On Sat, 24 Dec 2011, Tejun Heo wrote: > While fixing io_context creation / task exit race condition, > 6e736be7f2 "block: make ioc get/put interface more conventional and > fix race on alloction" also prevented an exiting (%PF_EXITING) task > from creating its own io_context. This is incorrect as exit path may > issue IOs, e.g. from exit_files(), and if those IOs are the first ones > issued by the task, io_context needs to be created to process the IOs. > > Combined with the existing problem of io_context / io_cq creation > failure having the possibility of stalling IO, this problem results in > deterministic full IO lockup with certain workloads. > > Fix it by allowing io_context creation regardless of %PF_EXITING for > %current. > > Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> > Reported-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Reported-by: Hugh Dickins <hughd@xxxxxxxxxx> Thanks, I think I've now built enough kernels on -next plus your patch to say that it does indeed solve that problem. 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 ]--- Hugh -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
