From 283743680eb1b71325b0f14deca93b465d4b9328 Mon Sep 17 00:00:00 2001 From: Subbaraman Narayanamurthy Date: Fri, 20 Jun 2014 12:45:54 -0700 Subject: [PATCH] kthread: Fix the race condition when kthread is parked 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 : [] lr : [] 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 the parked completion. CRs-Fixed: 659674 Change-Id: If3f0e9b706eeb5d30d5a32f84378d35bb03fe794 Signed-off-by: Subbaraman Narayanamurthy --- kernel/kthread.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/kthread.c b/kernel/kthread.c index 760e86df8c20..c56c6f8ec607 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;