[PATCH 2/2] stop_machine: dequeue work before signal completion

From: Hillf Danton
Date: Sun Feb 10 2013 - 00:26:15 EST

When a CPU is finally put down in either CPU_UP_CANCELLED or
CPU_POST_DEAD, cpu_stop_cpu_callback() signals immediate completion on
all cpu_stop_works still queued on the dead CPU; unfortunately, this
code is buggy in that it doesn't remove the canceled work items off
the stopper->works leaving it corrupted, which will trigger BUG_ON()
during CPU_UP_PREPARE if the CPU is brought back online.

This bug isn't easily triggered because CPU_DOWN has to race against
cpu_stop calls and most, if not all, cpu stop users pin target CPUs.

Fix it by popping each work item off stopper->works.

Thanks Tejun for sharing commit message, again.

Signed-off-by: Hillf Danton <dhillf@xxxxxxxxx>
Reviewed-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx

--- a/kernel/stop_machine.c Sun Feb 10 13:00:00 2013
+++ b/kernel/stop_machine.c Sun Feb 10 13:02:18 2013
@@ -334,23 +334,24 @@ static int __cpuinit cpu_stop_cpu_callba
- {
- struct cpu_stop_work *work;
sched_set_stop_task(cpu, NULL);
/* kill the stopper */
/* drain remaining works */
- list_for_each_entry(work, &stopper->works, list)
+ while (!list_empty(&stopper->works)) {
+ struct cpu_stop_work *work;
+ work = list_first_entry(&stopper->works,
+ struct cpu_stop_work, list);
+ list_del_init(&work->list);
cpu_stop_signal_done(work->done, false);
+ }
stopper->enabled = false;
/* release the stopper */
stopper->thread = NULL;
- }

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