linux-kernel - [PATCH 1/2] stop_machine: check work->done while handling enqueued works

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Message-ID: <CAJd=RBCi0gRGf2ronNyGDBeNsBJkEZ6aTe29gVnTUD2qh6Bnog@mail.gmail.com>
Date:	Sun, 10 Feb 2013 13:22:43 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Namhyung Kim <namhyung@...nel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Hillf Danton <dhillf@...il.com>
Subject: [PATCH 1/2] stop_machine: check work->done while handling enqueued works

In cpu_stopper_thread(), @work->done may be NULL if the cpu stop work
is queued from stop_one_cpu_nowait(); however, cpu_stopper_thread()
updates @done->ret without checking whether @done exists or not when
the work function fails.

While this can lead to oops, the only current user of
stop_one_cpu_nowait() - active_load_balance_cpu_stop() - always
returns 0 and thus there's no in-kernel user which triggers this bug.

Fix it by checking whether @done exists before updating @done->ret.

Thanks Tejun for sharing commit message.

Signed-off-by: Hillf Danton <dhillf@...il.com>
Reviewed-by: Namhyung Kim <namhyung@...nel.org>
---

--- a/kernel/stop_machine.c	Sun Feb 10 12:51:46 2013
+++ b/kernel/stop_machine.c	Sun Feb 10 12:58:58 2013
@@ -279,7 +279,7 @@ repeat:
 		preempt_disable();

 		ret = fn(arg);
-		if (ret)
+		if (ret && done)
 			done->ret = ret;

 		/* restore preemption and check it's still balanced */
--
--
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