On 2022-02-18 18:29:01 [+0100], Jann Horn wrote: …
Lockdep probably never caught the problem because it's very rare that you actually hit the contended case, and lockdep can't check a
I appears that after ´a' a few words would follow.
Fixes: ea84b580b955 ("pstore: Convert buf_lock to semaphore") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn jannh@google.com
Testing on 5.15.24 (latest stable), with CONFIG_PREEMPT=y, when I trigger a BUG() via LKDTM ("echo BUG > /sys/kernel/debug/provoke-crash/DIRECT"), I first get the expected BUG splat, followed by this RCU warning:
Voluntary context switch within RCU read-side critical section!
Right, scheduling not allowed within a RCU read-side section. I'm not sure if lockdep cares but if you enable CONFIG_DEBUG_ATOMIC_SLEEP then the might_sleep() will complain if you are in a RCU section.
This patch makes the RCU context warning go away.
Makes sense. Acked-by: Sebastian Andrzej Siewior bigeasy@linutronix.de
--- a/fs/pstore/platform.c +++ b/fs/pstore/platform.c @@ -143,27 +143,26 @@ static void pstore_timer_kick(void) mod_timer(&pstore_timer, jiffies + msecs_to_jiffies(pstore_update_ms)); } -/*
- Should pstore_dump() wait for a concurrent pstore_dump()? If
- not, the current pstore_dump() will report a failure to dump
- and return.
- */
-static bool pstore_cannot_wait(enum kmsg_dump_reason reason) +bool pstore_cannot_block_path(enum kmsg_dump_reason reason) {
- /* In NMI path, pstore shouldn't block regardless of reason. */
- /*
* In case of NMI path, pstore shouldn't be blocked* regardless of reason.*/switch (reason) { /* In panic case, other cpus are stopped by smp_send_stop(). */ case KMSG_DUMP_PANIC:
- /* Emergency restart shouldn't be blocked. */
- /* Emergency restart shouldn't be blocked by spin lock. */
by spinning on pstore_info::buf_lock
case KMSG_DUMP_EMERG: return true; default: return false; } } +EXPORT_SYMBOL_GPL(pstore_cannot_block_path); #if IS_ENABLED(CONFIG_PSTORE_DEFLATE_COMPRESS) static int zbufsize_deflate(size_t size)
Sebastian