcount_t *s)
|
||||
static inline void do_raw_write_seqcount_end(seqcount_t *s)
|
||||
{
|
||||
smp_wmb();
|
||||
s->sequence++;
|
||||
|
|
@ -498,20 +502,21 @@ static inline void raw_write_seqcount_t_end(seqcount_t *s)
|
|||
* @subclass: lockdep nesting level
|
||||
*
|
||||
* See Documentation/locking/lockdep-design.rst
|
||||
* Context: check write_seqcount_begin()
|
||||
*/
|
||||
#define write_seqcount_begin_nested(s, subclass) \
|
||||
do { \
|
||||
__seqcount_assert_lock_held(s); \
|
||||
seqprop_assert(s); \
|
||||
\
|
||||
if (__seqcount_lock_preemptible(s)) \
|
||||
if (seqprop_preemptible(s)) \
|
||||
preempt_disable(); \
|
||||
\
|
||||
write_seqcount_t_begin_nested(__seqcount_ptr(s), subclass); \
|
||||
do_write_seqcount_begin_nested(seqprop_ptr(s), subclass); \
|
||||
} while (0)
|
||||
|
||||
static inline void write_seqcount_t_begin_nested(seqcount_t *s, int subclass)
|
||||
static inline void do_write_seqcount_begin_nested(seqcount_t *s, int subclass)
|
||||
{
|
||||
raw_write_seqcount_t_begin(s);
|
||||
do_raw_write_seqcount_begin(s);
|
||||
seqcount_acquire(&s->dep_map, subclass, 0, _RET_IP_);
|
||||
}
|
||||
|
||||
|
|
@ -519,46 +524,46 @@ static inline void write_seqcount_t_begin_nested(seqcount_t *s, int subclass)
|
|||
* write_seqcount_begin() - start a seqcount_t write side critical section
|
||||
* @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
|
||||
*
|
||||
* write_seqcount_begin opens a write side critical section of the given
|
||||
* seqcount_t.
|
||||
*
|
||||
* Context: seqcount_t write side critical sections must be serialized and
|
||||
* non-preemptible. If readers can be invoked from hardirq or softirq
|
||||
* Context: sequence counter write side sections must be serialized and
|
||||
* non-preemptible. Preemption will be automatically disabled if and
|
||||
* only if the seqcount write serialization lock is associated, and
|
||||
* preemptible. If readers can be invoked from hardirq or softirq
|
||||
* context, interrupts or bottom halves must be respectively disabled.
|
||||
*/
|
||||
#define write_seqcount_begin(s) \
|
||||
do { \
|
||||
__seqcount_assert_lock_held(s); \
|
||||
seqprop_assert(s); \
|
||||
\
|
||||
if (__seqcount_lock_preemptible(s)) \
|
||||
if (seqprop_preemptible(s)) \
|
||||
preempt_disable(); \
|
||||
\
|
||||
write_seqcount_t_begin(__seqcount_ptr(s)); \
|
||||
do_write_seqcount_begin(seqprop_ptr(s)); \
|
||||
} while (0)
|
||||
|
||||
static inline void write_seqcount_t_begin(seqcount_t *s)
|
||||
static inline void do_write_seqcount_begin(seqcount_t *s)
|
||||
{
|
||||
write_seqcount_t_begin_nested(s, 0);
|
||||
do_write_seqcount_begin_nested(s, 0);
|
||||
}
|
||||
|
||||
/**
|
||||
* write_seqcount_end() - end a seqcount_t write side critical section
|
||||
* @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
|
||||
*
|
||||
* The write section must've been opened with write_seqcount_begin().
|
||||
* Context: Preemption will be automatically re-enabled if and only if
|
||||
* the seqcount write serialization lock is associated, and preemptible.
|
||||
*/
|
||||
#define write_seqcount_end(s) \
|
||||
do { \
|
||||
write_seqcount_t_end(__seqcount_ptr(s)); \
|
||||
do_write_seqcount_end(seqprop_ptr(s)); \
|
||||
\
|
||||
if (__seqcount_lock_preemptible(s)) \
|
||||
if (seqprop_preemptible(s)) \
|
||||
preempt_enable(); \
|
||||
} while (0)
|
||||
|
||||
static inline void write_seqcount_t_end(seqcount_t *s)
|
||||
static inline void do_write_seqcount_end(seqcount_t *s)
|
||||
{
|
||||
seqcount_release(&s->dep_map, _RET_IP_);
|
||||
raw_write_seqcount_t_end(s);
|
||||
do_raw_write_seqcount_end(s);
|
||||
}
|
||||
|
||||
/**
|
||||
|
|
@ -603,9 +608,9 @@ static inline void write_seqcount_t_end(seqcount_t *s)
|
|||
* }
|
||||
*/
|
||||
#define raw_write_seqcount_barrier(s) \
|
||||
raw_write_seqcount_t_barrier(__seqcount_ptr(s))
|
||||
do_raw_write_seqcount_barrier(seqprop_ptr(s))
|
||||
|
||||
static inline void raw_write_seqcount_t_barrier(seqcount_t *s)
|
||||
static inline void do_raw_write_seqcount_barrier(seqcount_t *s)
|
||||
{
|
||||
kcsan_nestable_atomic_begin();
|
||||
s->sequence++;
|
||||
|
|
@ -623,9 +628,9 @@ static inline void raw_write_seqcount_t_barrier(seqcount_t *s)
|
|||
* will complete successfully and see data older than this.
|
||||
*/
|
||||
#define write_seqcount_invalidate(s) \
|
||||
write_seqcount_t_invalidate(__seqcount_ptr(s))
|
||||
do_write_seqcount_invalidate(seqprop_ptr(s))
|
||||
|
||||
static inline void write_seqcount_t_invalidate(seqcount_t *s)
|
||||
static inline void do_write_seqcount_invalidate(seqcount_t *s)
|
||||
{
|
||||
smp_wmb();
|
||||
kcsan_nestable_atomic_begin();
|
||||
|
|
@ -865,9 +870,9 @@ static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start)
|
|||
}
|
||||
|
||||
/*
|
||||
* For all seqlock_t write side functions, use write_seqcount_*t*_begin()
|
||||
* instead of the generic write_seqcount_begin(). This way, no redundant
|
||||
* lockdep_assert_held() checks are added.
