-----BEGIN PGP SIGNATURE-----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=EUpJ
-----END PGP SIGNATURE-----
Merge tag 'printk-for-5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux
Pull printk updates from Petr Mladek:
- Make %pK behave the same as %p for kptr_restrict == 0 also with
no_hash_pointers parameter
- Ignore the default console in the device tree also when console=null
or console="" is used on the command line
- Document console=null and console="" behavior
- Prevent a deadlock and a livelock caused by console_lock in panic()
- Make console_lock available for panicking CPU
- Fast query for the next to-be-used sequence number
- Use the expected return values in printk.devkmsg __setup handler
- Use the correct atomic operations in wake_up_klogd() irq_work handler
- Avoid possible unaligned access when handling %4cc printing format
* tag 'printk-for-5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
printk: fix return value of printk.devkmsg __setup handler
vsprintf: Fix %pK with kptr_restrict == 0
printk: make suppress_panic_printk static
printk: Set console_set_on_cmdline=1 when __add_preferred_console() is called with user_specified == true
Docs: printk: add 'console=null|""' to admin/kernel-parameters
printk: use atomic updates for klogd work
printk: Drop console_sem during panic
printk: Avoid livelock with heavy printk during panic
printk: disable optimistic spin during panic
printk: Add panic_in_progress helper
vsprintf: Move space out of string literals in fourcc_string()
vsprintf: Fix potential unaligned access
printk: ringbuffer: Improve prb_next_seq() performance
If an invalid option value is used with "printk.devkmsg=<value>",
it is silently ignored.
If a valid option value is used, it is honored but the wrong return
value (0) is used, indicating that the command line option had an
error and was not handled. This string is not added to init's
environment strings due to init/main.c::unknown_bootoption()
checking for a '.' in the boot option string and then considering
that string to be an "Unused module parameter".
Print a warning message if a bad option string is used.
Always return 1 from the __setup handler to indicate that the command
line option has been handled.
Fixes: 750afe7bab ("printk: add kernel parameter to control writes to /dev/kmsg")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: Igor Zhbanov <i.zhbanov@omprussia.ru>
Link: lore.kernel.org/r/64644a2f-4a20-bab3-1e15-3b2cdd0defe3@omprussia.ru
Cc: Borislav Petkov <bp@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: John Ogness <john.ogness@linutronix.de>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220228220556.23484-1-rdunlap@infradead.org
This symbol is not used outside of printk.c, so marks it static.
Fix the following sparse warning:
kernel/printk/printk.c💯19: warning: symbol 'suppress_panic_printk'
was not declared. Should it be static?
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220216031957.9761-1-jiapeng.chong@linux.alibaba.com
In case of using console="" or console=null
set console_set_on_cmdline=1 to disable "stdout-path" node from DT.
We basically need to set it every time when __add_preferred_console()
is called with parameter 'user_specified' set.
Therefore we can move setting it into a helper function that is
called from __add_preferred_console().
Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Andre Kalb <andre.kalb@sma.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/YgzU4ho8l6XapyG2@pc6682
The per-cpu @printk_pending variable can be updated from
sleepable contexts, such as:
get_random_bytes()
warn_unseeded_randomness()
printk_deferred()
defer_console_output()
and can be updated from interrupt contexts, such as:
handle_irq_event_percpu()
__irq_wake_thread()
wake_up_process()
try_to_wake_up()
select_task_rq()
select_fallback_rq()
printk_deferred()
defer_console_output()
and can be updated from NMI contexts, such as:
vprintk()
if (in_nmi()) defer_console_output()
Therefore the atomic variant of the updating functions must be used.
Replace __this_cpu_xchg() with this_cpu_xchg().
Replace __this_cpu_or() with this_cpu_or().
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/87iltld4ue.fsf@jogness.linutronix.de
If another CPU is in panic, we are about to be halted. Try to gracefully
abandon the console_sem, leaving it free for the panic CPU to grab.
Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220202171821.179394-5-stephen.s.brennan@oracle.com
During panic(), if another CPU is writing heavily the kernel log (e.g.
via /dev/kmsg), then the panic CPU may livelock writing out its messages
to the console. Note when too many messages are dropped during panic and
suppress further printk, except from the panic CPU. This could result in
some important messages being dropped. However, messages are already
being dropped, so this approach at least prevents a livelock.
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220202171821.179394-4-stephen.s.brennan@oracle.com
A CPU executing with console lock spinning enabled might be halted
during a panic. Before the panicking CPU calls console_flush_on_panic(),
it may call console_trylock(), which attempts to optimistically spin,
deadlocking the panic CPU:
CPU 0 (panic CPU) CPU 1
----------------- ------
printk() {
vprintk_func() {
vprintk_default() {
vprintk_emit() {
console_unlock() {
console_lock_spinning_enable();
... printing to console ...
panic() {
crash_smp_send_stop() {
NMI -------------------> HALT
}
atomic_notifier_call_chain() {
printk() {
...
console_trylock_spinnning() {
// optimistic spin infinitely
This hang during panic can be induced when a kdump kernel is loaded, and
crash_kexec_post_notifiers=1 is present on the kernel command line. The
following script which concurrently writes to /dev/kmsg, and triggers a
panic, can result in this hang:
#!/bin/bash
date
# 991 chars (based on log buffer size):
chars="$(printf 'a%.0s' {1..991})"
while :; do
echo $chars > /dev/kmsg
done &
echo c > /proc/sysrq-trigger &
date
exit
To avoid this deadlock, ensure that console_trylock_spinning() does not
allow spinning once a panic has begun.
