Date:	Fri, 24 Apr 2009 00:47:01 -0400
From:	Josef 'Jeff' Sipek <jeffpc@...efsipek.net>
To:	Jens Axboe <jens.axboe@...cle.com>, Jeff Moyer <jmoyer@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: CFQ Oops

I got an oops with CFQ (see below) while running the XFS QA test 133. I managed
to bisect it down to commit a36e71f996e25d6213f57951f7ae1874086ec57e.

>From a quick glance at the code, I'd guess that prio_trees[..] happens to be
NULL, and so the rb_erase_init call on line 660 results in a NULL ptr deref.

657             if (!RB_EMPTY_NODE(&cfqq->rb_node))
658                     cfq_rb_erase(&cfqq->rb_node, &cfqd->service_tree);
659             if (!RB_EMPTY_NODE(&cfqq->p_node))
660                     rb_erase_init(&cfqq->p_node, &cfqd->prio_trees[cfqq->ioprio]);
661
662             BUG_ON(!cfqd->busy_queues);
663             cfqd->busy_queues--;

Josef 'Jeff' Sipek.


a36e71f996e25d6213f57951f7ae1874086ec57e is first bad commit
commit a36e71f996e25d6213f57951f7ae1874086ec57e
Author: Jens Axboe <jens.axboe@...cle.com>
Date:   Wed Apr 15 12:15:11 2009 +0200

    cfq-iosched: add close cooperator code

    If we have processes that are working in close proximity to each
    other on disk, we don't want to idle wait. Instead allow the close
    process to issue a request, getting better aggregate bandwidth.
    The anticipatory scheduler has similar checks, noop and deadline do
    not need it since they don't care about process <-> io mappings.

    The code for CFQ is a little more involved though, since we split
    request queues into per-process contexts.

    This fixes a performance problem with eg dump(8), since it uses
    several processes in some silly attempt to speed IO up. Even if
    dump(8) isn't really a valid case (it should be fixed by using
    CLONE_IO), there are other cases where we see close processes
    and where idling ends up hurting performance.

    Credit goes to Jeff Moyer <jmoyer@...hat.com> for writing the
    initial implementation.

    Signed-off-by: Jens Axboe <jens.axboe@...cle.com>

:040000 040000 2e905502bf3c466baae407bcd654fc36d015c83f b4aafd7edc811aed69fa44ddf00a29ece4f32a33 M      block



BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<ffffffff8119a594>] rb_erase+0x174/0x340
PGD f8843067 PUD f8842067 PMD 0
Oops: 0000 [#1] SMP
last sysfs file:
/sys/devices/pci0000:00/0000:00:0b.0/0000:01:03.0/local_cpus
CPU 0
Modules linked in: xfs exportfs sco bridge stp llc bnep l2cap bluetooth
ip6t_REJECT nf_conntrack_ipv6 ip6table_filter ip6_tables ipv6 dm_multipath
uinput amd_rng ata_generic tg3 s2io libphy serio_raw i2c_amd8111 pcspkr
i2c_amd756 pata_amd shpchp
Pid: 2926, comm: xfs_io Not tainted 2.6.30-rc3 #8 To be filled by O.E.M.
RIP: 0010:[<ffffffff8119a594>]  [<ffffffff8119a594>] rb_erase+0x174/0x340
RSP: 0018:ffff8800788e9788  EFLAGS: 00010046
RAX: ffff8800f9dd12b1 RBX: ffff8800f9dd12b0 RCX: 0000000000000001
RDX: ffff8800f9dd12b0 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffff8800788e9798 R08: ffff8800f9dd1320 R09: 0000000000000000
R10: ffff8800f9dd12b0 R11: 0000000000000000 R12: ffff8800fa958a38
R13: ffff880074cc8e60 R14: ffff8800fa958a00 R15: ffff8800f9dd1320
FS:  00007f6262cc46f0(0000) GS:ffffc20000000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000000000000 CR3: 00000000f5848000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process xfs_io (pid: 2926, threadinfo ffff8800788e8000, task
ffff880074d0c4d0)
Stack:
 ffff8800f9dd1320 ffff8800f9dd1350 ffff8800788e97d8 ffffffff81190a40
 ffff8800fa958a00 ffff8800f9dd1320 ffff880074cc8e60 ffff8800fa958a00
 ffff8800fa9208e0 ffff880074cc8e60 ffff8800788e9808 ffffffff81190b28
Call Trace:
 [<ffffffff81190a40>] cfq_remove_request+0x1e0/0x280
 [<ffffffff81190b28>] cfq_dispatch_insert+0x48/0x90
 [<ffffffff811917a5>] cfq_dispatch_requests+0x1a5/0x4d0
 [<ffffffff81180842>] elv_next_request+0x162/0x200
 [<ffffffff81196dba>] ? kobject_get+0x1a/0x30
 [<ffffffff812156d2>] scsi_request_fn+0x62/0x560
 [<ffffffff8138a5ff>] ? _spin_unlock_irqrestore+0x2f/0x40
 [<ffffffff8118251a>] blk_start_queueing+0x1a/0x40
 [<ffffffff81191f15>] cfq_insert_request+0x2d5/0x430
 [<ffffffff81180a00>] elv_insert+0x120/0x2a0
 [<ffffffff81180bfb>] __elv_add_request+0x7b/0xd0
 [<ffffffff81183cf1>] __make_request+0x111/0x460
 [<ffffffff81182bf5>] generic_make_request+0x3b5/0x490
 [<ffffffff81182d40>] submit_bio+0x70/0xf0
 [<ffffffff8110d86e>] dio_bio_submit+0x5e/0x90
 [<ffffffff8110e215>] __blockdev_direct_IO+0x5c5/0xd60
 [<ffffffffa019916e>] xfs_vm_direct_IO+0x10e/0x130 [xfs]
 [<ffffffffa01995a0>] ? xfs_get_blocks_direct+0x0/0x20 [xfs]
 [<ffffffffa01992f0>] ? xfs_end_io_direct+0x0/0x80 [xfs]
 [<ffffffff810a59ef>] generic_file_direct_write+0xbf/0x220
 [<ffffffffa01a19bb>] xfs_write+0x3fb/0x9a0 [xfs]
 [<ffffffff810a4f6c>] ? filemap_fault+0x13c/0x440
 [<ffffffffa019dafd>] xfs_file_aio_write+0x5d/0x70 [xfs]
 [<ffffffff810e16f1>] do_sync_write+0xf1/0x140
 [<ffffffff8105b1d0>] ? autoremove_wake_function+0x0/0x40
 [<ffffffff8103cc7b>] ? finish_task_switch+0x5b/0xe0
 [<ffffffffa0199190>] ? xfs_end_bio_written+0x0/0x30 [xfs]
 [<ffffffff81387ba0>] ? thread_return+0x3e/0x6ae
 [<ffffffff810e1ddb>] vfs_write+0xcb/0x190
 [<ffffffff810e1f32>] sys_pwrite64+0x92/0xa0
 [<ffffffff8100bf6b>] system_call_fastpath+0x16/0x1b
Code: 7a ff ff ff 0f 1f 00 48 3b 78 10 0f 1f 40 00 0f 84 7a 01 00 00 48 89
48 08 66 0f 1f 44 00 00 e9 28 ff ff ff 0f 1f 00 48 8b 7b 08 <48> 8b 07 a8 01
0f 84 d1 00 00 00 48 8b 47 10 48 85 c0 74 09 f6
RIP  [<ffffffff8119a594>] rb_erase+0x174/0x340
 RSP <ffff8800788e9788>
CR2: 0000000000000000
---[ end trace 79edd488f3f3e8df ]---

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