Re: [PATCH v2 2/2] scsi: sd: Rework asynchronous resume support

[Bart Van Assche]

On 8/12/22 03:48, Geert Uytterhoeven wrote:
> sd_submit_start() is called once during suspend, and once during
> resume.  It does not hang.
>
> Reading from /dev/sda hangs after resume (not in sd_submit_start(),
> which is never called for reading).
>
> Two tasks are blocked in blk_mq_get_tag() calling io_schedule():
>
> task:kworker/7:1     state:D stack:    0 pid:  122 ppid:     2 flags:0x00000008
> Workqueue: events ata_scsi_dev_rescan
> Call trace:
>   __switch_to+0xbc/0x124
>   __schedule+0x540/0x71c
>   schedule+0x58/0xa0
>   io_schedule+0x18/0x34
>   blk_mq_get_tag+0x138/0x244
>   __blk_mq_alloc_requests+0x130/0x2f0
>   blk_mq_alloc_request+0x74/0xa8
>   scsi_alloc_request+0x10/0x30
>   __scsi_execute+0x5c/0x18c
>   scsi_vpd_inquiry+0x7c/0xdc
>   scsi_get_vpd_size+0x34/0xa8
>   scsi_get_vpd_buf+0x28/0xf4
>   scsi_attach_vpd+0x44/0x170
>   scsi_rescan_device+0x30/0x98
>   ata_scsi_dev_rescan+0xc8/0xfc
>   process_one_work+0x2e0/0x474
>   worker_thread+0x1cc/0x270
>   kthread+0xd8/0xe8
>   ret_from_fork+0x10/0x20
>
>
> task:hd              state:D stack:    0 pid: 1163 ppid:  1076 flags:0x00000000
> Call trace:
>   __switch_to+0xbc/0x124
>   __schedule+0x540/0x71c
>   schedule+0x58/0xa0
>   io_schedule+0x18/0x34
>   blk_mq_get_tag+0x138/0x244
>   __blk_mq_alloc_requests+0x130/0x2f0
>   blk_mq_submit_bio+0x44c/0x5b4
>   __submit_bio+0x24/0x5c
>   submit_bio_noacct_nocheck+0x8c/0x178
>   submit_bio_noacct+0x380/0x3b0
>   submit_bio+0x34/0x3c
>   mpage_bio_submit+0x28/0x38
>   mpage_readahead+0xa8/0x178
>   blkdev_readahead+0x14/0x1c
>   read_pages+0x4c/0x158
>   page_cache_ra_unbounded+0xd8/0x174
>   do_page_cache_ra+0x40/0x4c
>   page_cache_ra_order+0x14/0x1c
>   ondemand_readahead+0x124/0x2fc
>   page_cache_sync_ra+0x50/0x54
>   filemap_read+0x130/0x6e8
>   blkdev_read_iter+0xf0/0x164
>   new_sync_read+0x74/0xc0
>   vfs_read+0xbc/0xd8
>   ksys_read+0x6c/0xd4
>   __arm64_sys_read+0x14/0x1c
>   invoke_syscall+0x70/0xf4
>   el0_svc_common.constprop.0+0xbc/0xf0
>   do_el0_svc+0x18/0x20
>   el0_svc+0x30/0x84
>   el0t_64_sync_handler+0x90/0xf8
>   el0t_64_sync+0x14c/0x150

Hi Geert,

All that can be concluded from the above is that blk_mq_get_tag() is 
waiting for other I/O request(s) to finish. One or more other requests 
are in progress and either scsi_done() has not been called for these 
requests or the error handler got stuck. Since the issue reported above 
is not observed with other ATA interfaces, this may be related to the 
ATA interface driver used in your test setup.

Bart.