|
||||
* For all seqlock_t write side functions, use the the internal
|
||||
* do_write_seqcount_begin() instead of generic write_seqcount_begin().
|
||||
* This way, no redundant lockdep_assert_held() checks are added.
|
||||
*/
|
||||
|
||||
/**
|
||||
|
|
@ -886,7 +891,7 @@ static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start)
|
|||
static inline void write_seqlock(seqlock_t *sl)
|
||||
{
|
||||
spin_lock(&sl->lock);
|
||||
write_seqcount_t_begin(&sl->seqcount.seqcount);
|
||||
do_write_seqcount_begin(&sl->seqcount.seqcount);
|
||||
}
|
||||
|
||||
/**
|
||||
|
|
@ -898,7 +903,7 @@ static inline void write_seqlock(seqlock_t *sl)
|
|||
*/
|
||||
static inline void write_sequnlock(seqlock_t *sl)
|
||||
{
|
||||
write_seqcount_t_end(&sl->seqcount.seqcount);
|
||||
do_write_seqcount_end(&sl->seqcount.seqcount);
|
||||
spin_unlock(&sl->lock);
|
||||
}
|
||||
|
||||
|
|
@ -912,7 +917,7 @@ static inline void write_sequnlock(seqlock_t *sl)
|
|||
static inline void write_seqlock_bh(seqlock_t *sl)
|
||||
{
|
||||
spin_lock_bh(&sl->lock);
|
||||
write_seqcount_t_begin(&sl->seqcount.seqcount);
|
||||
do_write_seqcount_begin(&sl->seqcount.seqcount);
|
||||
}
|
||||
|
||||
/**
|
||||
|
|
@ -925,7 +930,7 @@ static inline void write_seqlock_bh(seqlock_t *sl)
|
|||
*/
|
||||
static inline void write_sequnlock_bh(seqlock_t *sl)
|
||||
{
|
||||
write_seqcount_t_end(&sl->seqcount.seqcount);
|
||||
do_write_seqcount_end(&sl->seqcount.seqcount);
|
||||
spin_unlock_bh(&sl->lock);
|
||||
}
|
||||
|
||||
|
|
@ -939,7 +944,7 @@ static inline void write_sequnlock_bh(seqlock_t *sl)
|
|||
static inline void write_seqlock_irq(seqlock_t *sl)
|
||||
{
|
||||
spin_lock_irq(&sl->lock);
|
||||
write_seqcount_t_begin(&sl->seqcount.seqcount);
|
||||
do_write_seqcount_begin(&sl->seqcount.seqcount);
|
||||
}
|
||||
|
||||
/**
|
||||
|
|
@ -951,7 +956,7 @@ static inline void write_seqlock_irq(seqlock_t *sl)
|
|||
*/
|
||||
static inline void write_sequnlock_irq(seqlock_t *sl)
|
||||
{
|
||||
write_seqcount_t_end(&sl->seqcount.seqcount);
|
||||
do_write_seqcount_end(&sl->seqcount.seqcount);
|
||||
spin_unlock_irq(&sl->lock);
|
||||
}
|
||||
|
||||
|
|
@ -960,7 +965,7 @@ static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl)
|
|||
unsigned long flags;
|
||||
|
||||
spin_lock_irqsave(&sl->lock, flags);
|
||||
write_seqcount_t_begin(&sl->seqcount.seqcount);
|
||||
do_write_seqcount_begin(&sl->seqcount.seqcount);
|
||||
return flags;
|
||||
}
|
||||
|
||||
|
|
@ -989,7 +994,7 @@ static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl)
|
|||
static inline void
|
||||
write_sequnlock_irqrestore(seqlock_t *sl, unsigned long flags)
|
||||
{
|
||||
write_seqcount_t_end(&sl->seqcount.seqcount);
|
||||
do_write_seqcount_end(&sl->seqcount.seqcount);
|
||||
spin_unlock_irqrestore(&sl->lock, flags);
|
||||
}
|
||||
|
||||
|
|
|
|||
|
|
@ -310,8 +310,6 @@ static inline bool should_fail_futex(bool fshared)
|
|||
|
||||
#ifdef CONFIG_COMPAT
|
||||
static void compat_exit_robust_list(struct task_struct *curr);
|
||||
#else
|
||||
static inline void compat_exit_robust_list(struct task_struct *curr) { }
|
||||
#endif
|
||||
|
||||
/*
|
||||
|
|
|
|||
|
|
@ -56,13 +56,11 @@ LOCK_EVENT(rwsem_sleep_reader) /* # of reader sleeps */
|
|||
LOCK_EVENT(rwsem_sleep_writer) /* # of writer sleeps */
|
||||
LOCK_EVENT(rwsem_wake_reader) /* # of reader wakeups */
|
||||
LOCK_EVENT(rwsem_wake_writer) /* # of writer wakeups */
|
||||
LOCK_EVENT(rwsem_opt_rlock) /* # of opt-acquired read locks */
|
||||
LOCK_EVENT(rwsem_opt_wlock) /* # of opt-acquired write locks */
|
||||
LOCK_EVENT(rwsem_opt_lock) /* # of opt-acquired write locks */
|
||||
LOCK_EVENT(rwsem_opt_fail) /* # of failed optspins */
|
||||
LOCK_EVENT(rwsem_opt_nospin) /* # of disabled optspins */
|
||||
LOCK_EVENT(rwsem_opt_norspin) /* # of disabled reader-only optspins */
|
||||
LOCK_EVENT(rwsem_opt_rlock2) /* # of opt-acquired 2ndary read locks */
|
||||
LOCK_EVENT(rwsem_rlock) /* # of read locks acquired */
|
||||
LOCK_EVENT(rwsem_rlock_steal) /* # of read locks by lock stealing */
|
||||
LOCK_EVENT(rwsem_rlock_fast) /* # of fast read locks acquired */
|
||||
LOCK_EVENT(rwsem_rlock_fail) /* # of failed read lock acquisitions */
|
||||
LOCK_EVENT(rwsem_rlock_handoff) /* # of read lock handoffs */
|
||||
|
|
|
|||
|
|
@ -31,19 +31,13 @@
|
|||
#include "lock_events.h"
|
||||
|
||||
/*
|
||||
* The least significant 3 bits of the owner value has the following
|
||||
* The least significant 2 bits of the owner value has the following
|
||||
* meanings when set.
