linux-kernel - [PATCH] panic: Reenable preemption in WARN slowpath

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Date:   Wed, 15 Sep 2023 09:55:39 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] panic: Reenable preemption in WARN slowpath

Commit 5a5d7e9badd2 ("cpuidle: lib/bug: Disable rcu_is_watching() during
WARN/BUG") amended warn_slowpath_fmt() to disable preemption until the
WARN splat has been emitted.

However the commit neglected to reenable preemption in the !fmt codepath,
i.e. when a WARN splat is emitted without additional format string.

One consequence is that users may see more splats than intended.  E.g. a
WARN splat emitted in a work item results in at least two extra splats:

  BUG: workqueue leaked lock or atomic
  (emitted by process_one_work())

  BUG: scheduling while atomic
  (emitted by worker_thread() -> schedule())

Ironically the point of the commit was to *avoid* extra splats. ;)

Fix it.

Fixes: 5a5d7e9badd2 ("cpuidle: lib/bug: Disable rcu_is_watching() during WARN/BUG")
Signed-off-by: Lukas Wunner <lukas@...ner.de>
Cc: stable@...r.kernel.org # v6.1+
Cc: Peter Zijlstra <peterz@...radead.org>
---
The original commit went in through the tip tree, hence submitting to
tip maintainers.  The commit was backported to v6.1-stable (even though
it wasn't tagged for stable), hence this fix needs a stable designation.

 kernel/panic.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/panic.c b/kernel/panic.c
index 07239d4..ffa037fa 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -697,6 +697,7 @@ void warn_slowpath_fmt(const char *file, int line, unsigned taint,
 	if (!fmt) {
 		__warn(file, line, __builtin_return_address(0), taint,
 		       NULL, NULL);
+		warn_rcu_exit(rcu);
 		return;
 	}
 
-- 
2.39.2