6.10-stable review patch. If anyone has any objections, please let me know.
------------------
From: Ryo Takakura <takakura@xxxxxxxxxxxxx>
[ Upstream commit bcc954c6caba01fca143162d5fbb90e46aa1ad80 ]
commit 779dbc2e78d7 ("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: 779dbc2e78d7 ("printk: Avoid non-panic CPUs writing to ringbuffer")
Signed-off-by: Ryo Takakura <takakura@xxxxxxxxxxxxx>
Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
Link: https://lore.kernel.org/r/20240812072703.339690-1-takakura@xxxxxxxxxxxxx
Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
include/linux/panic.h | 1 +
kernel/panic.c | 8 +++++++-
kernel/printk/printk.c | 2 +-
3 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/include/linux/panic.h b/include/linux/panic.h
index 6717b15e798c3..556b4e2ad9aa5 100644
--- a/include/linux/panic.h
+++ b/include/linux/panic.h
@@ -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;
diff --git a/kernel/panic.c b/kernel/panic.c
index 8bff183d6180e..30342568e935f 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -63,6 +63,8 @@ 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);
@@ -252,8 +254,12 @@ 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,
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index dddb15f48d595..c5d844f727f63 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -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) {
--
2.43.0
