On 11/29/20 11:23 PM, Yufen Yu wrote: > We reported IO stuck on a scsi usb driver recently and any IO issued > to the device cannot return. The usb driver just have **one** driver tag > and **two** sched tag. After debugging, we found there is a deadlock > race as following: > > cpu0(scsi_eh) cpu1 cpu2 > get sched tag(internal_tag=0) > get driver tag(tag=0) > get sched > tag(internal_tag=1) > wait for driver tag > scsi_error_handler try issue io > wait for sched tag > try to dispatch the request > wait for setting shost state as SHOST_RUNNING > //scsi_host_set_state(shost, SHOST_RUNNING) > > The scsi_eh thread stack as following: > PID: 945745 TASK: ffff950a8f2f0000 CPU: 42 COMMAND: "scsi_eh_15" > [ffffbbee8d5b3ce0] __schedule at ffffffffa506ebac > [ffffbbee8d5b3d00] sbitmap_get at ffffffffa4c4684f > [ffffbbee8d5b3d48] schedule at ffffffffa506f208 > [ffffbbee8d5b3d50] io_schedule at ffffffffa506f5d2 > [ffffbbee8d5b3d60] blk_mq_get_tag at ffffffffa4bf5277 > [ffffbbee8d5b3d88] autoremove_wake_function at ffffffffa48ffe40 > [ffffbbee8d5b3db8] autoremove_wake_function at ffffffffa48ffe40 > [ffffbbee8d5b3e08] blk_mq_get_request at ffffffffa4bef14c > [ffffbbee8d5b3e20] eh_lock_door_done at ffffffffa4da5580 > [ffffbbee8d5b3e38] blk_mq_alloc_request at ffffffffa4bef494 > [ffffbbee8d5b3e80] blk_get_request at ffffffffa4be5042 > [ffffbbee8d5b3e98] scsi_error_handler at ffffffffa4da8670 > [ffffbbee8d5b3ea0] __schedule at ffffffffa506ebb4 > [ffffbbee8d5b3f08] scsi_error_handler at ffffffffa4da8430 > [ffffbbee8d5b3f10] kthread at ffffffffa48d6d7d > [ffffbbee8d5b3f20] kthread at ffffffffa48d6c70 > [ffffbbee8d5b3f50] ret_from_fork at ffffffffa520023f > > Since there are no more available sched tag and driver tag. All of > threads will wait forever. We found the bug on 4.18 kernel, but the > latest kernel code also have the problem. > > I don't have good idea about how to fix the bug. So, any suggestions are > welcome. Please take a look at https://lore.kernel.org/linux-scsi/20201130024615.29171-6-bvanassche@xxxxxxx/T/#u. Thanks, Bart.