|
||||
* - Bit 0: RWSEM_READER_OWNED - The rwsem is owned by readers
|
||||
* - Bit 1: RWSEM_RD_NONSPINNABLE - Readers cannot spin on this lock.
|
||||
* - Bit 2: RWSEM_WR_NONSPINNABLE - Writers cannot spin on this lock.
|
||||
* - Bit 1: RWSEM_NONSPINNABLE - Cannot spin on a reader-owned lock
|
||||
*
|
||||
* When the rwsem is either owned by an anonymous writer, or it is
|
||||
* reader-owned, but a spinning writer has timed out, both nonspinnable
|
||||
* bits will be set to disable optimistic spinning by readers and writers.
|
||||
* In the later case, the last unlocking reader should then check the
|
||||
* writer nonspinnable bit and clear it only to give writers preference
|
||||
* to acquire the lock via optimistic spinning, but not readers. Similar
|
||||
* action is also done in the reader slowpath.
|
||||
* When the rwsem is reader-owned and a spinning writer has timed out,
|
||||
* the nonspinnable bit will be set to disable optimistic spinning.
|
||||
|
||||
* When a writer acquires a rwsem, it puts its task_struct pointer
|
||||
* into the owner field. It is cleared after an unlock.
|
||||
|
|
@ -59,46 +53,14 @@
|
|||
* is involved. Ideally we would like to track all the readers that own
|
||||
* a rwsem, but the overhead is simply too big.
|
||||
*
|
||||
* Reader optimistic spinning is helpful when the reader critical section
|
||||
* is short and there aren't that many readers around. It makes readers
|
||||
* relatively more preferred than writers. When a writer times out spinning
|
||||
* on a reader-owned lock and set the nospinnable bits, there are two main
|
||||
* reasons for that.
|
||||
*
|
||||
* 1) The reader critical section is long, perhaps the task sleeps after
|
||||
* acquiring the read lock.
|
||||
* 2) There are just too many readers contending the lock causing it to
|
||||
* take a while to service all of them.
|
||||
*
|
||||
* In the former case, long reader critical section will impede the progress
|
||||
* of writers which is usually more important for system performance. In
|
||||
* the later case, reader optimistic spinning tends to make the reader
|
||||
* groups that contain readers that acquire the lock together smaller
|
||||
* leading to more of them. That may hurt performance in some cases. In
|
||||
* other words, the setting of nonspinnable bits indicates that reader
|
||||
* optimistic spinning may not be helpful for those workloads that cause
|
||||
* it.
|
||||
*
|
||||
* Therefore, any writers that had observed the setting of the writer
|
||||
* nonspinnable bit for a given rwsem after they fail to acquire the lock
|
||||
* via optimistic spinning will set the reader nonspinnable bit once they
|
||||
* acquire the write lock. Similarly, readers that observe the setting
|
||||
* of reader nonspinnable bit at slowpath entry will set the reader
|
||||
* nonspinnable bits when they acquire the read lock via the wakeup path.
|
||||
*
|
||||
* Once the reader nonspinnable bit is on, it will only be reset when
|
||||
* a writer is able to acquire the rwsem in the fast path or somehow a
|
||||
* reader or writer in the slowpath doesn't observe the nonspinable bit.
|
||||
*
|
||||
* This is to discourage reader optmistic spinning on that particular
|
||||
* rwsem and make writers more preferred. This adaptive disabling of reader
|
||||
* optimistic spinning will alleviate the negative side effect of this
|
||||
* feature.
|
||||
* A fast path reader optimistic lock stealing is supported when the rwsem
|
||||
* is previously owned by a writer and the following conditions are met:
|
||||
* - OSQ is empty
|
||||
* - rwsem is not currently writer owned
|
||||
* - the handoff isn't set.
|
||||
*/
|
||||
#define RWSEM_READER_OWNED (1UL << 0)
|
||||
#define RWSEM_RD_NONSPINNABLE (1UL << 1)
|
||||
#define RWSEM_WR_NONSPINNABLE (1UL << 2)
|
||||
#define RWSEM_NONSPINNABLE (RWSEM_RD_NONSPINNABLE | RWSEM_WR_NONSPINNABLE)
|
||||
#define RWSEM_NONSPINNABLE (1UL << 1)
|
||||
#define RWSEM_OWNER_FLAGS_MASK (RWSEM_READER_OWNED | RWSEM_NONSPINNABLE)
|
||||
|
||||
#ifdef CONFIG_DEBUG_RWSEMS
|
||||
|
|
@ -203,7 +165,7 @@ static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
|
|||
struct task_struct *owner)
|
||||
{
|
||||
unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED |
|
||||
(atomic_long_read(&sem->owner) & RWSEM_RD_NONSPINNABLE);
|
||||
(atomic_long_read(&sem->owner) & RWSEM_NONSPINNABLE);
|
||||
|
||||
atomic_long_set(&sem->owner, val);
|
||||
}
|
||||
|
|
@ -270,12 +232,31 @@ static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
|
|||
owner | RWSEM_NONSPINNABLE));
|
||||
}
|
||||
|
||||
static inline bool rwsem_read_trylock(struct rw_semaphore *sem)
|
||||
static inline bool rwsem_read_trylock(struct rw_semaphore *sem, long *cntp)
|
||||
{
|
||||
long cnt = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
|
||||
if (WARN_ON_ONCE(cnt < 0))
|
||||
*cntp = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
|
||||
|
||||
if (WARN_ON_ONCE(*cntp < 0))
|
||||
rwsem_set_nonspinnable(sem);
|
||||
return !(cnt & RWSEM_READ_FAILED_MASK);
|
||||
|
||||
if (!(*cntp & RWSEM_READ_FAILED_MASK)) {
|
||||
rwsem_set_reader_owned(sem);
|
||||
return true;
|
||||
}
|
||||
|
||||
return false;
|
||||
}
|
||||
|
||||
static inline bool rwsem_write_trylock(struct rw_semaphore *sem)
|
||||
{
|
||||
long tmp = RWSEM_UNLOCKED_VALUE;
|
||||
|
||||
if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp, RWSEM_WRITER_LOCKED)) {
|
||||
rwsem_set_owner(sem);
|
||||
return true;
|
||||
}
|
||||
|
||||
return false;
|
||||
}
|
||||
|
||||
/*
|
||||
|
|
@ -353,7 +334,6 @@ struct rwsem_waiter {
|
|||
struct task_struct *task;
|
||||
enum rwsem_waiter_type type;
|
||||
unsigned long timeout;
|
||||
unsigned long last_rowner;
|
||||
};
|
||||
#define rwsem_first_waiter(sem) \
|
||||
list_first_entry(&sem->wait_list, struct rwsem_waiter, list)
|
||||
|
|
@ -467,10 +447,6 @@ static void rwsem_mark_wake(struct rw_semaphore *sem,
|
|||
* the reader is copied over.
