On Mon, Nov 06, 2017 at 07:45:23PM +0000, Bart Van Assche wrote: > On Sat, 2017-11-04 at 08:19 -0600, Jens Axboe wrote: > > On 11/03/2017 07:55 PM, Ming Lei wrote: > > > It is very expensive to atomic_inc/atomic_dec the host wide counter of > > > host->busy_count, and it should have been avoided via blk-mq's mechanism > > > of getting driver tag, which uses the more efficient way of sbitmap queue. > > > > > > Also we don't check atomic_read(&sdev->device_busy) in scsi_mq_get_budget() > > > and don't run queue if the counter becomes zero, so IO hang may be caused > > > if all requests are completed just before the current SCSI device > > > is added to shost->starved_list. > > > > This looks like an improvement. I have added it for 4.15. > > > > Bart, does this fix your hang? > > No, it doesn't. After I had reduced starget->can_queue in the SRP initiator I > ran into the following hang while running the srp-test software: > > sysrq: SysRq : Show Blocked State > task PC stack pid father > systemd-udevd D 0 19882 467 0x80000106 > Call Trace: > __schedule+0x2fa/0xbb0 > schedule+0x36/0x90 > io_schedule+0x16/0x40 > __lock_page+0x10a/0x140 > truncate_inode_pages_range+0x4ff/0x800 > truncate_inode_pages+0x15/0x20 > kill_bdev+0x35/0x40 > __blkdev_put+0x6d/0x1f0 > blkdev_put+0x4e/0x130 > blkdev_close+0x25/0x30 > __fput+0xed/0x1f0 > ____fput+0xe/0x10 > task_work_run+0x8b/0xc0 > do_exit+0x38d/0xc70 > do_group_exit+0x50/0xd0 > get_signal+0x2ad/0x8c0 > do_signal+0x28/0x680 > exit_to_usermode_loop+0x5a/0xa0 > do_syscall_64+0x12e/0x170 > entry_SYSCALL64_slow_path+0x25/0x25 I can't reproduce your issue on IB/SRP any more against V4.14-RC4 with the following patches, and without any hang after running your 6 srp-test: 88022d7201e9 blk-mq: don't handle failure in .get_budget 826a70a08b12 SCSI: don't get target/host busy_count in scsi_mq_get_budget() 1f460b63d4b3 blk-mq: don't restart queue when .get_budget returns BLK_STS_RESOURCE 358a3a6bccb7 blk-mq: don't handle TAG_SHARED in restart 0df21c86bdbf scsi: implement .get_budget and .put_budget for blk-mq aeec77629a4a scsi: allow passing in null rq to scsi_prep_state_check() b347689ffbca blk-mq-sched: improve dispatching from sw queue de1482974080 blk-mq: introduce .get_budget and .put_budget in blk_mq_ops 63ba8e31c3ac block: kyber: check if there are requests in ctx in kyber_has_work() 7930d0a00ff5 sbitmap: introduce __sbitmap_for_each_set() caf8eb0d604a blk-mq-sched: move actual dispatching into one helper 5e3d02bbafad blk-mq-sched: dispatch from scheduler IFF progress is made in ->dispatch If you can reproduce, please provide me at least the following log first: find /sys/kernel/debug/block -name tags | xargs cat | grep busy If any pending requests arn't completed, please provide the related info in dbgfs about where is the request. -- Ming
