Messages in this thread | | | Date | Thu, 12 Feb 2015 18:28:05 +0100 | From | Oleg Nesterov <> | Subject | Re: BUG: spinlock bad magic on CPU#0, migration/0/9 |
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On 02/11, Davidlohr Bueso wrote: > > On Wed, 2015-02-11 at 16:34 -0800, Paul E. McKenney wrote: > > Hello! > > > > Did an earlier-than-usual port of v3.21 patches to post-v3.19, and > > hit the following on x86_64. This happened after about 15 minutes of > > rcutorture. In contrast, I have been doing successful 15-hour runs > > on v3.19. I will check reproducibility and try to narrow it down. > > Might this be a duplicate of the bug that Raghavendra posted a fix for? > > > > Anyway, this was on 3e8c04eb1174 (Merge branch 'for-3.20' of > > git://git.kernel.org/pub/scm/linux/kernel/git/tj/libata). > > > > [ 837.287011] BUG: spinlock bad magic on CPU#0, migration/0/9 > > [ 837.287013] lock: 0xffff88001ea0fe80, .magic: ffffffff, .owner: gî<81>ÿÿÿÿ/0, .owner_cpu: -42 > > [ 837.287013] CPU: 0 PID: 9 Comm: migration/0 Not tainted 3.19.0+ #1 > > [ 837.287013] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 > > [ 837.287013] ffff88001ea0fe80 ffff88001ea0bc78 ffffffff818f6f4b ffffffff810a5a51 > > [ 837.287013] ffffffff81e500e0 ffff88001ea0bc98 ffffffff818f3755 ffff88001ea0fe80 > > [ 837.287013] ffffffff81ca4396 ffff88001ea0bcb8 ffffffff818f377b ffff88001ea0fe80 > > [ 837.287013] Call Trace: > > [ 837.287013] [<ffffffff818f6f4b>] dump_stack+0x45/0x57 > > [ 837.287013] [<ffffffff810a5a51>] ? console_unlock+0x1f1/0x4c0 > > [ 837.287013] [<ffffffff818f3755>] spin_dump+0x8b/0x90 > > [ 837.287013] [<ffffffff818f377b>] spin_bug+0x21/0x26 > > [ 837.287013] [<ffffffff8109923c>] do_raw_spin_unlock+0x5c/0xa0 > > [ 837.287013] [<ffffffff81902587>] _raw_spin_unlock_irqrestore+0x27/0x50 > > [ 837.287013] [<ffffffff8108f0a1>] complete+0x41/0x50 > > We did have some recent changes in completions: > > 7c34e318 (sched/completion: Add lock-free checking of the blocking case) > de30ec47 (sched/completion: Remove unnecessary ->wait.lock serialization when reading completion state) > > The second one being more related (although both appear to make sense). > Perhaps some subtle implication in the completion_done side that > disappeared with the spinlock?
At first glance both changes look suspicious. Unless at least document how you can use these helpers.
Consider this code:
void xxx(void) { struct completion c;
init_completion(&c);
expose_this_completion(&c);
while (!completion_done(&c) schedule_timeout_uninterruptible(1); }
Before that change this code was correct, now it is not. Hmm and note that this is what stop_machine_from_inactive_cpu() does although I do not know if this is related or not.
Because completion_done() can now race with complete(), the final spin_unlock() can write to the memory after it was freed/reused. In this case it can write to the stack after return.
Add CC's.
Oleg.
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