|
||||
*/
|
||||
owner = waiter->task;
|
||||
if (waiter->last_rowner & RWSEM_RD_NONSPINNABLE) {
|
||||
owner = (void *)((unsigned long)owner | RWSEM_RD_NONSPINNABLE);
|
||||
lockevent_inc(rwsem_opt_norspin);
|
||||
}
|
||||
__rwsem_set_reader_owned(sem, owner);
|
||||
}
|
||||
|
||||
|
|
@ -601,30 +577,6 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
|
|||
}
|
||||
|
||||
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
|
||||
/*
|
||||
* Try to acquire read lock before the reader is put on wait queue.
|
||||
* Lock acquisition isn't allowed if the rwsem is locked or a writer handoff
|
||||
* is ongoing.
|
||||
*/
|
||||
static inline bool rwsem_try_read_lock_unqueued(struct rw_semaphore *sem)
|
||||
{
|
||||
long count = atomic_long_read(&sem->count);
|
||||
|
||||
if (count & (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))
|
||||
return false;
|
||||
|
||||
count = atomic_long_fetch_add_acquire(RWSEM_READER_BIAS, &sem->count);
|
||||
if (!(count & (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
|
||||
rwsem_set_reader_owned(sem);
|
||||
lockevent_inc(rwsem_opt_rlock);
|
||||
return true;
|
||||
}
|
||||
|
||||
/* Back out the change */
|
||||
atomic_long_add(-RWSEM_READER_BIAS, &sem->count);
|
||||
return false;
|
||||
}
|
||||
|
||||
/*
|
||||
* Try to acquire write lock before the writer has been put on wait queue.
|
||||
*/
|
||||
|
|
@ -636,7 +588,7 @@ static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
|
|||
if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,
|
||||
count | RWSEM_WRITER_LOCKED)) {
|
||||
rwsem_set_owner(sem);
|
||||
lockevent_inc(rwsem_opt_wlock);
|
||||
lockevent_inc(rwsem_opt_lock);
|
||||
return true;
|
||||
}
|
||||
}
|
||||
|
|
@ -652,8 +604,7 @@ static inline bool owner_on_cpu(struct task_struct *owner)
|
|||
return owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
|
||||
}
|
||||
|
||||
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem,
|
||||
unsigned long nonspinnable)
|
||||
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
|
||||
{
|
||||
struct task_struct *owner;
|
||||
unsigned long flags;
|
||||
|
|
@ -670,7 +621,7 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem,
|
|||
/*
|
||||
* Don't check the read-owner as the entry may be stale.
|
||||
*/
|
||||
if ((flags & nonspinnable) ||
|
||||
if ((flags & RWSEM_NONSPINNABLE) ||
|
||||
(owner && !(flags & RWSEM_READER_OWNED) && !owner_on_cpu(owner)))
|
||||
ret = false;
|
||||
rcu_read_unlock();
|
||||
|
|
@ -700,9 +651,9 @@ enum owner_state {
|
|||
#define OWNER_SPINNABLE (OWNER_NULL | OWNER_WRITER | OWNER_READER)
|
||||
|
||||
static inline enum owner_state
|
||||
rwsem_owner_state(struct task_struct *owner, unsigned long flags, unsigned long nonspinnable)
|
||||
rwsem_owner_state(struct task_struct *owner, unsigned long flags)
|
||||
{
|
||||
if (flags & nonspinnable)
|
||||
if (flags & RWSEM_NONSPINNABLE)
|
||||
return OWNER_NONSPINNABLE;
|
||||
|
||||
if (flags & RWSEM_READER_OWNED)
|
||||
|
|
@ -712,14 +663,14 @@ rwsem_owner_state(struct task_struct *owner, unsigned long flags, unsigned long
|
|||
}
|
||||
|
||||
static noinline enum owner_state
|
||||
rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
|
||||
rwsem_spin_on_owner(struct rw_semaphore *sem)
|
||||
{
|
||||
struct task_struct *new, *owner;
|
||||
unsigned long flags, new_flags;
|
||||
enum owner_state state;
|
||||
|
||||
owner = rwsem_owner_flags(sem, &flags);
|
||||
state = rwsem_owner_state(owner, flags, nonspinnable);
|
||||
state = rwsem_owner_state(owner, flags);
|
||||
if (state != OWNER_WRITER)
|
||||
return state;
|
||||
|
||||
|
|
@ -733,7 +684,7 @@ rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
|
|||
*/
|
||||
new = rwsem_owner_flags(sem, &new_flags);
|
||||
if ((new != owner) || (new_flags != flags)) {
|
||||
state = rwsem_owner_state(new, new_flags, nonspinnable);
|
||||
state = rwsem_owner_state(new, new_flags);
|
||||
break;
|
||||
}
|
||||
|
||||
|
|
@ -782,14 +733,12 @@ static inline u64 rwsem_rspin_threshold(struct rw_semaphore *sem)
|
|||
return sched_clock() + delta;
|
||||
}
|
||||
|
||||
static bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
|
||||
static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
|
||||
{
|
||||
bool taken = false;
|
||||
int prev_owner_state = OWNER_NULL;
|
||||
int loop = 0;
|
||||
u64 rspin_threshold = 0;
|
||||
unsigned long nonspinnable = wlock ? RWSEM_WR_NONSPINNABLE
|
||||
: RWSEM_RD_NONSPINNABLE;
|
||||
|
||||
preempt_disable();
|
||||
|
||||
|
|
@ -806,15 +755,14 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
|
|||
for (;;) {
|
||||
enum owner_state owner_state;
|
||||
|
||||
owner_state = rwsem_spin_on_owner(sem, nonspinnable);
|
||||
owner_state = rwsem_spin_on_owner(sem);
|
||||
if (!(owner_state & OWNER_SPINNABLE))
|
||||
break;
|
||||
|
||||
/*
|
||||
* Try to acquire the lock
|
||||
*/
|
||||
taken = wlock ? rwsem_try_write_lock_unqueued(sem)
|
||||
: rwsem_try_read_lock_unqueued(sem);
|
||||
taken = rwsem_try_write_lock_unqueued(sem);
|
||||
|
||||
if (taken)
|
||||
break;
|
||||
|
|
@ -822,7 +770,7 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
|
|||
/*
|
||||
* Time-based reader-owned rwsem optimistic spinning
|
||||
*/
|
||||
if (wlock && (owner_state == OWNER_READER)) {
|
||||
if (owner_state == OWNER_READER) {
|
||||
/*
|
||||
* Re-initialize rspin_threshold every time when
|
||||
* the owner state changes from non-reader to reader.
