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printk/panic: Allow cpu backtraces to be written into ringbuffer during panic

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commit 779dbc2e78 ("printk: Avoid non-panic CPUs writing
to ringbuffer") disabled non-panic CPUs to further write messages to
ringbuffer after panicked.

Since the commit, non-panicked CPU's are not allowed to write to
ring buffer after panicked and CPU backtrace which is triggered
after panicked to sample non-panicked CPUs' backtrace no longer
serves its function as it has nothing to print.

Fix the issue by allowing non-panicked CPUs to write into ringbuffer
while CPU backtrace is in flight.

Fixes: 779dbc2e78 ("printk: Avoid non-panic CPUs writing to ringbuffer")
Signed-off-by: Ryo Takakura <takakura@valinux.co.jp>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20240812072703.339690-1-takakura@valinux.co.jp
Signed-off-by: Petr Mladek <pmladek@suse.com>
This commit is contained in:
Ryo Takakura 2024-08-12 16:27:03 +09:00 committed by Petr Mladek
parent 8bf100092d
commit bcc954c6ca
3 changed files with 9 additions and 2 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

1
include/linux/panic.h
View file

@ -16,6 +16,7 @@ extern void oops_enter(void);
extern void oops_exit(void);
extern bool oops_may_print(void);
extern bool panic_triggering_all_cpu_backtrace;
extern int panic_timeout;
extern unsigned long panic_print;
extern int panic_on_oops;

8
kernel/panic.c
View file

@ -64,6 +64,8 @@ unsigned long panic_on_taint;
bool panic_on_taint_nousertaint = false;
static unsigned int warn_limit __read_mostly;
bool panic_triggering_all_cpu_backtrace;
int panic_timeout = CONFIG_PANIC_TIMEOUT;
EXPORT_SYMBOL_GPL(panic_timeout);
@ -253,8 +255,12 @@ void check_panic_on_warn(const char *origin)
*/
static void panic_other_cpus_shutdown(bool crash_kexec)
{
if (panic_print & PANIC_PRINT_ALL_CPU_BT)
if (panic_print & PANIC_PRINT_ALL_CPU_BT) {
/* Temporary allow non-panic CPUs to write their backtraces. */
panic_triggering_all_cpu_backtrace = true;
trigger_all_cpu_backtrace();
panic_triggering_all_cpu_backtrace = false;
}
/*
* Note that smp_send_stop() is the usual SMP shutdown function,

2
kernel/printk/printk.c
View file

@ -2316,7 +2316,7 @@ asmlinkage int vprintk_emit(int facility, int level,
* non-panic CPUs are generating any messages, they will be
* silently dropped.
*/
if (other_cpu_in_panic())
if (other_cpu_in_panic() && !panic_triggering_all_cpu_backtrace)
return 0;
if (level == LOGLEVEL_SCHED) {