Fixes: dbdda842fe ("printk: Add console owner and waiter logic to load balance console writes")
Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220202171821.179394-3-stephen.s.brennan@oracle.com
This will be used help avoid deadlocks during panics. Although it would
be better to include this in linux/panic.h, it would require that header
to include linux/atomic.h as well. On some architectures, this results
in a circular dependency as well. So instead add the helper directly to
printk.c.
Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220202171821.179394-2-stephen.s.brennan@oracle.com
The move of proc_dointvec_minmax_sysadmin() from kernel/sysctl.c to
kernel/printk/sysctl.c introduced an incorrect __user attribute to the
buffer argument. I spotted this change in [1] as well as the kernel
test robot. Revert this change to please sparse:
kernel/printk/sysctl.c:20:51: warning: incorrect type in argument 3 (different address spaces)
kernel/printk/sysctl.c:20:51: expected void *
kernel/printk/sysctl.c:20:51: got void [noderef] __user *buffer
Fixes: faaa357a55 ("printk: move printk sysctl to printk/sysctl.c")
Link: https://lore.kernel.org/r/20220104155024.48023-2-mic@digikod.net [1]
Reported-by: kernel test robot <lkp@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
Link: https://lore.kernel.org/r/20220203145029.272640-1-mic@digikod.net
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
prb_next_seq() always iterates from the first known sequence number.
In the worst case, it might loop 8k times for 256kB buffer,
15k times for 512kB buffer, and 64k times for 2MB buffer.
It was reported that polling and reading using syslog interface
might occupy 50% of CPU.
Speedup the search by storing @id of the last finalized descriptor.
The loop is still needed because the @id is stored and read in the best
effort way. An atomic variable is used to keep the @id consistent.
But the stores and reads are not serialized against each other.
The descriptor could get reused in the meantime. The related sequence
number will be used only when it is still valid.
An invalid value should be read _only_ when there is a flood of messages
and the ringbuffer is rapidly reused. The performance is the least
problem in this case.
Reported-by: Chunlei Wang <chunlei.wang@mediatek.com>
Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/1642770388-17327-1-git-send-email-quic_mojha@quicinc.com
Link: https://lore.kernel.org/lkml/YXlddJxLh77DKfIO@alley/T/#m43062e8b2a17f8dbc8c6ccdb8851fb0dbaabbb14
build warning when CONFIG_PRINTK=n
kernel/printk/printk.c:175:5: warning: no previous prototype for
'devkmsg_sysctl_set_loglvl' [-Wmissing-prototypes]
devkmsg_sysctl_set_loglvl() is only used in sysctl.c when
CONFIG_PRINTK=y, but it participates in the build when CONFIG_PRINTK=n.
So add compile dependency CONFIG_PRINTK=y && CONFIG_SYSCTL=y to fix the
build warning.
Link: https://lkml.kernel.org/r/20211129211943.640266-5-mcgrof@kernel.org
Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: Antti Palosaari <crope@iki.fi>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Lukas Middendorf <kernel@tuxforce.de>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
Cc: Stephen Kitt <steve@sk2.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/sysctl.c is a kitchen sink where everyone leaves their dirty
dishes, this makes it very difficult to maintain.
To help with this maintenance let's start by moving sysctls to places
where they actually belong. The proc sysctl maintainers do not want to
know what sysctl knobs you wish to add for your own piece of code, we
just care about the core logic.
So move printk sysctl from kernel/sysctl.c to kernel/printk/sysctl.c.
Use register_sysctl() to register the sysctl interface.
[mcgrof@kernel.org: fixed compile issues when PRINTK is not set, commit log update]
Link: https://lkml.kernel.org/r/20211124231435.1445213-6-mcgrof@kernel.org
Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Antti Palosaari <crope@iki.fi>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Clemens Ladisch <clemens@ladisch.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Douglas Gilbert <dgilbert@interlog.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: James E.J. Bottomley <jejb@linux.ibm.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Julia Lawall <julia.lawall@inria.fr>
Cc: Kees Cook <keescook@chromium.org>
Cc: Lukas Middendorf <kernel@tuxforce.de>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Phillip Potter <phil@philpotter.co.uk>
Cc: Qing Wang <wangqing@vivo.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Sebastian Reichel <sre@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Stephen Kitt <steve@sk2.org>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The variable @bcon has two meanings. It is used several times for iterating
the list of registered consoles. In the meantime, it holds the information
whether a boot console is first in @console_drivers list.
The information about the 1st console driver used to be important for
the decision whether to install the new console by default or not.
It allowed to re-evaluate the variable @need_default_console when
a real console with tty binding has been unregistered in the meantime.
The decision about the default console is not longer affected by @bcon
variable. The current code checks whether the first driver is real
and has tty binding directly.
The information about the first console is still used for two more
decisions:
1. It prevents duplicate output on non-boot consoles with
CON_CONSDEV flag set.
2. Early/boot consoles are unregistered when a real console with
CON_CONSDEV is registered and @keep_bootcon is not set.