|
||||
|
|
@ -831,7 +779,7 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
|
|||
* the beginning of the 2nd reader phase.
|
||||
*/
|
||||
if (prev_owner_state != OWNER_READER) {
|
||||
if (rwsem_test_oflags(sem, nonspinnable))
|
||||
if (rwsem_test_oflags(sem, RWSEM_NONSPINNABLE))
|
||||
break;
|
||||
rspin_threshold = rwsem_rspin_threshold(sem);
|
||||
loop = 0;
|
||||
|
|
@ -907,78 +855,30 @@ done:
|
|||
}
|
||||
|
||||
/*
|
||||
* Clear the owner's RWSEM_WR_NONSPINNABLE bit if it is set. This should
|
||||
* Clear the owner's RWSEM_NONSPINNABLE bit if it is set. This should
|
||||
* only be called when the reader count reaches 0.
|
||||
*
|
||||
* This give writers better chance to acquire the rwsem first before
|
||||
* readers when the rwsem was being held by readers for a relatively long
|
||||
* period of time. Race can happen that an optimistic spinner may have
|
||||
* just stolen the rwsem and set the owner, but just clearing the
|
||||
* RWSEM_WR_NONSPINNABLE bit will do no harm anyway.
|
||||
*/
|
||||
static inline void clear_wr_nonspinnable(struct rw_semaphore *sem)
|
||||
static inline void clear_nonspinnable(struct rw_semaphore *sem)
|
||||
{
|
||||
if (rwsem_test_oflags(sem, RWSEM_WR_NONSPINNABLE))
|
||||
atomic_long_andnot(RWSEM_WR_NONSPINNABLE, &sem->owner);
|
||||
if (rwsem_test_oflags(sem, RWSEM_NONSPINNABLE))
|
||||
atomic_long_andnot(RWSEM_NONSPINNABLE, &sem->owner);
|
||||
}
|
||||
|
||||
/*
|
||||
* This function is called when the reader fails to acquire the lock via
|
||||
* optimistic spinning. In this case we will still attempt to do a trylock
|
||||
* when comparing the rwsem state right now with the state when entering
|
||||
* the slowpath indicates that the reader is still in a valid reader phase.
|
||||
* This happens when the following conditions are true:
|
||||
*
|
||||
* 1) The lock is currently reader owned, and
|
||||
* 2) The lock is previously not reader-owned or the last read owner changes.
|
||||
*
|
||||
* In the former case, we have transitioned from a writer phase to a
|
||||
* reader-phase while spinning. In the latter case, it means the reader
|
||||
* phase hasn't ended when we entered the optimistic spinning loop. In
|
||||
* both cases, the reader is eligible to acquire the lock. This is the
|
||||
* secondary path where a read lock is acquired optimistically.
|
||||
*
|
||||
* The reader non-spinnable bit wasn't set at time of entry or it will
|
||||
* not be here at all.
|
||||
*/
|
||||
static inline bool rwsem_reader_phase_trylock(struct rw_semaphore *sem,
|
||||
unsigned long last_rowner)
|
||||
{
|
||||
unsigned long owner = atomic_long_read(&sem->owner);
|
||||
|
||||
if (!(owner & RWSEM_READER_OWNED))
|
||||
return false;
|
||||
|
||||
if (((owner ^ last_rowner) & ~RWSEM_OWNER_FLAGS_MASK) &&
|
||||
rwsem_try_read_lock_unqueued(sem)) {
|
||||
lockevent_inc(rwsem_opt_rlock2);
|
||||
lockevent_add(rwsem_opt_fail, -1);
|
||||
return true;
|
||||
}
|
||||
return false;
|
||||
}
|
||||
#else
|
||||
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem,
|
||||
unsigned long nonspinnable)
|
||||
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
|
||||
{
|
||||
return false;
|
||||
}
|
||||
|
||||
static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
|
||||
static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem)
|
||||
{
|
||||
return false;
|
||||
}
|
||||
|
||||
static inline void clear_wr_nonspinnable(struct rw_semaphore *sem) { }
|
||||
|
||||
static inline bool rwsem_reader_phase_trylock(struct rw_semaphore *sem,
|
||||
unsigned long last_rowner)
|
||||
{
|
||||
return false;
|
||||
}
|
||||
static inline void clear_nonspinnable(struct rw_semaphore *sem) { }
|
||||
|
||||
static inline int
|
||||
rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
|
||||
rwsem_spin_on_owner(struct rw_semaphore *sem)
|
||||
{
|
||||
return 0;
|
||||
}
|
||||
|
|
@ -989,36 +889,35 @@ rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
|
|||
* Wait for the read lock to be granted
|
||||
*/
|
||||
static struct rw_semaphore __sched *
|
||||
rwsem_down_read_slowpath(struct rw_semaphore *sem, int state)
|
||||
rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, int state)
|
||||
{
|
||||
long count, adjustment = -RWSEM_READER_BIAS;
|
||||
long adjustment = -RWSEM_READER_BIAS;
|
||||
long rcnt = (count >> RWSEM_READER_SHIFT);
|
||||
struct rwsem_waiter waiter;
|
||||
DEFINE_WAKE_Q(wake_q);
|
||||
bool wake = false;
|
||||
|
||||
/*
|
||||
* Save the current read-owner of rwsem, if available, and the
|
||||
* reader nonspinnable bit.
|
||||
* To prevent a constant stream of readers from starving a sleeping
|
||||
* waiter, don't attempt optimistic lock stealing if the lock is
|
||||
* currently owned by readers.
