OrgACRN
/
acrn-kernel
mirror of https://github.com/projectacrn/acrn-kernel.git
1
0
Fork 0
Code Issues Releases Wiki Activity

printk: Do not take console lock for console_flush_on_panic() 

Currently console_flush_on_panic() will attempt to acquire the
console lock when flushing the buffer on panic. If it fails to
acquire the lock, it continues anyway because this is the last
chance to get any pending records printed.

The reason why the console lock was attempted at all was to
prevent any other CPUs from acquiring the console lock for
printing while the panic CPU was printing. But as of the
previous commit, non-panic CPUs will no longer attempt to
acquire the console lock in a panic situation. Therefore it is
no longer strictly necessary for a panic CPU to acquire the
console lock.

Avoiding taking the console lock when flushing in panic has
the additional benefit of avoiding possible deadlocks due to
semaphore usage in NMI context (semaphores are not NMI-safe)
and avoiding possible deadlocks if another CPU accesses the
semaphore and is stopped while holding one of the semaphore's
internal spinlocks.

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/20230717194607.145135-5-john.ogness@linutronix.de
This commit is contained in:
John Ogness 2023-07-17 21:52:04 +02:06 committed by Petr Mladek
parent 51a1d258e5
commit eacb04ff3c
1 changed files with 19 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
kernel/printk/printk.c
View File

@ -3118,14 +3118,24 @@ void console_unblank(void)
*/ */
void console_flush_on_panic(enum con_flush_mode mode) void console_flush_on_panic(enum con_flush_mode mode)
{ {
bool handover;
u64 next_seq;
/* /*
* If someone else is holding the console lock, trylock will fail * Ignore the console lock and flush out the messages. Attempting a
* and may_schedule may be set. Ignore and proceed to unlock so * trylock would not be useful because:
* that messages are flushed out. As this can be called from any *
* context and we don't want to get preempted while flushing, * - if it is contended, it must be ignored anyway
* ensure may_schedule is cleared. * - console_lock() and console_trylock() block and fail
* respectively in panic for non-panic CPUs
* - semaphores are not NMI-safe
*/
/*
* If another context is holding the console lock,
* @console_may_schedule might be set. Clear it so that
* this context does not call cond_resched() while flushing.
*/ */
console_trylock();
console_may_schedule = 0; console_may_schedule = 0;
if (mode == CONSOLE_REPLAY_ALL) { if (mode == CONSOLE_REPLAY_ALL) {
@ -3138,15 +3148,15 @@ void console_flush_on_panic(enum con_flush_mode mode)
cookie = console_srcu_read_lock(); cookie = console_srcu_read_lock();
for_each_console_srcu(c) { for_each_console_srcu(c) {
/* /*
* If the above console_trylock() failed, this is an * This is an unsynchronized assignment, but the
* unsynchronized assignment. But in that case, the
* kernel is in "hope and pray" mode anyway. * kernel is in "hope and pray" mode anyway.
*/ */
c->seq = seq; c->seq = seq;
} }
console_srcu_read_unlock(cookie); console_srcu_read_unlock(cookie);
} }
console_unlock();
console_flush_all(false, &next_seq, &handover);
} }
/* /*