6.8-stable review patch. If anyone has any objections, please let me know.
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From: John Ogness john.ogness@linutronix.de
[ Upstream commit 7412dc6d55eed6b76180e40ac3601412ebde29bd ]
dump_stack() is called in panic(). If for some reason another CPU is holding the printk_cpu_sync and is unable to release it, the panic CPU will be unable to continue and print the stacktrace.
Since non-panic CPUs are not allowed to store new printk messages anyway, there is no need to synchronize the stacktrace output in a panic situation.
For the panic CPU, do not get the printk_cpu_sync because it is not needed and avoids a potential deadlock scenario in panic().
Link: https://lore.kernel.org/lkml/ZcIGKU8sxti38Kok@alley Signed-off-by: John Ogness john.ogness@linutronix.de Reviewed-by: Petr Mladek pmladek@suse.com Link: https://lore.kernel.org/r/20240207134103.1357162-15-john.ogness@linutronix.d... Signed-off-by: Petr Mladek pmladek@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/printk.h | 2 ++ kernel/printk/internal.h | 1 - lib/dump_stack.c | 16 +++++++++++++--- 3 files changed, 15 insertions(+), 4 deletions(-)
diff --git a/include/linux/printk.h b/include/linux/printk.h index 8ef499ab3c1ed..955e31860095e 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -273,6 +273,8 @@ static inline void printk_trigger_flush(void) } #endif
+bool this_cpu_in_panic(void); + #ifdef CONFIG_SMP extern int __printk_cpu_sync_try_get(void); extern void __printk_cpu_sync_wait(void); diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index ac2d9750e5f81..6c2afee5ef620 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -130,7 +130,6 @@ struct printk_message { };
bool other_cpu_in_panic(void); -bool this_cpu_in_panic(void); bool printk_get_next_message(struct printk_message *pmsg, u64 seq, bool is_extended, bool may_supress);
diff --git a/lib/dump_stack.c b/lib/dump_stack.c index 83471e81501a7..222c6d6c8281a 100644 --- a/lib/dump_stack.c +++ b/lib/dump_stack.c @@ -96,15 +96,25 @@ static void __dump_stack(const char *log_lvl) */ asmlinkage __visible void dump_stack_lvl(const char *log_lvl) { + bool in_panic = this_cpu_in_panic(); unsigned long flags;
/* * Permit this cpu to perform nested stack dumps while serialising - * against other CPUs + * against other CPUs, unless this CPU is in panic. + * + * When in panic, non-panic CPUs are not permitted to store new + * printk messages so there is no need to synchronize the output. + * This avoids potential deadlock in panic() if another CPU is + * holding and unable to release the printk_cpu_sync. */ - printk_cpu_sync_get_irqsave(flags); + if (!in_panic) + printk_cpu_sync_get_irqsave(flags); + __dump_stack(log_lvl); - printk_cpu_sync_put_irqrestore(flags); + + if (!in_panic) + printk_cpu_sync_put_irqrestore(flags); } EXPORT_SYMBOL(dump_stack_lvl);