We encountered following panic several times: [ 74.671982] BUG: unable to handle kernel NULL pointer dereference at 00000008 [ 74.672101] IP: [<c129bb27>] wake_futex+0x47/0x80 [ 74.672185] *pdpt = 0000000010108001 *pde = 0000000000000000 [ 74.672278] Oops: 0002 [#1] PREEMPT SMP [ 74.672403] Modules linked in: atomisp_css2400b0_v2 atomisp_css2400_v2 dfrgx bcm_bt_lpm videobuf_vmalloc videobuf_core hdmi_audio tngdisp bcm4335 kct_daemon(O) cfg80211 [ 74.672815] CPU: 0 PID: 1477 Comm: zygote Tainted: G W O 3.10.1-259934-g0bfb86e #1 [ 74.672855] Hardware name: Intel Corporation Merrifield/SALT BAY, BIOS 404 2013.10.09:15.29.48 [ 74.672894] task: d4c97220 ti: cfaa8000 task.ti: cfaa8000 [ 74.672933] EIP: 0060:[<c129bb27>] EFLAGS: 00210246 CPU: 0 [ 74.672975] EIP is at wake_futex+0x47/0x80 [ 74.673012] EAX: 00000000 EBX: 00000000 ECX: 00000000 EDX: 00000000 [ 74.673049] ESI: def4de5c EDI: ffffffff EBP: cfaa9eb4 ESP: cfaa9ea0 [ 74.673086] DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068 [ 74.673123] CR0: 8005003b CR2: 00000008 CR3: 10109000 CR4: 001007f0 [ 74.673160] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000 [ 74.673196] DR6: ffff0ff0 DR7: 00000400 [ 74.673229] Stack: [ 74.673260] 00000000 00000001 00000000 def4de5c c225eb50 cfaa9ee4 c129bc29 00000000 [ 74.673536] 00000000 7fffffff c225eb30 b4f38000 ec1a4b40 00000f90 7fffffff 00000001 [ 74.673814] b4f38f90 cfaa9f58 c129da0b ffffffff ffffffff cfaa9f10 c195d835 00000001 [ 74.674092] Call Trace: [ 74.674144] [<c129bc29>] futex_wake+0xc9/0x110 [ 74.674195] [<c129da0b>] do_futex+0xeb/0x950 [ 74.674246] [<c195d835>] ? sub_preempt_count+0x55/0xe0 [ 74.674293] [<c1275aee>] ? wake_up_new_task+0xee/0x190 [ 74.674341] [<c195a31b>] ? _raw_spin_unlock_irqrestore+0x3b/0x70 [ 74.674388] [<c1275aee>] ? wake_up_new_task+0xee/0x190 [ 74.674436] [<c1241afc>] ? do_fork+0xec/0x350 [ 74.674484] [<c129e30b>] SyS_futex+0x9b/0x140 [ 74.674533] [<c1312298>] ? SyS_mprotect+0x188/0x1e0 [ 74.674582] [<c195a718>] syscall_call+0x7/0xb On smp systems, setting current task to q->task in queue_me() may not visible immediately to another cpu, some times this will cause panic in wake_futex(). Adding memory barrier to avoid this. Signed-off-by: Leon Ma <xindong.ma@xxxxxxxxx> Signed-off-by: xiaobing tu <xiaobing.tu@xxxxxxxxx> --- kernel/futex.c | 1 + 1 files changed, 1 insertions(+), 0 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index 80ba086..792cd41 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1529,6 +1529,7 @@ static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb) plist_node_init(&q->list, prio); plist_add(&q->list, &hb->chain); q->task = current; + smp_mb(); spin_unlock(&hb->lock); } -- 1.7.4.1 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html