Commit Graph

10 Commits

Author SHA1 Message Date
Will Deacon 398aa66827 ARM: 6212/1: atomic ops: add memory constraints to inline asm
Currently, the 32-bit and 64-bit atomic operations on ARM do not
include memory constraints in the inline assembly blocks. In the
case of barrier-less operations [for example, atomic_add], this
means that the compiler may constant fold values which have actually
been modified by a call to an atomic operation.

This issue can be observed in the atomic64_test routine in
<kernel root>/lib/atomic64_test.c:

00000000 <test_atomic64>:
   0:	e1a0c00d 	mov	ip, sp
   4:	e92dd830 	push	{r4, r5, fp, ip, lr, pc}
   8:	e24cb004 	sub	fp, ip, #4
   c:	e24dd008 	sub	sp, sp, #8
  10:	e24b3014 	sub	r3, fp, #20
  14:	e30d000d 	movw	r0, #53261	; 0xd00d
  18:	e3011337 	movw	r1, #4919	; 0x1337
  1c:	e34c0001 	movt	r0, #49153	; 0xc001
  20:	e34a1aa3 	movt	r1, #43683	; 0xaaa3
  24:	e16300f8 	strd	r0, [r3, #-8]!
  28:	e30c0afe 	movw	r0, #51966	; 0xcafe
  2c:	e30b1eef 	movw	r1, #48879	; 0xbeef
  30:	e34d0eaf 	movt	r0, #57007	; 0xdeaf
  34:	e34d1ead 	movt	r1, #57005	; 0xdead
  38:	e1b34f9f 	ldrexd	r4, [r3]
  3c:	e1a34f90 	strexd	r4, r0, [r3]
  40:	e3340000 	teq	r4, #0
  44:	1afffffb 	bne	38 <test_atomic64+0x38>
  48:	e59f0004 	ldr	r0, [pc, #4]	; 54 <test_atomic64+0x54>
  4c:	e3a0101e 	mov	r1, #30
  50:	ebfffffe 	bl	0 <__bug>
  54:	00000000 	.word	0x00000000

The atomic64_set (0x38-0x44) writes to the atomic64_t, but the
compiler doesn't see this, assumes the test condition is always
false and generates an unconditional branch to __bug. The rest of the
test is optimised away.

This patch adds suitable memory constraints to the atomic operations on ARM
to ensure that the compiler is informed of the correct data hazards. We have
to use the "Qo" constraints to avoid hitting the GCC anomaly described at
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44492 , where the compiler
makes assumptions about the writeback in the addressing mode used by the
inline assembly. These constraints forbid the use of auto{inc,dec} addressing
modes, so it doesn't matter if we don't use the operand exactly once.

Cc: stable@kernel.org
Reviewed-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2010-07-09 11:29:35 +01:00
Will Deacon 068de8d1be ARM: 6211/1: atomic ops: fix register constraints for atomic64_add_unless
The atomic64_add_unless function compares an atomic variable with
a given value and, if they are not equal, adds another given value
to the atomic variable. The function returns zero if the addition
did not occur and non-zero otherwise.

On ARM, the return value is initialised to 1 in C code. Inline assembly
code then performs the atomic64_add_unless operation, setting the
return value to 0 iff the addition does not occur. This means that
when the addition *does* occur, the value of ret must be preserved
across the inline assembly and therefore requires a "+r" constraint
rather than the current one of "=&r".

Thanks to Nicolas Pitre for helping to spot this.

Cc: stable@kernel.org
Reviewed-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2010-07-09 11:29:35 +01:00
Anton Blanchard f3d46f9d31 atomic_t: Cast to volatile when accessing atomic variables
In preparation for removing volatile from the atomic_t definition, this
patch adds a volatile cast to all the atomic read functions.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-05-17 07:57:27 -07:00
Will Deacon 24b44a66fa ARM: 5889/1: Add atomic64 routines for ARMv6k and above.
In preparation for perf-events support, ARM needs to support atomic64_t
operations. v6k and above support the ldrexd and strexd instructions to
do just that.

This patch adds atomic64 support to the ARM architecture. v6k and above
make use of new instructions whilst older cores fall back on the generic
solution using spinlocks. If and when v7-M cores are supported by Linux,
they will need to fall back on the spinlock implementation too.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2010-02-15 21:39:50 +00:00
Catalin Marinas 200b812d00 Clear the exclusive monitor when returning from an exception
The patch adds a CLREX or dummy STREX to the exception return path. This
is needed because several atomic/locking operations use a pair of
LDREX/STREXEQ and the EQ condition may not always be satisfied. This
would leave the exclusive monitor status set and may cause problems with
atomic/locking operations in the interrupted code.

With this patch, the atomic_set() operation can be a simple STR
instruction (on SMP systems, the global exclusive monitor is cleared by
STR anyway). Clearing the exclusive monitor during context switch is no
longer needed as this is handled by the exception return path anyway.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Jamie Lokier <jamie@shareable.org>
2009-09-18 23:30:11 +01:00
Jaswinder Singh Rajput feecaf73bb ARM: includecheck fix: atomic.h
fix the following 'make includecheck' warning:

  arch/arm/include/asm/atomic.h: asm/system.h is included more than once.

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2009-07-25 17:07:01 +01:00
Arnd Bergmann 72099ed271 asm-generic: rename atomic.h to atomic-long.h
The existing asm-generic/atomic.h only defines the
atomic_long type. This renames it to atomic-long.h
so we have a place to add a truly generic atomic.h
that can be used on all non-SMP systems.

Signed-off-by: Remis Lima Baima <remis.developer@googlemail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
2009-06-11 21:02:17 +02:00
Russell King bac4e960b5 [ARM] barriers: improve xchg, bitops and atomic SMP barriers
Mathieu Desnoyers pointed out that the ARM barriers were lacking:

- cmpxchg, xchg and atomic add return need memory barriers on
  architectures which can reorder the relative order in which memory
  read/writes can be seen between CPUs, which seems to include recent
  ARM architectures. Those barriers are currently missing on ARM.

- test_and_xxx_bit were missing SMP barriers.

So put these barriers in.  Provide separate atomic_add/atomic_sub
operations which do not require barriers.

Reported-Reviewed-and-Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2009-05-28 19:39:27 +01:00
Matthew Wilcox ea43546750 atomic_t: unify all arch definitions
The atomic_t type cannot currently be used in some header files because it
would create an include loop with asm/atomic.h.  Move the type definition
to linux/types.h to break the loop.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-01-06 15:59:10 -08:00
Russell King 4baa992243 [ARM] move include/asm-arm to arch/arm/include/asm
Move platform independent header files to arch/arm/include/asm, leaving
those in asm/arch* and asm/plat* alone.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2008-08-02 21:32:35 +01:00