The behavior in the real life is far from obvious. @bcon is set according
to the first console @console_drivers list. But the first position in
the list is special:
1. Consoles with CON_CONSDEV flag are put at the beginning of
the list. It is either the preferred console or any console
with tty binding registered by default.
2. Another console might become the first in the list when
the first console in the list is unregistered. It might
happen either explicitly or automatically when boot
consoles are unregistered.
There is one more important rule:
+ Boot consoles can't be registered when any real console
is already registered.
It is a puzzle. The main complication is the dependency on the first
position is the list and the complicated rules around it.
Let's try to make it easier:
1. Add variable @bootcon_enabled and set it by iterating all registered
consoles. The variable has obvious meaning and more predictable
behavior. Any speed optimization and other tricks are not worth it.
2. Use a generic name for the variable that is used to iterate
the list on registered console drivers.
Behavior change:
No, maybe surprisingly, there is _no_ behavior change!
Let's provide the proof by contradiction. Both operations, duplicate
output prevention and boot consoles removal, are done only when
the newly added console has CON_CONSDEV flag set. The behavior
would change when the new @bootcon_enabled has different value
than the original @bcon.
By other words, the behavior would change when the following conditions
are true:
+ a console with CON_CONSDEV flag is added
+ a real (non-boot) console is the first in the list
+ a boot console is later in the list
Now, a real console might be first in the list only when:
+ It was the first registered console. In this case, there can't be
any boot console because any later ones were rejected.
+ It was put at the first position because it had CON_CONSDEV flag
set. It was either the preferred console or it was a console with
tty binding registered by default. We are interested only in
a real consoles here. And real console with tty binding fulfills
conditions of the default console.
Now, there is always only one console that is either preferred
or fulfills conditions of the default console. It can't be already
in the list and being registered at the same time.
As a result, the above three conditions could newer be "true" at
the same time. Therefore the behavior can't change.
Final dilemma:
OK, the new code has the same behavior. But is the change in the right
direction? What if the handling of @console_drivers is updated in
the future?
OK, let's look at it from another angle:
1. The ordering of @console_drivers list is important only in
console_device() function. The first console driver with tty
binding gets associated with /dev/console.
2. CON_CONSDEV flag is shown in /proc/consoles. And it should be set
for the driver that is returned by console_device().
3. A boot console is removed and the duplicated output is prevented
when the real console with CON_CONSDEV flag is registered.
Now, in the ideal world:
+ The driver associated with /dev/console should be either a console
preferred via the command line, device tree, or SPCR. Or it should
be the first real console with tty binding registered by default.
+ The code should match the related boot and real console drivers.
It should unregister only the obsolete boot driver. And the duplicated
output should be prevented only on the related real driver.
It is clear that it is not guaranteed by the current code. Instead,
the current code looks like a maze of heuristics that try to achieve
the above.
It is result of adding several features over last few decades. For example,
a possibility to register more consoles, unregister consoles, boot
consoles, consoles without tty binding, device tree, SPCR, braille
consoles.
Anyway, there is no reason why the decision, about removing boot consoles
and preventing duplicated output, should depend on the first console
in the list. The current code does the decisions primary by CON_CONSDEV
flag that is used for the preferred console. It looks like a
good compromise. And the change seems to be in the right direction.
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20211122132649.12737-6-pmladek@suse.com
The variable @need_default_console is used to decide whether a newly
registered console should get enabled by default.
The logic is complicated. It can be modified in a register_console()
call. But it is always re-evaluated in the next call by the following
condition:
if (need_default_console || bcon || !console_drivers)
need_default_console = preferred_console < 0;
In short, the value is updated when either of the condition is valid:
+ the value is still, or again, "true"
+ boot/early console is still the first in @console_driver list
+ @console_driver list is empty
The value is updated according to @preferred_console. In particular,
it is set to "false" when a @preferred_console was set by
__add_preferred_console(). This happens when a non-braille console
was added via the command line, device tree, or SPCR.
It far from clear what this all means together. Let's look at
@need_default_console from another angle:
1. The value is "true" by default. It means that it is always set
according to @preferred_console during the first register_console()
call.
By other words, the first register_console() call will register
the console by default only when none non-braille console was defined
via the command line, device tree, or SPCR.
2. The value will always stay "false" when @preferred_console is set.
By other words, try_enable_default_console() will never get called
when a non-braille console is explicitly required.
4. The value might be set to "false" in try_enable_default_console()
when a console with tty binding (driver) gets enabled.
In this case CON_CONSDEV is set as well. It causes that the console
will be inserted as first into the list @console_driver. It might
be either real or boot/early console.
5. The value will be set _back_ to "true" in the next register_console()
call when:
+ The console added by the previous register_console() had been
a boot/early one.
+ The last console has been unregistered in the meantime and
a boot/early console became first in @console_drivers list
again. Or the list became empty.
By other words, the value will stay "false" only when the last
registered console was real, had tty binding, and was not removed
in the mean time.
The main logic looks clear:
+ Consoles are enabled by default only when no one is preferred
via the command line, device tree, or SPCR.
+ By default, any console is enabled until a real console
with tty binding gets registered.
The behavior when the real console with tty binding is later removed
is a bit unclear:
+ By default, any new console is registered again only when there
is no console or the first console in the list is a boot one.
