[PATCH AUTOSEL 6.5 2/6] printk: Keep non-panic-CPUs out of console lock

Sasha Levin
2023-09-09T01:13:59Z

[ 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@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230717194607.145135-4-john.ogness@linutronix.de
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/printk/printk.c | 45 ++++++++++++++++++++++++------------------
1 file changed, 26 insertions(+), 19 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 7d3f30eb35862..591c11888200d 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2585,6 +2585,25 @@ 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 - block the console subsystem from printing
*
@@ -2597,6 +2616,10 @@ 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;
@@ -2615,6 +2638,9 @@ 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) {
@@ -2633,25 +2659,6 @@ 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.
--
2.40.1