This is a note to let you know that I've just added the patch titled
printk: Keep non-panic-CPUs out of console lock
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
printk-keep-non-panic-cpus-out-of-console-lock.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit bf2b06a8d40d573e7b6d08c86ce8635b9e2554c5
Author: John Ogness <john.ogness@xxxxxxxxxxxxx>
Date: Mon Jul 17 21:52:03 2023 +0206
printk: Keep non-panic-CPUs out of console lock
[ Upstream commit 51a1d258e50e03a0216bf42b6af9ff34ec402ac1 ]
When in a panic situation, non-panic CPUs should avoid holding the
console lock so as not to contend with the panic CPU. This is already
implemented with abandon_console_lock_in_panic(), which is checked
after each printed line. However, non-panic CPUs should also avoid
trying to acquire the console lock during a panic.
Modify console_trylock() to fail and console_lock() to block() when
called from a non-panic CPU during a panic.
Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
Reviewed-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
Link: https://lore.kernel.org/r/20230717194607.145135-4-john.ogness@xxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index e4f1e7478b521..4b9429f3fd6d8 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2552,6 +2552,25 @@ static int console_cpu_notify(unsigned int cpu)
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();
+}
+
/**
* console_lock - lock the console system for exclusive use.
*
@@ -2564,6 +2583,10 @@ void console_lock(void)
{
might_sleep();
+ /* On panic, the console_lock must be left to the panic cpu. */
+ while (abandon_console_lock_in_panic())
+ msleep(1000);
+
down_console_sem();
if (console_suspended)
return;
@@ -2582,6 +2605,9 @@ EXPORT_SYMBOL(console_lock);
*/
int console_trylock(void)
{
+ /* On panic, the console_lock must be left to the panic cpu. */
+ if (abandon_console_lock_in_panic())
+ return 0;
if (down_trylock_console_sem())
return 0;
if (console_suspended) {
@@ -2600,25 +2626,6 @@ int is_console_locked(void)
}
EXPORT_SYMBOL(is_console_locked);
-/*
- * 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();
-}
-
/*
* Check if the given console is currently capable and allowed to print
* records.