|
||||
*/
|
||||
waiter.last_rowner = atomic_long_read(&sem->owner);
|
||||
if (!(waiter.last_rowner & RWSEM_READER_OWNED))
|
||||
waiter.last_rowner &= RWSEM_RD_NONSPINNABLE;
|
||||
|
||||
if (!rwsem_can_spin_on_owner(sem, RWSEM_RD_NONSPINNABLE))
|
||||
if ((atomic_long_read(&sem->owner) & RWSEM_READER_OWNED) &&
|
||||
(rcnt > 1) && !(count & RWSEM_WRITER_LOCKED))
|
||||
goto queue;
|
||||
|
||||
/*
|
||||
* Undo read bias from down_read() and do optimistic spinning.
|
||||
* Reader optimistic lock stealing.
|
||||
*/
|
||||
atomic_long_add(-RWSEM_READER_BIAS, &sem->count);
|
||||
adjustment = 0;
|
||||
if (rwsem_optimistic_spin(sem, false)) {
|
||||
/* rwsem_optimistic_spin() implies ACQUIRE on success */
|
||||
if (!(count & (RWSEM_WRITER_LOCKED | RWSEM_FLAG_HANDOFF))) {
|
||||
rwsem_set_reader_owned(sem);
|
||||
lockevent_inc(rwsem_rlock_steal);
|
||||
|
||||
/*
|
||||
* Wake up other readers in the wait list if the front
|
||||
* waiter is a reader.
|
||||
* Wake up other readers in the wait queue if it is
|
||||
* the first reader.
|
||||
*/
|
||||
if ((atomic_long_read(&sem->count) & RWSEM_FLAG_WAITERS)) {
|
||||
if ((rcnt == 1) && (count & RWSEM_FLAG_WAITERS)) {
|
||||
raw_spin_lock_irq(&sem->wait_lock);
|
||||
if (!list_empty(&sem->wait_list))
|
||||
rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED,
|
||||
|
|
@ -1027,9 +926,6 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, int state)
|
|||
wake_up_q(&wake_q);
|
||||
}
|
||||
return sem;
|
||||
} else if (rwsem_reader_phase_trylock(sem, waiter.last_rowner)) {
|
||||
/* rwsem_reader_phase_trylock() implies ACQUIRE on success */
|
||||
return sem;
|
||||
}
|
||||
|
||||
queue:
|
||||
|
|
@ -1045,7 +941,7 @@ queue:
|
|||
* exit the slowpath and return immediately as its
|
||||
* RWSEM_READER_BIAS has already been set in the count.
|
||||
*/
|
||||
if (adjustment && !(atomic_long_read(&sem->count) &
|
||||
if (!(atomic_long_read(&sem->count) &
|
||||
(RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
|
||||
/* Provide lock ACQUIRE */
|
||||
smp_acquire__after_ctrl_dep();
|
||||
|
|
@ -1059,10 +955,7 @@ queue:
|
|||
list_add_tail(&waiter.list, &sem->wait_list);
|
||||
|
||||
/* we're now waiting on the lock, but no longer actively locking */
|
||||
if (adjustment)
|
||||
count = atomic_long_add_return(adjustment, &sem->count);
|
||||
else
|
||||
count = atomic_long_read(&sem->count);
|
||||
count = atomic_long_add_return(adjustment, &sem->count);
|
||||
|
||||
/*
|
||||
* If there are no active locks, wake the front queued process(es).
|
||||
|
|
@ -1071,7 +964,7 @@ queue:
|
|||
* wake our own waiter to join the existing active readers !
|
||||
*/
|
||||
if (!(count & RWSEM_LOCK_MASK)) {
|
||||
clear_wr_nonspinnable(sem);
|
||||
clear_nonspinnable(sem);
|
||||
wake = true;
|
||||
}
|
||||
if (wake || (!(count & RWSEM_WRITER_MASK) &&
|
||||
|
|
@ -1116,19 +1009,6 @@ out_nolock:
|
|||
return ERR_PTR(-EINTR);
|
||||
}
|
||||
|
||||
/*
|
||||
* This function is called by the a write lock owner. So the owner value
|
||||
* won't get changed by others.
|
||||
*/
|
||||
static inline void rwsem_disable_reader_optspin(struct rw_semaphore *sem,
|
||||
bool disable)
|
||||
{
|
||||
if (unlikely(disable)) {
|
||||
atomic_long_or(RWSEM_RD_NONSPINNABLE, &sem->owner);
|
||||
lockevent_inc(rwsem_opt_norspin);
|
||||
}
|
||||
}
|
||||
|
||||
/*
|
||||
* Wait until we successfully acquire the write lock
|
||||
*/
|
||||
|
|
@ -1136,26 +1016,17 @@ static struct rw_semaphore *
|
|||
rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
|
||||
{
|
||||
long count;
|
||||
bool disable_rspin;
|
||||
enum writer_wait_state wstate;
|
||||
struct rwsem_waiter waiter;
|
||||
struct rw_semaphore *ret = sem;
|
||||
DEFINE_WAKE_Q(wake_q);
|
||||
|
||||
/* do optimistic spinning and steal lock if possible */
|
||||
if (rwsem_can_spin_on_owner(sem, RWSEM_WR_NONSPINNABLE) &&
|
||||
rwsem_optimistic_spin(sem, true)) {
|
||||
if (rwsem_can_spin_on_owner(sem) && rwsem_optimistic_spin(sem)) {
|
||||
/* rwsem_optimistic_spin() implies ACQUIRE on success */
|
||||
return sem;
|
||||
}
|
||||
|
||||
/*
|
||||
* Disable reader optimistic spinning for this rwsem after
|
||||
* acquiring the write lock when the setting of the nonspinnable
|
||||
* bits are observed.
|
||||
*/
|
||||
disable_rspin = atomic_long_read(&sem->owner) & RWSEM_NONSPINNABLE;
|
||||
|
||||
/*
|
||||
* Optimistic spinning failed, proceed to the slowpath
|
||||
* and block until we can acquire the sem.
|
||||
|
|
@ -1224,7 +1095,7 @@ wait:
|
|||
* without sleeping.
