If another CPU is in panic, we are about to be halted. Try to gracefully
abandon the console_sem, leaving it free for the panic CPU to grab.
Suggested-by: Petr Mladek <[email protected]>
Signed-off-by: Stephen Brennan <[email protected]>
---
Notes:
v2: Factor check out to a helper, and check at the end of
console_unlock() to prevent retry as well.
kernel/printk/printk.c | 25 ++++++++++++++++++++++++-
1 file changed, 24 insertions(+), 1 deletion(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 736f00d33087..a174c4b2d156 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2598,6 +2598,25 @@ static int have_callable_console(void)
return 0;
}
+/*
+ * Return true when this CPU should unlock console_sem without pushing all
+ * messages to the console. This reduces the chance that the console is
+ * locked when the panic CPU tries to use it.
+ */
+static bool abandon_console_lock_in_panic(void)
+{
+ if (!panic_in_progress())
+ return false;
+
+ /*
+ * We can use raw_smp_processor_id() here because it is impossible for
+ * the task to be migrated to the panic_cpu, or away from it. If
+ * panic_cpu has already been set, and we're not currently executing on
+ * that CPU, then we never will be.
+ */
+ return atomic_read(&panic_cpu) != raw_smp_processor_id();
+}
+
/*
* Can we actually use the console at this time on this cpu?
*
@@ -2746,6 +2765,10 @@ void console_unlock(void)
if (handover)
return;
+ /* Allow panic_cpu to take over the consoles safely */
+ if (abandon_console_lock_in_panic())
+ break;
+
if (do_cond_resched)
cond_resched();
}
@@ -2763,7 +2786,7 @@ void console_unlock(void)
* flush, no worries.
*/
retry = prb_read_valid(prb, next_seq, NULL);
- if (retry && console_trylock())
+ if (retry && !abandon_console_lock_in_panic() && console_trylock())
goto again;
}
EXPORT_SYMBOL(console_unlock);
--
2.30.2