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

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@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>

diff --git a/include/linux/panic.h b/include/linux/panic.h
index 3130e0b5116b0367c00ca940cb9aa95e0e95de0d..54d90b6c5f47bd6978654b3f61261943a37e2052 100644 (file)
--- 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 f861bedc1925e748e6589b0196388784ceba302d..2a0449144f82ea8c3daef723b56f63a22e128657 100644 (file)
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -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,

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 054c0e7784fdfdcb1b3f11a67ccd82289eec810a..c22b07049c382c2174416adfd3aab9afab5a85a9 100644 (file)
--- 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) {