The question is why the code is suddenly happy when a real console
without tty binding is the first in the list. It looks like an overlook
and bug.
Conclusion:
The state of @preferred_console and the first console in @console_driver
list should be enough to decide whether we need to enable the given console
by default.
The rules are simple. New consoles are _not_ enabled by default
when either of the following conditions is true:
+ @preferred_console is set. It means that a non-braille console
is explicitly configured via the command line, device tree, or SPCR.
+ A real console with tty binding is registered. Such a console will
have CON_CONSDEV flag set and will always be the first in
@console_drivers list.
Note:
The new code does not use @bcon variable. The meaning of the variable
is far from clear. The direct check of the first console in the list
makes it more clear that only real console fulfills requirements
of the default console.
Behavior change:
As already discussed above. There was one situation where the original
code worked a strange way. Let's have:
+ console A: real console without tty binding
+ console B: real console with tty binding
and do:
register_console(A); /* 1st step */
register_console(B); /* 2nd step */
unregister_console(B); /* 3rd step */
register_console(B); /* 4th step */
The original code will not register the console B in the 4th step.
@need_default_console is set to "false" in 2nd step. The real console
with tty binding (driver) is then removed in the 3rd step.
But @need_default_console will stay "false" in the 4th step because
there is no boot/early console and @registered_consoles list is not
empty.
The new code will register the console B in the 4th step because
it checks whether the first console has tty binding (->driver)
This behavior change should acceptable:
1. The scenario requires manual intervention (console removal).
The system should boot with the same consoles as before.
2. Console B is registered again probably because the user wants
to use it. The most likely scenario is that the related
module is reloaded.
3. It makes the behavior more consistent and predictable.
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20211122132649.12737-5-pmladek@suse.com
There is no need to clear @need_default_console when a console
preferred by the command line, device tree, or SPCR, gets enabled.
The code is called only when some non-braille console matched a console
in @console_cmdline array. It means that a non-braille console was added
in __add_preferred_console() and the variable preferred_console is set
to a number >= 0. As a result, @need_default_console is always set to
"false" in the magic condition:
if (need_default_console || bcon || !console_drivers)
need_default_console = preferred_console < 0;
This is one small step in removing the above magic condition
that is hard to follow.
The patch removes one superfluous assignment and should not change
the functionality.
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20211122132649.12737-4-pmladek@suse.com
The logic around the variable @has_preferred_console made my head
spin many times. Part of the problem is the ambiguous name.
There is the variable @preferred_console. It points to the last
non-braille console in @console_cmdline array. This array contains
consoles preferred via the command line, device tree, or SPCR.
Then there is the variable @has_preferred_console. It is set to
"true" when @preferred_console is enabled or when a console with
tty binding gets enabled by default.
It might get reset back by the magic condition:
if (!has_preferred_console || bcon || !console_drivers)
has_preferred_console = preferred_console >= 0;
It is a puzzle. Dumb explanation is that it gets re-evaluated
when:
+ it was not set before (see above when it gets set)
+ there is still an early console enabled (bcon)
+ there is no console enabled (!console_drivers)
This is still a puzzle.
It gets more clear when we see where the value is checked. The only
meaning of the variable is to decide whether we should try to enable
the new console by default.
Rename the variable according to the single situation where
the value is checked.
The rename requires an inverted logic. Otherwise, it is a simple
search & replace. It does not change the functionality.
Signed-off-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Link: https://lore.kernel.org/r/20211122132649.12737-3-pmladek@suse.com
Put the code enabling a console by default into a separate function
called try_enable_default_console().
Rename try_enable_new_console() to try_enable_preferred_console() to
make the purpose of the different variants more clear.
It is a code refactoring without any functional change.
Signed-off-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Link: https://lore.kernel.org/r/20211122132649.12737-2-pmladek@suse.com
-----BEGIN PGP SIGNATURE-----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=wbBy
-----END PGP SIGNATURE-----
Merge tag 'printk-for-5.16-fixup' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux
Pull printk fixes from Petr Mladek:
- Try to flush backtraces from other CPUs also on the local one. This
was a regression caused by printk_safe buffers removal.
- Remove header dependency warning.
* tag 'printk-for-5.16-fixup' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
printk: Remove printk.h inclusion in percpu.h
printk: restore flushing of NMI buffers on remote CPUs after NMI backtraces
printk from NMI context relies on irq work being raised on the local CPU
to print to console. This can be a problem if the NMI was raised by a
lockup detector to print lockup stack and regs, because the CPU may not
enable irqs (because it is locked up).
Introduce printk_trigger_flush() that can be called another CPU to try
to get those messages to the console, call that where printk_safe_flush
was previously called.
Fixes: 93d102f094 ("printk: remove safe buffers")
Cc: stable@vger.kernel.org # 5.15
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20211107045116.1754411-1-npiggin@gmail.com
Merge misc updates from Andrew Morton:
"257 patches.
