On 11/20/2012 03:10 PM, Darren Hart wrote: > > > On 11/20/2012 08:46 AM, Dave Jones wrote: >> On Wed, Oct 24, 2012 at 09:44:07PM -0700, Darren Hart wrote: >> >> > > I've been able to trigger this for the last week or so. >> > > Unclear whether this is a new bug, or my fuzzer got smarter, but I see >> the >> > > pi-futex code hasn't changed since the last time it found something.. >> > > >> > > > BUG: unable to handle kernel NULL pointer dereference at >> 0000000000000018 >> > > > IP: [<ffffffff810e185e>] __lock_acquire+0x5e/0x1ba0 >> > > > PGD 8e72c067 PUD 34f07067 PMD 0 >> > > > Oops: 0000 [#1] PREEMPT SMP >> > > > CPU 7 >> > > > Pid: 27513, comm: trinity-child0 Not tainted 3.7.0-rc2+ #43 >> > > > RIP: 0010:[<ffffffff810e185e>] [<ffffffff810e185e>] >> __lock_acquire+0x5e/0x1ba0 >> > > > RSP: 0018:ffff8800803f7b28 EFLAGS: 00010046 >> > > > RAX: 0000000000000086 RBX: 0000000000000000 RCX: 0000000000000000 >> > > > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000018 >> > > > RBP: ffff8800803f7c18 R08: 0000000000000002 R09: 0000000000000000 >> > > > R10: 0000000000000000 R11: 2222222222222222 R12: 0000000000000002 >> > > > R13: ffff880051dd8000 R14: 0000000000000002 R15: 0000000000000018 >> > > > FS: 00007f9fc6ccb740(0000) GS:ffff880148a00000(0000) >> knlGS:0000000000000000 >> > > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> > > > CR2: 0000000000000018 CR3: 000000008e6fb000 CR4: 00000000001407e0 >> > > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >> > > > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 >> > > > Process trinity-child0 (pid: 27513, threadinfo ffff8800803f6000, >> task ffff880051dd8000) >> > > > Stack: >> > > > ffff8800803f7b48 ffffffff816c5c59 ffff8800803f7b48 ffff88014840ebc0 >> > > > ffff8800803f7b68 ffffffff816c18e3 ffff8800803f7d10 0000000000000001 >> > > > ffff8800803f7ba8 ffffffff810a1e62 ffff8800803f7d10 0000000000000282 >> > > > Call Trace: >> > > > [<ffffffff816c5c59>] ? sub_preempt_count+0x79/0xd0 >> > > > [<ffffffff816c18e3>] ? _raw_spin_unlock_irqrestore+0x73/0xa0 >> > > > [<ffffffff810a1e62>] ? hrtimer_try_to_cancel+0x52/0x210 >> > > > [<ffffffff810eb9e5>] ? debug_rt_mutex_free_waiter+0x15/0x180 >> > > > [<ffffffff816c0107>] ? rt_mutex_slowlock+0x127/0x1b0 >> > > > [<ffffffff810b7039>] ? local_clock+0x89/0xa0 >> > > > [<ffffffff810e3ac2>] lock_acquire+0xa2/0x220 >> > > > [<ffffffff810e812c>] ? futex_lock_pi.isra.18+0x1cc/0x390 >> > > > [<ffffffff816c09e0>] _raw_spin_lock+0x40/0x80 >> > > > [<ffffffff810e812c>] ? futex_lock_pi.isra.18+0x1cc/0x390 >> > > > [<ffffffff810e812c>] futex_lock_pi.isra.18+0x1cc/0x390 >> > > > [<ffffffff810a1980>] ? update_rmtp+0x70/0x70 >> > > > [<ffffffff810e99e4>] do_futex+0x394/0xa50 >> > > > [<ffffffff8119ec43>] ? might_fault+0x53/0xb0 >> > > > [<ffffffff810ea12d>] sys_futex+0x8d/0x190 >> > > > [<ffffffff816ca288>] tracesys+0xe1/0xe6 >> > > > Code: d8 45 0f 45 e0 4c 89 75 f0 4c 89 7d f8 85 c0 0f 84 f8 00 00 00 >> 8b 05 22 fe f3 00 49 89 ff 89 f3 41 89 d2 85 c0 0f 84 02 01 00 00 <49> 8b 07 >> ba 01 00 00 00 48 3d c0 81 06 82 44 0f 44 e2 83 fb 01 >> > > > RIP [<ffffffff810e185e>] __lock_acquire+0x5e/0x1ba0 >> > > > RSP <ffff8800803f7b28> >> > > > CR2: 0000000000000018 >> > > >> > > It looks like we got all the way to lock_acquire with a NULL 'lock' >> somehow. >> > > >> > > Darren, any idea how this could happen ? >> > >> > I'm digging. Can you get trinity to provide the arguments it used that >> > trigger the crash?u That might help hone in on the exact path. >> >> Still seeing this on rc6. It happens very quickly when I run with "-c futex" >> I just pushed out all the pending trinity changes I was running with, but >> I don't think they would have been responsible. >> >> Dave >> > > OK, so some instrumentation yields: > > [ 1320.762028] futex_lock_pi: timed lock > [ 1320.762488] futex_lock_pi: hb=ffffffff81e89e28, > hb->lock=ffffffff81e89e28, &q=ffff880181fa5cd8, q.lock_ptr=ffffffff81e89e28 > [ 1320.763647] q.lock_ptr=ffffffff81e89e28 > [ 1320.764132] fixup_owner: uaddr=00007f05465ac000, q=ffff880181fa5cd8, > locked=0 > [ 1323.066371] futex_lock_pi: hb=ffffffff81e89e28, > hb->lock=ffffffff81e89e28, &q=ffff880181fc5cd8, q.lock_ptr= (null) > [ 1323.069032] ------------[ cut here ]------------ > [ 1323.069817] kernel BUG at kernel/futex.c:2052! > > So somewhere between blocking on the lock and waking, q.lock_ptr is > getting set to NULL. The only legitimate place this happens in is > wake_futex, and I see some wake_futex calls after the futex_lock_pi > calls with the same uaddr in the trinity log. We are supposed to be > protected by the q lock_ptr here and wake_futex aborts any wakes of q's > with a pi_state or rt_waiter.... but .... there appears to be a window > in there. I say a window because I see a similar failure where the > instrumentation doesn't catch the lock_ptr as NULL and fails at a later > point on the same lock. Nice nasty parallel locking race. Digging in. >
OK, the problem is a futex_wake_op() calling wake_futex() without checking for a pi_state or rt_waiters. I'm looking at the best way to fix it, considering moving the check out of futex_wake and into wake_futex... some more analysis needed for the best fix, but will have one by tomorrow. -- Darren Hart Intel Open Source Technology Center Yocto Project - Technical Lead - Linux Kernel -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