|
||||
*/
|
||||
if (wstate == WRITER_HANDOFF &&
|
||||
rwsem_spin_on_owner(sem, RWSEM_NONSPINNABLE) == OWNER_NULL)
|
||||
rwsem_spin_on_owner(sem) == OWNER_NULL)
|
||||
goto trylock_again;
|
||||
|
||||
/* Block until there are no active lockers. */
|
||||
|
|
@ -1266,7 +1137,6 @@ trylock_again:
|
|||
}
|
||||
__set_current_state(TASK_RUNNING);
|
||||
list_del(&waiter.list);
|
||||
rwsem_disable_reader_optspin(sem, disable_rspin);
|
||||
raw_spin_unlock_irq(&sem->wait_lock);
|
||||
lockevent_inc(rwsem_wlock);
|
||||
|
||||
|
|
@ -1335,26 +1205,31 @@ static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
|
|||
/*
|
||||
* lock for reading
|
||||
*/
|
||||
static inline int __down_read_common(struct rw_semaphore *sem, int state)
|
||||
{
|
||||
long count;
|
||||
|
||||
if (!rwsem_read_trylock(sem, &count)) {
|
||||
if (IS_ERR(rwsem_down_read_slowpath(sem, count, state)))
|
||||
return -EINTR;
|
||||
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
|
||||
}
|
||||
return 0;
|
||||
}
|
||||
|
||||
static inline void __down_read(struct rw_semaphore *sem)
|
||||
{
|
||||
if (!rwsem_read_trylock(sem)) {
|
||||
rwsem_down_read_slowpath(sem, TASK_UNINTERRUPTIBLE);
|
||||
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
|
||||
} else {
|
||||
rwsem_set_reader_owned(sem);
|
||||
}
|
||||
__down_read_common(sem, TASK_UNINTERRUPTIBLE);
|
||||
}
|
||||
|
||||
static inline int __down_read_interruptible(struct rw_semaphore *sem)
|
||||
{
|
||||
return __down_read_common(sem, TASK_INTERRUPTIBLE);
|
||||
}
|
||||
|
||||
static inline int __down_read_killable(struct rw_semaphore *sem)
|
||||
{
|
||||
if (!rwsem_read_trylock(sem)) {
|
||||
if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_KILLABLE)))
|
||||
return -EINTR;
|
||||
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
|
||||
} else {
|
||||
rwsem_set_reader_owned(sem);
|
||||
}
|
||||
return 0;
|
||||
return __down_read_common(sem, TASK_KILLABLE);
|
||||
}
|
||||
|
||||
static inline int __down_read_trylock(struct rw_semaphore *sem)
|
||||
|
|
@ -1380,44 +1255,30 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
|
|||
/*
|
||||
* lock for writing
|
||||
*/
|
||||
static inline int __down_write_common(struct rw_semaphore *sem, int state)
|
||||
{
|
||||
if (unlikely(!rwsem_write_trylock(sem))) {
|
||||
if (IS_ERR(rwsem_down_write_slowpath(sem, state)))
|
||||
return -EINTR;
|
||||
}
|
||||
|
||||
return 0;
|
||||
}
|
||||
|
||||
static inline void __down_write(struct rw_semaphore *sem)
|
||||
{
|
||||
long tmp = RWSEM_UNLOCKED_VALUE;
|
||||
|
||||
if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
|
||||
RWSEM_WRITER_LOCKED)))
|
||||
rwsem_down_write_slowpath(sem, TASK_UNINTERRUPTIBLE);
|
||||
else
|
||||
rwsem_set_owner(sem);
|
||||
__down_write_common(sem, TASK_UNINTERRUPTIBLE);
|
||||
}
|
||||
|
||||
static inline int __down_write_killable(struct rw_semaphore *sem)
|
||||
{
|
||||
long tmp = RWSEM_UNLOCKED_VALUE;
|
||||
|
||||
if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
|
||||
RWSEM_WRITER_LOCKED))) {
|
||||
if (IS_ERR(rwsem_down_write_slowpath(sem, TASK_KILLABLE)))
|
||||
return -EINTR;
|
||||
} else {
|
||||
rwsem_set_owner(sem);
|
||||
}
|
||||
return 0;
|
||||
return __down_write_common(sem, TASK_KILLABLE);
|
||||
}
|
||||
|
||||
static inline int __down_write_trylock(struct rw_semaphore *sem)
|
||||
{
|
||||
long tmp;
|
||||
|
||||
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
|
||||
|
||||
tmp = RWSEM_UNLOCKED_VALUE;
|
||||
if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
|
||||
RWSEM_WRITER_LOCKED)) {
|
||||
rwsem_set_owner(sem);
|
||||
return true;
|
||||
}
|
||||
return false;
|
||||
return rwsem_write_trylock(sem);
|
||||
}
|
||||
|
||||
/*
|
||||
|
|
@ -1435,7 +1296,7 @@ static inline void __up_read(struct rw_semaphore *sem)
|
|||
DEBUG_RWSEMS_WARN_ON(tmp < 0, sem);
|
||||
if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) ==
|
||||
RWSEM_FLAG_WAITERS)) {
|
||||
clear_wr_nonspinnable(sem);
|
||||
clear_nonspinnable(sem);
|
||||
rwsem_wake(sem, tmp);
|
||||
}
|
||||
}
|
||||
|
|
@ -1495,6 +1356,20 @@ void __sched down_read(struct rw_semaphore *sem)
|
|||
}
|
||||
EXPORT_SYMBOL(down_read);
|
||||
|
||||
int __sched down_read_interruptible(struct rw_semaphore *sem)
|
||||
{
|
||||
might_sleep();
|
||||
rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
|
||||
|
||||
if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_interruptible)) {
|
||||
rwsem_release(&sem->dep_map, _RET_IP_);
|
||||
return -EINTR;
|
||||
}
|
||||
|
||||
return 0;
|
||||
}
|
||||
EXPORT_SYMBOL(down_read_interruptible);
|
||||
|
||||
int __sched down_read_killable(struct rw_semaphore *sem)
|
||||
{
|
||||
might_sleep();