Subsystems affected by this patch series: scripts, ocfs2, vfs, and
mm (slab-generic, slab, slub, kconfig, dax, kasan, debug, pagecache,
gup, swap, memcg, pagemap, mprotect, mremap, iomap, tracing, vmalloc,
pagealloc, memory-failure, hugetlb, userfaultfd, vmscan, tools,
memblock, oom-kill, hugetlbfs, migration, thp, readahead, nommu, ksm,
vmstat, madvise, memory-hotplug, rmap, zsmalloc, highmem, zram,
cleanups, kfence, and damon)"
* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (257 commits)
mm/damon: remove return value from before_terminate callback
mm/damon: fix a few spelling mistakes in comments and a pr_debug message
mm/damon: simplify stop mechanism
Docs/admin-guide/mm/pagemap: wordsmith page flags descriptions
Docs/admin-guide/mm/damon/start: simplify the content
Docs/admin-guide/mm/damon/start: fix a wrong link
Docs/admin-guide/mm/damon/start: fix wrong example commands
mm/damon/dbgfs: add adaptive_targets list check before enable monitor_on
mm/damon: remove unnecessary variable initialization
Documentation/admin-guide/mm/damon: add a document for DAMON_RECLAIM
mm/damon: introduce DAMON-based Reclamation (DAMON_RECLAIM)
selftests/damon: support watermarks
mm/damon/dbgfs: support watermarks
mm/damon/schemes: activate schemes based on a watermarks mechanism
tools/selftests/damon: update for regions prioritization of schemes
mm/damon/dbgfs: support prioritization weights
mm/damon/vaddr,paddr: support pageout prioritization
mm/damon/schemes: prioritize regions within the quotas
mm/damon/selftests: support schemes quotas
mm/damon/dbgfs: support quotas of schemes
...
Rename memblock_free_ptr() to memblock_free() and use memblock_free()
when freeing a virtual pointer so that memblock_free() will be a
counterpart of memblock_alloc()
The callers are updated with the below semantic patch and manual
addition of (void *) casting to pointers that are represented by
unsigned long variables.
@@
identifier vaddr;
expression size;
@@
(
- memblock_phys_free(__pa(vaddr), size);
+ memblock_free(vaddr, size);
|
- memblock_free_ptr(vaddr, size);
+ memblock_free(vaddr, size);
)
[sfr@canb.auug.org.au: fixup]
Link: https://lkml.kernel.org/r/20211018192940.3d1d532f@canb.auug.org.au
Link: https://lkml.kernel.org/r/20210930185031.18648-7-rppt@kernel.org
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Juergen Gross <jgross@suse.com>
Cc: Shahab Vahedi <Shahab.Vahedi@synopsys.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-----BEGIN PGP SIGNATURE-----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=t12m
-----END PGP SIGNATURE-----
Merge tag 'printk-for-5.16' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux
Pull printk updates from Petr Mladek:
- Extend %pGp print format to print hex value of the page flags
- Use kvmalloc instead of kmalloc to allocate devkmsg buffers
- Misc cleanup and warning fixes
* tag 'printk-for-5.16' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
vsprintf: Update %pGp documentation about that it prints hex value
lib/vsprintf.c: Amend static asserts for format specifier flags
vsprintf: Make %pGp print the hex value
test_printf: Append strings more efficiently
test_printf: Remove custom appending of '|'
test_printf: Remove separate page_flags variable
test_printf: Make pft array const
ia64: don't do IA64_CMPXCHG_DEBUG without CONFIG_PRINTK
printk: use gnu_printf format attribute for printk_sprint()
printk: avoid -Wsometimes-uninitialized warning
printk: use kvmalloc instead of kmalloc for devkmsg_user
Fix the following W=1 kernel build warning:
kernel/printk/printk.c: In function 'printk_sprint':
kernel/printk/printk.c:1913:9: warning: function 'printk_sprint' might be
a candidate for 'gnu_printf' format attribute [-Wsuggest-attribute=format]
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210927142203.124730-1-john.ogness@linutronix.de
clang notices that the pi_get_entry() function would use
uninitialized data if it was called with a non-NULL module
pointer on a kernel that does not support modules:
kernel/printk/index.c:32:6: error: variable 'nr_entries' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
if (!mod) {
^~~~
kernel/printk/index.c:38:13: note: uninitialized use occurs here
if (pos >= nr_entries)
^~~~~~~~~~
kernel/printk/index.c:32:2: note: remove the 'if' if its condition is always true
if (!mod) {
Rework the condition to make it clear to the compiler that we are always
in the second case. Unfortunately the #ifdef is still required as the
definition of 'struct module' is hidden when modules are disabled.
Fixes: 3370155737 ("printk: Userspace format indexing support")
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210928093456.2438109-1-arnd@kernel.org
The boot-time allocation interface for memblock is a mess, with
'memblock_alloc()' returning a virtual pointer, but then you are
supposed to free it with 'memblock_free()' that takes a _physical_
address.
Not only is that all kinds of strange and illogical, but it actually
causes bugs, when people then use it like a normal allocation function,
and it fails spectacularly on a NULL pointer:
https://lore.kernel.org/all/20210912140820.GD25450@xsang-OptiPlex-9020/
or just random memory corruption if the debug checks don't catch it:
https://lore.kernel.org/all/61ab2d0c-3313-aaab-514c-e15b7aa054a0@suse.cz/
I really don't want to apply patches that treat the symptoms, when the
fundamental cause is this horribly confusing interface.
I started out looking at just automating a sane replacement sequence,
but because of this mix or virtual and physical addresses, and because
people have used the "__pa()" macro that can take either a regular
kernel pointer, or just the raw "unsigned long" address, it's all quite
messy.
