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Date: Thu, 14 Jun 2012 18:01:29 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Andrey Vagin <avagin@openvz.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Cyrill Gorcunov <gorcunov@openvz.org>,
        Pavel Emelyanov <xemul@openvz.org>
Subject: Re: general protection fault on finalizing task
Message-ID: <20120614160129.GA3433@redhat.com>
References: <CANaxB-xyBw+O9h7OrFRNM93+Gp+GX63C-OgOZ2ZK2QbKMDBJ7g@mail.gmail.com>
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Hi Andrey,

On 06/14, Andrey Vagin wrote:
>
> Hello,
>
> I'm developing CRIU (criu.org) and got this GP. I have seen it a few
> time with the same stack trace.
> It's not reproduced on 3.4.0-rc4+.
>
> general protection fault: 0000 [#1] SMP
> CPU 0
> Modules linked in: udp_diag bridge stp llc ipv6 ext4 jbd2 dm_mirror
> dm_region_hash dm_log dm_mod pcspkr virtio_balloon 8139too 8139cp mii
> i2c_piix4 i2c_core ext3 jbd mbcache virtio_blk virtio_pci virtio_ring
> virtio pata_acpi ata_generic ata_piix floppy [last unloaded:
> scsi_wait_scan]
>
> Pid: 1647, comm: crtools Not tainted 3.5.0-rc2+ #203 Red Hat KVM
> RIP: 0010:[<ffffffff811b453a>]  [<ffffffff811b453a>] d_hash_and_lookup+0x2a/0x70

Could you please re-test with these

	http://marc.info/?l=linux-mm-commits&m=133962463616232
	http://marc.info/?l=linux-mm-commits&m=133962463616231

patches applied?


> RSP: 0018:ffff88001651bd28  EFLAGS: 00010246
> RAX: 0000000000003531 RBX: ffff88001651bd68 RCX: 0000000000000010
> RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000003531
> RBP: ffff88001651bd38 R08: 000000000000fffa R09: 0000000000000002
> R10: 0000000000000000 R11: 000000000000fffd R12: 6b6b6b6b6b6b6b6b
> R13: ffff88001a3b3db0 R14: ffff88001651bd68 R15: 000000000000000f
> FS:  00007ff80c4a2700(0000) GS:ffff88001f800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> CR2: 00007ff80c4ac000 CR3: 0000000001a0b000 CR4: 00000000000006f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Process crtools (pid: 1647, threadinfo ffff88001651a000, task ffff880017154c40)
> Stack:
>  ffff88001651bd78 0000000000000001 ffff88001651bdc8 ffffffff812050c0
>  ffff8800185b44b0 ffff88001721e4a0 ffff88001721e4a0 0000000f81057b6c
>  0000000200003531 ffff88001651bd78 ffff880032003531 0000000000000246
> Call Trace:
>  [<ffffffff812050c0>] proc_flush_task+0xa0/0x1e0
>  [<ffffffff81057c0e>] release_task+0xce/0x690
>  [<ffffffff81057b6c>] ? release_task+0x2c/0x690
>  [<ffffffff810622c2>] exit_ptrace+0x102/0x140
>  [<ffffffff81059c64>] do_exit+0x214/0xa70
>  [<ffffffff81553cbb>] ? _raw_read_unlock+0x2b/0x50
>  [<ffffffff8105a51b>] do_group_exit+0x5b/0xd0
>  [<ffffffff8105a5a7>] sys_exit_group+0x17/0x20
>  [<ffffffff8155cee9>] system_call_fastpath+0x16/0x1b
> Code: 00 55 48 89 e5 48 83 ec 10 48 89 1c 24 4c 89 64 24 08 66 66 66
> 66 90 48 89 f3 49 89 fc 8b 76 04 48 8b 7b 08 e8 58 0c ff ff 89 03 <41>
> f6 04 24 01 75 1f 48 89 de 4c 89 e7 e8 64 ff ff ff 48 8b 1c
> RIP  [<ffffffff811b453a>] d_hash_and_lookup+0x2a/0x70
>  RSP <ffff88001651bd28>
> ---[ end trace 250bb1fa95f4b805 ]---
> Fixing recursive fault but reboot is needed!
>
> Steps to reproduce:
> * # git clone git://github.com/avagin/crtools.git -b gp-3.5
> * # cd crtools
> * # make && make -C test
> * # while :; do bash test/zdtm.sh pidns/static/session00 || break; done
> * Wait a few seconds
>
> session00 is a test case for checking, that session ids restored correctly.
> it create about 10 processes in a separate pidns, some of them wait
> children, other ones
> wait on read from pipe. crtools freezes and dumps state of this
> processes and kill processes.
>
> The bug is reproduced, when crtools try to kill tasks (in this moment
> crtools attached to this tasks by ptrace).
> The meta code looks like:
> for_each_task(pid) {
>   kill(pid, SIGKILL);
>   ptrace(PTRACE_DETACH, pid, NULL, NULL);
> }

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