[PATCH] kthread: Fix the race condition when kthread is parked
From: Subbaraman Narayanamurthy
Date: Wed Jun 25 2014 - 15:43:25 EST
While stressing the CPU hotplug path, sometimes we hit a problem
as shown below.
[57056.416774] ------------[ cut here ]------------
[57056.489232] ksoftirqd/1 (14): undefined instruction: pc=c01931e8
[57056.489245] Code: e594a000 eb085236 e15a0000 0a000000 (e7f001f2)
[57056.489259] ------------[ cut here ]------------
[57056.492840] kernel BUG at kernel/kernel/smpboot.c:134!
[57056.513236] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
[57056.519055] Modules linked in: wlan(O) mhi(O)
[57056.523394] CPU: 0 PID: 14 Comm: ksoftirqd/1 Tainted: G W O
3.10.0-g3677c61-00008-g180c060 #1
[57056.532595] task: f0c8b000 ti: f0e78000 task.ti: f0e78000
[57056.537991] PC is at smpboot_thread_fn+0x124/0x218
[57056.542750] LR is at smpboot_thread_fn+0x11c/0x218
[57056.547528] pc : [<c01931e8>] lr : [<c01931e0>] psr: 200f0013
[57056.547528] sp : f0e79f30 ip : 00000000 fp : 00000000
[57056.558983] r10: 00000001 r9 : 00000000 r8 : f0e78000
[57056.564192] r7 : 00000001 r6 : c1195758 r5 : f0e78000 r4 : f0e5fd00
[57056.570701] r3 : 00000001 r2 : f0e79f20 r1 : 00000000 r0 : 00000000
This issue was always seen in the context of "ksoftirqd". It seems to
be happening because of a potential race condition in __kthread_parkme
where just after completing the parked completion, before the
ksoftirqd task has been scheduled again, it can go into running state.
Fix this by waiting for the task state to parked after waiting for the
parked completion.
Signed-off-by: Subbaraman Narayanamurthy <subbaram@xxxxxxxxxxxxxx>
---
kernel/kthread.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 760e86d..c56c6f8 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -398,6 +398,8 @@ int kthread_park(struct task_struct *k)
if (k != current) {
wake_up_process(k);
wait_for_completion(&kthread->parked);
+ while (k->state != TASK_PARKED)
+ cond_resched();
}
}
ret = 0;
--
1.8.2.1
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