So this just introduces a new saner interface for freeing a virtual
address that was allocated using 'memblock_alloc()', and that was kept
as a regular kernel pointer. And then it converts a couple of users
that are obvious and easy to test, including the 'xbc_nodes' case in
lib/bootconfig.c that caused problems.
Reported-by: kernel test robot <oliver.sang@intel.com>
Fixes: 40caa127f3 ("init: bootconfig: Remove all bootconfig data when the init memory is removed")
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
If CONFIG_MODULES is n, we got this:
kernel/printk/index.c:146:13: warning: ‘pi_remove_file’ defined but not used [-Wunused-function]
Move it inside #ifdef block to fix this warning.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210804130105.18732-1-yuehaibing@huawei.com
console_verbose() increases console loglevel to
CONSOLE_LOGLEVEL_MOTORMOUTH, which provides more information
to debug a panic/oops.
Unfortunately, in Arista we maintain some DUTs (Device Under Test) that
are configured to have 9600 baud rate. While verbose console messages
have their value to post-analyze crashes, on such setup they:
- may prevent panic/oops messages being printed
- take too long to flush on console resulting in watchdog reboot
In all our setups we use kdump which saves dmesg buffer after panic,
so in reality those extra messages on console provide no additional value,
but rather add risk of not getting to __crash_kexec().
Provide printk.console_no_auto_verbose boot parameter, which allows
to switch off printk being verbose on oops/panic/lockdep.
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Suggested-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210727130635.675184-3-dima@arista.com
Syslog's SYSLOG_ACTION_READ is supposed to block until the next
syslog record can be read, and then it should read that record.
However, because @syslog_lock is not held between waking up and
reading the record, another reader could read the record first,
thus causing SYSLOG_ACTION_READ to return with a value of 0, never
having read _anything_.
By holding @syslog_lock between waking up and reading, it can be
guaranteed that SYSLOG_ACTION_READ blocks until it successfully
reads a syslog record (or a real error occurs).
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210715193359.25946-7-john.ogness@linutronix.de
@syslog_lock was a raw_spin_lock to simplify the transition of
removing @logbuf_lock and the safe buffers. With that transition
complete, and since all uses of @syslog_lock are within sleepable
contexts, @syslog_lock can become a mutex.
Note that until now register_console() would disable interrupts
using irqsave, which implies that it may be called with interrupts
disabled. And indeed, there is one possible call chain on parisc
where this happens:
handle_interruption(code=1) /* High-priority machine check (HPMC) */
pdc_console_restart()
pdc_console_init_force()
register_console()
However, register_console() calls console_lock(), which might sleep.
So it has never been allowed to call register_console() from an
atomic context and the above call chain is a bug.
Note that the removal of read_syslog_seq_irq() is slightly changing
the behavior of SYSLOG_ACTION_READ by testing against a possibly
outdated @seq value. However, the value of @seq could have changed
after the test, so it is not a new window. A follow-up commit closes
this window.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210715193359.25946-6-john.ogness@linutronix.de
All NMI contexts are handled the same as the safe context: store the
message and defer printing. There is no need to have special NMI
context tracking for this. Using in_nmi() is enough.
There are several parts of the kernel that are manually calling into
the printk NMI context tracking in order to cause general printk
deferred printing:
arch/arm/kernel/smp.c
arch/powerpc/kexec/crash.c
kernel/trace/trace.c
For arm/kernel/smp.c and powerpc/kexec/crash.c, provide a new
function pair printk_deferred_enter/exit that explicitly achieves the
same objective.
For ftrace, remove the printk context manipulation completely. It was
added in commit 03fc7f9c99 ("printk/nmi: Prevent deadlock when
accessing the main log buffer in NMI"). The purpose was to enforce
storing messages directly into the ring buffer even in NMI context.
It really should have only modified the behavior in NMI context.
There is no need for a special behavior any longer. All messages are
always stored directly now. The console deferring is handled
transparently in vprintk().
Signed-off-by: John Ogness <john.ogness@linutronix.de>
[pmladek@suse.com: Remove special handling in ftrace.c completely.
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210715193359.25946-5-john.ogness@linutronix.de
With @logbuf_lock removed, the high level printk functions for
storing messages are lockless. Messages can be stored from any
context, so there is no need for the NMI and safe buffers anymore.
Remove the NMI and safe buffers.
Although the safe buffers are removed, the NMI and safe context
tracking is still in place. In these contexts, store the message
immediately but still use irq_work to defer the console printing.
Since printk recursion tracking is in place, safe context tracking
for most of printk is not needed. Remove it. Only safe context
tracking relating to the console and console_owner locks is left
in place. This is because the console and console_owner locks are
needed for the actual printing.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210715193359.25946-4-john.ogness@linutronix.de
Currently the printk safe buffers provide a form of recursion
protection by redirecting to the safe buffers whenever printk() is
recursively called.
In preparation for removal of the safe buffers, provide an alternate
explicit recursion protection. Recursion is limited to 3 levels
per-CPU and per-context.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210715193359.25946-3-john.ogness@linutronix.de
Commit 3370155737 ("printk: Userspace format indexing support") turned
printk() into a macro, but left the kerneldoc comment for it with the (now)
_printk() function, resulting in this docs-build warning:
kernel/printk/printk.c:1: warning: 'printk' not found
Move the kerneldoc comment back next to the (now) macro it's meant to
describe and have the docs build find it there.
