Commit 7412dc6d authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

dump_stack: Do not get cpu_sync for panic CPU 

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: default avatarJohn Ogness <john.ogness@linutronix.de>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20240207134103.1357162-15-john.ogness@linutronix.de


Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
parent d988d9a9

include/linux/printk.h

+2 −0
Original line number Diff line number Diff line
@@ -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);

kernel/printk/internal.h

+0 −1
Original line number Diff line number Diff line
@@ -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);

lib/dump_stack.c

+13 −3
Original line number Diff line number Diff line
@@ -96,14 +96,24 @@ 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.

	 */

	if (!in_panic)

		printk_cpu_sync_get_irqsave(flags);



	__dump_stack(log_lvl);



	if (!in_panic)

		printk_cpu_sync_put_irqrestore(flags);

}

EXPORT_SYMBOL(dump_stack_lvl);