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Message-ID: <87zfrzvhsp.fsf@jogness.linutronix.de>
Date: Wed, 05 Jun 2024 11:57:34 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Petr Mladek <pmladek@...e.com>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>,
Steven Rostedt <rostedt@...dmis.org>,
Juri Lelli <juri.lelli@...hat.com>,
linux-kernel@...r.kernel.org
Subject: [PATCH linux-next] printk: nbcon: Fix nbcon_cpu_emergency_flush()
when preemptible
nbcon_cpu_emergency_flush() can be called in a preemptible
context. In that case the CPU is not in an emergency state.
However, in order to see that the CPU is not in an emergency
state (accessing the per-cpu variable), preemption must be
disabled.
Disable preemption when checking the CPU state.
Reported-by: Juri Lelli <juri.lelli@...hat.com>
Closes: https://lore.kernel.org/aqkcpca4vgadxc3yzcu74xwq3grslj5m43f3eb5fcs23yo2gy4@gcsnqcts5tos
Fixes: 46a1379208b7 ("printk: nbcon: Implement emergency sections")
Signed-off-by: John Ogness <john.ogness@...utronix.de>
---
kernel/printk/nbcon.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index 19f0db6945e4..39eb369880d9 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -1443,8 +1443,19 @@ void nbcon_cpu_emergency_exit(void)
*/
void nbcon_cpu_emergency_flush(void)
{
+ bool is_emergency;
+
+ /*
+ * If this context is not an emergency context, preemption might be
+ * enabled. To be sure, disable preemption when checking if this is
+ * an emergency context.
+ */
+ preempt_disable();
+ is_emergency = (*nbcon_get_cpu_emergency_nesting() != 0);
+ preempt_enable();
+
/* The explicit flush is needed only in the emergency context. */
- if (*(nbcon_get_cpu_emergency_nesting()) == 0)
+ if (!is_emergency)
return;
nbcon_atomic_flush_pending();
--
2.30.2
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