linux-kernel - [tip: core/urgent] panic: Reenable preemption in WARN slowpath

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Date:   Fri, 15 Sep 2023 09:36:23 -0000
From:   "tip-bot2 for Lukas Wunner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Lukas Wunner <lukas@...ner.de>, Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: core/urgent] panic: Reenable preemption in WARN slowpath

The following commit has been merged into the core/urgent branch of tip:

Commit-ID:     cccd32816506cbac3a4c65d9dff51b3125ef1a03
Gitweb:        https://git.kernel.org/tip/cccd32816506cbac3a4c65d9dff51b3125ef1a03
Author:        Lukas Wunner <lukas@...ner.de>
AuthorDate:    Fri, 15 Sep 2023 09:55:39 +02:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Fri, 15 Sep 2023 11:28:08 +02:00

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>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Paul E. McKenney <paulmck@...nel.org>
Link: https://lore.kernel.org/r/3ec48fde01e4ee6505f77908ba351bad200ae3d1.1694763684.git.lukas@wunner.de
---
 kernel/panic.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/panic.c b/kernel/panic.c
index 07239d4..ffa037f 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;
 	}