Fixes: 3370155737 ("printk: Userspace format indexing support")
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/87o8aqt7qn.fsf@meer.lwn.net
The commit 3370155737 ("printk: Userspace format indexing support")
triggered the following build failure:
kernel/printk/index.c:140:6: warning: no previous prototype for ‘pi_create_file’ [-Wmissing-prototypes]
void pi_create_file(struct module *mod)
^~~~~~~~~~~~~~
kernel/printk/index.c:146:6: warning: no previous prototype for ‘pi_remove_file’ [-Wmissing-prototypes]
void pi_remove_file(struct module *mod)
^~~~~~~~~~~~~~
Fixes: 3370155737 ("printk: Userspace format indexing support")
Reported-by: kernel test robot <lkp@intel.com>
Suggested-by: Chris Down <chris@chrisdown.name>
[pmladek@suse.com: Let the compiler decide about inlining.]
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/lkml/YPql089IwSpudw%2F1@alley/
We have a number of systems industry-wide that have a subset of their
functionality that works as follows:
1. Receive a message from local kmsg, serial console, or netconsole;
2. Apply a set of rules to classify the message;
3. Do something based on this classification (like scheduling a
remediation for the machine), rinse, and repeat.
As a couple of examples of places we have this implemented just inside
Facebook, although this isn't a Facebook-specific problem, we have this
inside our netconsole processing (for alarm classification), and as part
of our machine health checking. We use these messages to determine
fairly important metrics around production health, and it's important
that we get them right.
While for some kinds of issues we have counters, tracepoints, or metrics
with a stable interface which can reliably indicate the issue, in order
to react to production issues quickly we need to work with the interface
which most kernel developers naturally use when developing: printk.
Most production issues come from unexpected phenomena, and as such
usually the code in question doesn't have easily usable tracepoints or
other counters available for the specific problem being mitigated. We
have a number of lines of monitoring defence against problems in
production (host metrics, process metrics, service metrics, etc), and
where it's not feasible to reliably monitor at another level, this kind
of pragmatic netconsole monitoring is essential.
As one would expect, monitoring using printk is rather brittle for a
number of reasons -- most notably that the message might disappear
entirely in a new version of the kernel, or that the message may change
in some way that the regex or other classification methods start to
silently fail.
One factor that makes this even harder is that, under normal operation,
many of these messages are never expected to be hit. For example, there
may be a rare hardware bug which one wants to detect if it was to ever
happen again, but its recurrence is not likely or anticipated. This
precludes using something like checking whether the printk in question
was printed somewhere fleetwide recently to determine whether the
message in question is still present or not, since we don't anticipate
that it should be printed anywhere, but still need to monitor for its
future presence in the long-term.
This class of issue has happened on a number of occasions, causing
unhealthy machines with hardware issues to remain in production for
longer than ideal. As a recent example, some monitoring around
blk_update_request fell out of date and caused semi-broken machines to
remain in production for longer than would be desirable.
Searching through the codebase to find the message is also extremely
fragile, because many of the messages are further constructed beyond
their callsite (eg. btrfs_printk and other module-specific wrappers,
each with their own functionality). Even if they aren't, guessing the
format and formulation of the underlying message based on the aesthetics
of the message emitted is not a recipe for success at scale, and our
previous issues with fleetwide machine health checking demonstrate as
much.
This provides a solution to the issue of silently changed or deleted
printks: we record pointers to all printk format strings known at
compile time into a new .printk_index section, both in vmlinux and
modules. At runtime, this can then be iterated by looking at
<debugfs>/printk/index/<module>, which emits the following format, both
readable by humans and able to be parsed by machines:
$ head -1 vmlinux; shuf -n 5 vmlinux
# <level[,flags]> filename:line function "format"
<5> block/blk-settings.c:661 disk_stack_limits "%s: Warning: Device %s is misaligned\n"
<4> kernel/trace/trace.c:8296 trace_create_file "Could not create tracefs '%s' entry\n"
<6> arch/x86/kernel/hpet.c:144 _hpet_print_config "hpet: %s(%d):\n"
<6> init/do_mounts.c:605 prepare_namespace "Waiting for root device %s...\n"
<6> drivers/acpi/osl.c:1410 acpi_no_auto_serialize_setup "ACPI: auto-serialization disabled\n"
This mitigates the majority of cases where we have a highly-specific
printk which we want to match on, as we can now enumerate and check
whether the format changed or the printk callsite disappeared entirely
in userspace. This allows us to catch changes to printks we monitor
earlier and decide what to do about it before it becomes problematic.
There is no additional runtime cost for printk callers or printk itself,
and the assembly generated is exactly the same.
Signed-off-by: Chris Down <chris@chrisdown.name>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kees Cook <keescook@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Reported-by: kernel test robot <lkp@intel.com>
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Jessica Yu <jeyu@kernel.org> # for module.{c,h}
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/e42070983637ac5e384f17fbdbe86d19c7b212a5.1623775748.git.chris@chrisdown.name
parse_prefix is needed externally by later patches, so move it into a
context where it can be used as such. Also give it the printk_ prefix to
reduce the chance of collisions.
