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: 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.de
Signed-off-by: Petr Mladek <pmladek@suse.com>
diff --git a/lib/dump_stack.c b/lib/dump_stack.c
index 83471e8..222c6d6 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);
