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Message-ID: <51411297-f579-4229-a72c-c5bd5f27df34@vivo.com>
Date: Wed, 17 Jul 2024 18:15:08 +0800
From: YangYang <yang.yang@...o.com>
To: 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
On 2024/7/17 11:53, Yu Kuai wrote:
> 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.
Got it.
>>
>> 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.
These sysfs nodes are in different directories, the scsi node located
at /sys/bus/scsi/devices/0:0:0:0 and the gendisk node located at
/sys/block/sda. Would it be necessary to wait for the completion of
the scsi sysfs nodes' read/write operations before removing the
gendisk sysfs node?
Thanks.
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