Signed-off-by: Chris Down <chris@chrisdown.name>
Cc: Petr Mladek <pmladek@suse.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/b22ba314a860e5c7f887958f1eab2649f9bd1d06.1623775748.git.chris@chrisdown.name
In the past, `enum log_flags` was part of `struct log`, hence the name.
`struct log` has since been reworked and now this struct is stored
inside `struct printk_info`. However, the name was never updated, which
is somewhat confusing -- especially since these flags operate at the
record level rather than at the level of an abstract log.
printk_info_flags also joins its other metadata struct friends in
printk_ringbuffer.h.
Signed-off-by: Chris Down <chris@chrisdown.name>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/3dd801982f02603e6e3aa4f8bc4f5ebb830a4949.1623775748.git.chris@chrisdown.name
The standard printk() tries to flush the message to the console
immediately. It tries to take the console lock. If the lock is
already taken then the current owner is responsible for flushing
even the new message.
There is a small race window between checking whether a new message is
available and releasing the console lock. It is solved by re-checking
the state after releasing the console lock. If the check is positive
then console_unlock() tries to take the lock again and process the new
message as well.
The commit 996e966640 ("printk: remove logbuf_lock") causes that
console_seq is not longer read atomically. As a result, the re-check might
be done with an inconsistent 64-bit index.
Solve it by using the last sequence number that has been checked under
the console lock. In the worst case, it will take the lock again only
to realized that the new message has already been proceed. But it
was possible even before.
The variable next_seq is marked as __maybe_unused to call down compiler
warning when CONFIG_PRINTK is not defined.
Fixes: commit 996e966640 ("printk: remove logbuf_lock")
Reported-by: kernel test robot <lkp@intel.com> # unused next_seq warning
Cc: stable@vger.kernel.org # 5.13
Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Link: https://lore.kernel.org/r/20210702150657.26760-1-pmladek@suse.com
-----BEGIN PGP SIGNATURE-----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=Oa1c
-----END PGP SIGNATURE-----
Merge tag 'printk-for-5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux
Pull printk updates from Petr Mladek:
- Add %pt[RT]s modifier to vsprintf(). It overrides ISO 8601 separator
by using ' ' (space). It produces "YYYY-mm-dd HH:MM:SS" instead of
"YYYY-mm-ddTHH:MM:SS".
- Correctly parse long row of numbers by sscanf() when using the field
width. Add extensive sscanf() selftest.
- Generalize re-entrant CPU lock that has already been used to
serialize dump_stack() output. It is part of the ongoing printk
rework. It will allow to remove the obsoleted printk_safe buffers and
introduce atomic consoles.
- Some code clean up and sparse warning fixes.
* tag 'printk-for-5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
printk: fix cpu lock ordering
lib/dump_stack: move cpu lock to printk.c
printk: Remove trailing semicolon in macros
random32: Fix implicit truncation warning in prandom_seed_state()
lib: test_scanf: Remove pointless use of type_min() with unsigned types
selftests: lib: Add wrapper script for test_scanf
lib: test_scanf: Add tests for sscanf number conversion
lib: vsprintf: Fix handling of number field widths in vsscanf
lib: vsprintf: scanf: Negative number must have field width > 1
usb: host: xhci-tegra: Switch to use %ptTs
nilfs2: Switch to use %ptTs
kdb: Switch to use %ptTs
lib/vsprintf: Allow to override ISO 8601 date and time separator
The cpu lock implementation uses a full memory barrier to take
the lock, but no memory barriers when releasing the lock. This
means that changes performed by a lock owner may not be seen by
the next lock owner. This may have been "good enough" for use
by dump_stack() as a serialization mechanism, but it is not
enough to provide proper protection for a critical section.
Correct this problem by using acquire/release memory barriers
for lock/unlock, respectively.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210617095051.4808-3-john.ogness@linutronix.de
dump_stack() implements its own cpu-reentrant spinning lock to
best-effort serialize stack traces in the printk log. However,
there are other functions (such as show_regs()) that can also
benefit from this serialization.
Move the cpu-reentrant spinning lock (cpu lock) into new helper
functions printk_cpu_lock_irqsave()/printk_cpu_unlock_irqrestore()
so that it is available for others as well. For !CONFIG_SMP the
cpu lock is a NOP.
Note that having multiple cpu locks in the system can easily
lead to deadlock. Code needing a cpu lock should use the
printk cpu lock, since the printk cpu lock could be acquired
from any code and any context.
Also note that it is not necessary for a cpu lock to disable
interrupts. However, in upcoming work this cpu lock will be used
for emergency tasks (for example, atomic consoles during kernel
crashes) and any interruptions while holding the cpu lock should
be avoided if possible.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
[pmladek@suse.com: Backported on top of 5.13-rc1.]
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210617095051.4808-2-john.ogness@linutronix.de
Commit 28e1745b9f ("printk: rename vprintk_func to vprintk") while
improving readability by removing vprintk indirection, inadvertently
placed the EXPORT_SYMBOL() for the newly renamed function at the end
of the file.
For reader sanity, and as is convention move the EXPORT_SYMBOL()
declaration just after the end of the function.
Fixes: 28e1745b9f ("printk: rename vprintk_func to vprintk")
Signed-off-by: Punit Agrawal <punitagrawal@gmail.com>
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210614235635.887365-1-punitagrawal@gmail.com
Linus Torvalds