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SubjectRe: [PATCH block/for-3.3/core] block: an exiting task should be allowed to create io_context
Hello, Hugh.

On Wed, Dec 28, 2011 at 12:33:01AM -0800, Hugh Dickins wrote:
> Thanks, I think I've now built enough kernels on -next plus your patch
> to say that it does indeed solve that problem.

Awesome, thanks for verifying the fix.

> However, there are a couple of other unhealthy symptoms I've noticed
> under load in -next's block/cfq layer, both with and without your patch.
>
> One is kernel BUG at block/cfq-iosched.c:2585!
> BUG_ON(RB_EMPTY_ROOT(&cfqq->sort_list));
>
> cfq_dispatch_request+0x1a
> cfq_dispatch_requests+0x5c
> blk_peek_request+0x195
> scsi_request_fn+0x6a
> __blk_run_queue+0x16
> scsi_run_queue+0x18a
> scsi_next_command+0x36
> scsi_io_completion+0x426
> scsi_finish_command+0xaf
> scsi_softirq_done+0xdd
> blk_done_softirq+0x6c
> __do_softirq+0x80
> call_softirq+0x1c
> do_softirq+0x33
> irq_exit+0x3f
> do_IRQ+0x97
> ret_from_intr
>
> I've had that one four times now on different machines; but quicker
> to reproduce are these warnings from CONFIG_DEBUG_LIST=y:
>
> ------------[ cut here ]------------
> WARNING: at lib/list_debug.c:53 __list_del_entry+0x8d/0x98()
> Hardware name: 4174AY9
> list_del corruption. prev->next should be ffff880005aa1380, but was 6b6b6b6b6b6b6b6b
> Modules linked in: snd_pcm_oss snd_mixer_oss snd_seq snd_seq_device
> Pid: 29241, comm: cc1 Tainted: G W 3.2.0-rc6-next-20111222 #18
> Call Trace:
> <IRQ> [<ffffffff810544b4>] warn_slowpath_common+0x80/0x98
> [<ffffffff81054560>] warn_slowpath_fmt+0x41/0x43
> [<ffffffff811fc1a1>] __list_del_entry+0x8d/0x98
> [<ffffffff811df8ab>] cfq_remove_request+0x3b/0xdf
> [<ffffffff811df989>] cfq_dispatch_insert+0x3a/0x87
> [<ffffffff811dfb3b>] cfq_dispatch_request+0x65/0x92
> [<ffffffff811dfbc4>] cfq_dispatch_requests+0x5c/0x133
> [<ffffffff812e103e>] ? scsi_request_fn+0x3b6/0x3d3
> [<ffffffff811d3069>] blk_peek_request+0x195/0x1a6
> [<ffffffff812e103e>] ? scsi_request_fn+0x3b6/0x3d3
> [<ffffffff812e0cf5>] scsi_request_fn+0x6d/0x3d3
> [<ffffffff811d0730>] __blk_run_queue+0x19/0x1b
> [<ffffffff811d0bfd>] blk_run_queue+0x21/0x35
> [<ffffffff812e08c4>] scsi_run_queue+0x11f/0x1b9
> [<ffffffff812e205c>] scsi_next_command+0x36/0x46
> [<ffffffff812e24dc>] scsi_io_completion+0x426/0x4a9
> [<ffffffff812dc0b2>] scsi_finish_command+0xaf/0xb8
> [<ffffffff812e200c>] scsi_softirq_done+0xdd/0xe5
> [<ffffffff811d79c6>] blk_done_softirq+0x76/0x8a
> [<ffffffff8105a28d>] __do_softirq+0x98/0x136
> [<ffffffff814e649c>] call_softirq+0x1c/0x30
> [<ffffffff8102f187>] do_softirq+0x38/0x81
> [<ffffffff8105a596>] irq_exit+0x4e/0xb6
> [<ffffffff8102ee9e>] do_IRQ+0x97/0xae
> [<ffffffff814e49f0>] common_interrupt+0x70/0x70
> <EOI> [<ffffffff814e4a8e>] ? retint_swapgs+0xe/0x13
> ---[ end trace 61fdaa1b260613d1 ]---

Hmm... that looks like cfqq being freed before unlinked. I'll try to
reproduce it. Is there any particular workload you were running?

Thanks.

--
tejun


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