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@xxxxxxxxxxxxxxx
> Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxx>
> --- 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.
> + */
> if (in_nmi())
> return true;
>
> 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
