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

From: Hillf Danton
Date: Sun Feb 10 2013 - 00:23:01 EST

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@xxxxxxxxx>
Reviewed-by: Namhyung Kim <namhyung@xxxxxxxxxx>

--- 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:

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

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