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Message-ID: <a81cdd5b-d6ad-2a4f-0f6d-40e9db6233cd@huaweicloud.com>
Date: Wed, 17 Jul 2024 11:53:27 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: YangYang <yang.yang@...o.com>, Yu Kuai <yukuai1@...weicloud.com>
Cc: Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
linux-kernel@...r.kernel.org, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH] block: fix deadlock between sd_remove & sd_release
Hi,
在 2024/07/16 17:30, YangYang 写道:
> On 2024/7/16 17:15, Yu Kuai wrote:
>> Hi,
>>
>> 在 2024/07/16 16:38, Yang Yang 写道:
>>> Our test report the following hung task:
>>>
>>> [ 2538.459400] INFO: task "kworker/0:0":7 blocked for more than 188
>>> seconds.
>>> [ 2538.459427] Call trace:
>>> [ 2538.459430] __switch_to+0x174/0x338
>>> [ 2538.459436] __schedule+0x628/0x9c4
>>> [ 2538.459442] schedule+0x7c/0xe8
>>> [ 2538.459447] schedule_preempt_disabled+0x24/0x40
>>> [ 2538.459453] __mutex_lock+0x3ec/0xf04
>>> [ 2538.459456] __mutex_lock_slowpath+0x14/0x24
>>> [ 2538.459459] mutex_lock+0x30/0xd8
>>> [ 2538.459462] del_gendisk+0xdc/0x350
>>> [ 2538.459466] sd_remove+0x30/0x60
>>> [ 2538.459470] device_release_driver_internal+0x1c4/0x2c4
>>> [ 2538.459474] device_release_driver+0x18/0x28
>>> [ 2538.459478] bus_remove_device+0x15c/0x174
>>> [ 2538.459483] device_del+0x1d0/0x358
>>> [ 2538.459488] __scsi_remove_device+0xa8/0x198
>>> [ 2538.459493] scsi_forget_host+0x50/0x70
>>> [ 2538.459497] scsi_remove_host+0x80/0x180
>>> [ 2538.459502] usb_stor_disconnect+0x68/0xf4
>>> [ 2538.459506] usb_unbind_interface+0xd4/0x280
>>> [ 2538.459510] device_release_driver_internal+0x1c4/0x2c4
>>> [ 2538.459514] device_release_driver+0x18/0x28
>>> [ 2538.459518] bus_remove_device+0x15c/0x174
>>> [ 2538.459523] device_del+0x1d0/0x358
>>> [ 2538.459528] usb_disable_device+0x84/0x194
>>> [ 2538.459532] usb_disconnect+0xec/0x300
>>> [ 2538.459537] hub_event+0xb80/0x1870
>>> [ 2538.459541] process_scheduled_works+0x248/0x4dc
>>> [ 2538.459545] worker_thread+0x244/0x334
>>> [ 2538.459549] kthread+0x114/0x1bc
>>>
>>> [ 2538.461001] INFO: task "fsck.":15415 blocked for more than 188
>>> seconds.
>>> [ 2538.461014] Call trace:
>>> [ 2538.461016] __switch_to+0x174/0x338
>>> [ 2538.461021] __schedule+0x628/0x9c4
>>> [ 2538.461025] schedule+0x7c/0xe8
>>> [ 2538.461030] blk_queue_enter+0xc4/0x160
>>> [ 2538.461034] blk_mq_alloc_request+0x120/0x1d4
>>> [ 2538.461037] scsi_execute_cmd+0x7c/0x23c
>>> [ 2538.461040] ioctl_internal_command+0x5c/0x164
>>> [ 2538.461046] scsi_set_medium_removal+0x5c/0xb0
>>> [ 2538.461051] sd_release+0x50/0x94
>>> [ 2538.461054] blkdev_put+0x190/0x28c
>>> [ 2538.461058] blkdev_release+0x28/0x40
>>> [ 2538.461063] __fput+0xf8/0x2a8
>>> [ 2538.461066] __fput_sync+0x28/0x5c
>>> [ 2538.461070] __arm64_sys_close+0x84/0xe8
>>> [ 2538.461073] invoke_syscall+0x58/0x114
>>> [ 2538.461078] el0_svc_common+0xac/0xe0
>>> [ 2538.461082] do_el0_svc+0x1c/0x28
>>> [ 2538.461087] el0_svc+0x38/0x68
>>> [ 2538.461090] el0t_64_sync_handler+0x68/0xbc
>>> [ 2538.461093] el0t_64_sync+0x1a8/0x1ac
>>>
>>> T1: T2:
>>> sd_remove
>>> del_gendisk
>>> __blk_mark_disk_dead
>>> blk_freeze_queue_start
>>> ++q->mq_freeze_depth
>>> bdev_release
>>> mutex_lock(&disk->open_mutex)
>>> sd_release
>>> scsi_execute_cmd
>>> blk_queue_enter
>>> wait_event(!q->mq_freeze_depth)
>>
>> This looks wrong, there is a condition blk_queue_dying() in
>> blk_queue_enter().
>
> 584 static void __blk_mark_disk_dead(struct gendisk *disk)
> 585 {
> ......
> 591
> 592 if (test_bit(GD_OWNS_QUEUE, &disk->state))
> 593 blk_queue_flag_set(QUEUE_FLAG_DYING, disk->queue);
>
> SCSI does not set GD_OWNS_QUEUE, so QUEUE_FLAG_DYING is not set in
> this scenario.
Yes, you're right. Please explain this in commit message as well.
>
> Thanks.
>
>>
>> Thanks,
>> Kuai
>>
>>> mutex_lock(&disk->open_mutex)
>>>
>>> This is a classic ABBA deadlock. To fix the deadlock, make sure we don't
>>> try to acquire disk->open_mutex after freezing the queue.
>>>
>>> Signed-off-by: Yang Yang <yang.yang@...o.com>
>>> ---
>>> block/genhd.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/block/genhd.c b/block/genhd.c
>>> index 8f1f3c6b4d67..c5fca3e893a0 100644
>>> --- a/block/genhd.c
>>> +++ b/block/genhd.c
>>> @@ -663,12 +663,12 @@ void del_gendisk(struct gendisk *disk)
>>> */
>>> if (!test_bit(GD_DEAD, &disk->state))
>>> blk_report_disk_dead(disk, false);
>>> - __blk_mark_disk_dead(disk);
>>> /*
>>> * Drop all partitions now that the disk is marked dead.
>>> */
>>> mutex_lock(&disk->open_mutex);
>>> + __blk_mark_disk_dead(disk);
>>> xa_for_each_start(&disk->part_tbl, idx, part, 1)
>>> drop_partition(part);
>>> mutex_unlock(&disk->open_mutex);
Take a look at del_gendisk(), between freeze and unfreeze queue, I
notice that there is also device_del() here, which means it will wait
for all sysfs readers/writers to be done, so related sysfs api can't
issue IO to trigger blk_queue_enter(). And this behaviour does't look
reasonable, we never forbit this.
Then take a look at scsi sysfs api, I notice that scsi_rescan_device()
can be called and issue IO. Hence other than the 'open_mutex', same
deadlock still exist:
t1: t2
store_state_field
scsi_rescan_device
scsi_attach_vpd
scsi_get_vpd_buf
scsi_vpd_inquiry
scsi_execute_cmd
del_gendisk
bdev_unhash
blk_freeze_queue_start
blk_queue_enter
device_del
kobject_del
sysfs_remove_dir
I didn't test this, just by code review, and I could be wrong. And
I don't check all the procedures between freeze and unfreeze yet.
Thanks,
Kuai
>>>
>>
>
> .
>
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