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| author |   John Ogness <john.ogness@linutronix.de> | 2024-12-09 12:23:46 +0106 |
|---|---|---|
| committer |   Petr Mladek <pmladek@suse.com> | 2024-12-16 13:26:31 +0100 |
| commit | 0161e2d6950fe66cf6ac1c10d945bae971f33667 (patch) | |
| tree | e12087793cfe89c62446951321929beeb03ae651 | |
| parent | printk: Remove redundant deferred check in vprintk() (diff) | |
| download | linux-rng-0161e2d6950fe66cf6ac1c10d945bae971f33667.tar.xz linux-rng-0161e2d6950fe66cf6ac1c10d945bae971f33667.zip | |
printk: Defer legacy printing when holding printk_cpu_sync
The documentation of printk_cpu_sync_get() clearly states
that the owner must never perform any activities where it waits
for a CPU. For legacy printing there can be spinning on the
console_lock and on the port lock. Therefore legacy printing
must be deferred when holding the printk_cpu_sync.
Note that in the case of emergency states, atomic consoles
are not prevented from printing when printk is deferred. This
is appropriate because they do not spin-wait indefinitely for
other CPUs.
Reported-by: Rik van Riel <riel@surriel.com>
Closes: https://lore.kernel.org/r/20240715232052.73eb7fb1@imladris.surriel.com
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Fixes: 55d6af1d6688 ("lib/nmi_backtrace: explicitly serialize banner and regs")
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20241209111746.192559-3-john.ogness@linutronix.de
Signed-off-by: Petr Mladek <pmladek@suse.com>
| -rw-r--r-- | kernel/printk/internal.h | 6 | ||||
| -rw-r--r-- | kernel/printk/printk.c | 5 | ||||
| -rw-r--r-- | kernel/printk/printk_safe.c | 7 |
3 files changed, 17 insertions, 1 deletions
diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index c6bb47666aef..a91bdf802967 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -338,3 +338,9 @@ bool printk_get_next_message(struct printk_message *pmsg, u64 seq, void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped); void console_prepend_replay(struct printk_message *pmsg); #endif + +#ifdef CONFIG_SMP +bool is_printk_cpu_sync_owner(void); +#else +static inline bool is_printk_cpu_sync_owner(void) { return false; } +#endif diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 80910bc3470c..f446a06b4da8 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -4922,6 +4922,11 @@ void console_try_replay_all(void) static atomic_t printk_cpu_sync_owner = ATOMIC_INIT(-1); static atomic_t printk_cpu_sync_nested = ATOMIC_INIT(0); +bool is_printk_cpu_sync_owner(void) +{ + return (atomic_read(&printk_cpu_sync_owner) == raw_smp_processor_id()); +} + /** * __printk_cpu_sync_wait() - Busy wait until the printk cpu-reentrant * spinning lock is not owned by any CPU. diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c index 6283bc0b55e6..32a28f563b13 100644 --- a/kernel/printk/printk_safe.c +++ b/kernel/printk/printk_safe.c @@ -61,10 +61,15 @@ bool is_printk_legacy_deferred(void) /* * The per-CPU variable @printk_context can be read safely in any * context. CPU migration is always disabled when set. + * + * A context holding the printk_cpu_sync must not spin waiting for + * another CPU. For legacy printing, it could be the console_lock + * or the port lock. */ return (force_legacy_kthread() || this_cpu_read(printk_context) || - in_nmi()); + in_nmi() || + is_printk_cpu_sync_owner()); } asmlinkage int vprintk(const char *fmt, va_list args) |