|
||||
|
|
@ -1605,6 +1480,20 @@ void down_read_nested(struct rw_semaphore *sem, int subclass)
|
|||
}
|
||||
EXPORT_SYMBOL(down_read_nested);
|
||||
|
||||
int down_read_killable_nested(struct rw_semaphore *sem, int subclass)
|
||||
{
|
||||
might_sleep();
|
||||
rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
|
||||
|
||||
if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
|
||||
rwsem_release(&sem->dep_map, _RET_IP_);
|
||||
return -EINTR;
|
||||
}
|
||||
|
||||
return 0;
|
||||
}
|
||||
EXPORT_SYMBOL(down_read_killable_nested);
|
||||
|
||||
void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
|
||||
{
|
||||
might_sleep();
|
||||
|
|
|
|||
|
|
@ -58,10 +58,10 @@ static struct ww_mutex o, o2, o3;
|
|||
* Normal standalone locks, for the circular and irq-context
|
||||
* dependency tests:
|
||||
*/
|
||||
static DEFINE_RAW_SPINLOCK(lock_A);
|
||||
static DEFINE_RAW_SPINLOCK(lock_B);
|
||||
static DEFINE_RAW_SPINLOCK(lock_C);
|
||||
static DEFINE_RAW_SPINLOCK(lock_D);
|
||||
static DEFINE_SPINLOCK(lock_A);
|
||||
static DEFINE_SPINLOCK(lock_B);
|
||||
static DEFINE_SPINLOCK(lock_C);
|
||||
static DEFINE_SPINLOCK(lock_D);
|
||||
|
||||
static DEFINE_RWLOCK(rwlock_A);
|
||||
static DEFINE_RWLOCK(rwlock_B);
|
||||
|
|
@ -93,12 +93,12 @@ static DEFINE_RT_MUTEX(rtmutex_D);
|
|||
* but X* and Y* are different classes. We do this so that
|
||||
* we do not trigger a real lockup:
|
||||
*/
|
||||
static DEFINE_RAW_SPINLOCK(lock_X1);
|
||||
static DEFINE_RAW_SPINLOCK(lock_X2);
|
||||
static DEFINE_RAW_SPINLOCK(lock_Y1);
|
||||
static DEFINE_RAW_SPINLOCK(lock_Y2);
|
||||
static DEFINE_RAW_SPINLOCK(lock_Z1);
|
||||
static DEFINE_RAW_SPINLOCK(lock_Z2);
|
||||
static DEFINE_SPINLOCK(lock_X1);
|
||||
static DEFINE_SPINLOCK(lock_X2);
|
||||
static DEFINE_SPINLOCK(lock_Y1);
|
||||
static DEFINE_SPINLOCK(lock_Y2);
|
||||
static DEFINE_SPINLOCK(lock_Z1);
|
||||
static DEFINE_SPINLOCK(lock_Z2);
|
||||
|
||||
static DEFINE_RWLOCK(rwlock_X1);
|
||||
static DEFINE_RWLOCK(rwlock_X2);
|
||||
|
|
@ -138,10 +138,10 @@ static DEFINE_RT_MUTEX(rtmutex_Z2);
|
|||
*/
|
||||
#define INIT_CLASS_FUNC(class) \
|
||||
static noinline void \
|
||||
init_class_##class(raw_spinlock_t *lock, rwlock_t *rwlock, \
|
||||
init_class_##class(spinlock_t *lock, rwlock_t *rwlock, \
|
||||
struct mutex *mutex, struct rw_semaphore *rwsem)\
|
||||
{ \
|
||||
raw_spin_lock_init(lock); \
|
||||
spin_lock_init(lock); \
|
||||
rwlock_init(rwlock); \
|
||||
mutex_init(mutex); \
|
||||
init_rwsem(rwsem); \
|
||||
|
|
@ -210,10 +210,10 @@ static void init_shared_classes(void)
|
|||
* Shortcuts for lock/unlock API variants, to keep
|
||||
* the testcases compact:
|
||||
*/
|
||||
#define L(x) raw_spin_lock(&lock_##x)
|
||||
#define U(x) raw_spin_unlock(&lock_##x)
|
||||
#define L(x) spin_lock(&lock_##x)
|
||||
#define U(x) spin_unlock(&lock_##x)
|
||||
#define LU(x) L(x); U(x)
|
||||
#define SI(x) raw_spin_lock_init(&lock_##x)
|
||||
#define SI(x) spin_lock_init(&lock_##x)
|
||||
|
||||
#define WL(x) write_lock(&rwlock_##x)
|
||||
#define WU(x) write_unlock(&rwlock_##x)
|
||||
|
|
@ -1341,7 +1341,7 @@ GENERATE_PERMUTATIONS_3_EVENTS(irq_read_recursion3_soft_wlock)
|
|||
|
||||
#define I2(x) \
|
||||
do { \
|
||||
raw_spin_lock_init(&lock_##x); \
|
||||
spin_lock_init(&lock_##x); \
|
||||
rwlock_init(&rwlock_##x); \
|
||||
mutex_init(&mutex_##x); \
|
||||
init_rwsem(&rwsem_##x); \
|
||||
|
|
@ -2005,10 +2005,23 @@ static void ww_test_edeadlk_acquire_wrong_slow(void)
|
|||
|
||||
static void ww_test_spin_nest_unlocked(void)
|
||||
{
|
||||
raw_spin_lock_nest_lock(&lock_A, &o.base);
|
||||
spin_lock_nest_lock(&lock_A, &o.base);
|
||||
U(A);
|
||||
}
|
||||
|
||||
/* This is not a deadlock, because we have X1 to serialize Y1 and Y2 */
|
||||
static void ww_test_spin_nest_lock(void)
|
||||
{
|
||||
spin_lock(&lock_X1);
|
||||
spin_lock_nest_lock(&lock_Y1, &lock_X1);
|
||||
spin_lock(&lock_A);
|
||||
spin_lock_nest_lock(&lock_Y2, &lock_X1);
|
||||
spin_unlock(&lock_A);
|
||||
spin_unlock(&lock_Y2);
|
||||
spin_unlock(&lock_Y1);
|
||||
spin_unlock(&lock_X1);
|
||||
}
|
||||
|
||||
static void ww_test_unneeded_slow(void)
|
||||
{
|
||||
WWAI(&t);
|
||||
|
|
@ -2226,6 +2239,10 @@ static void ww_tests(void)
|
|||
dotest(ww_test_spin_nest_unlocked, FAILURE, LOCKTYPE_WW);
|
||||
pr_cont("\n");
|
||||
|
||||
print_testname("spinlock nest test");
|
||||
dotest(ww_test_spin_nest_lock, SUCCESS, LOCKTYPE_WW);
|
||||
pr_cont("\n");
|
||||
|
||||
printk(" -----------------------------------------------------\n");
|
||||
printk(" |block | try |context|\n");
|
||||
printk(" -----------------------------------------------------\n");
|
||||
|
|
|
|||
Loading…
Reference in New Issue