[PATCH AUTOSEL 5.16 35/59] printk: use atomic updates for klogd work

Sasha Levin
2022-03-30T11:58:48Z

From: John Ogness <john.ogness@linutronix.de>

[ Upstream commit 2ba3673d70178bf07fb75ff25c54bc478add4021 ]

The per-cpu @printk_pending variable can be updated from
sleepable contexts, such as:

get_random_bytes()
warn_unseeded_randomness()
printk_deferred()
defer_console_output()

and can be updated from interrupt contexts, such as:

handle_irq_event_percpu()
__irq_wake_thread()
wake_up_process()
try_to_wake_up()
select_task_rq()
select_fallback_rq()
printk_deferred()
defer_console_output()

and can be updated from NMI contexts, such as:

vprintk()
if (in_nmi()) defer_console_output()

Therefore the atomic variant of the updating functions must be used.

Replace __this_cpu_xchg() with this_cpu_xchg().
Replace __this_cpu_or() with this_cpu_or().

Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/87iltld4ue.fsf@jogness.linutronix.de
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/printk/printk.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 92eb7785e6e7..9aa27702363c 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3257,7 +3257,7 @@ static DEFINE_PER_CPU(int, printk_pending);

static void wake_up_klogd_work_func(struct irq_work *irq_work)
{
- int pending = __this_cpu_xchg(printk_pending, 0);
+ int pending = this_cpu_xchg(printk_pending, 0);

if (pending & PRINTK_PENDING_OUTPUT) {
/* If trylock fails, someone else is doing the printing */
@@ -3291,7 +3291,7 @@ void defer_console_output(void)
return;

preempt_disable();
- __this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
+ this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
preempt_enable();
}
--
2.34.1