Re: [PATCH] scsi: fix scsi_error_handler vs. scsi_host_dev_release race

[Dan Williams]

On Thu, Aug 27, 2015 at 11:16 AM,  <mhocko@xxxxxxxxxx> wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> b9d5c6b7ef57 ("[SCSI] cleanup setting task state in
> scsi_error_handler()") has introduced a race between scsi_error_handler
> and scsi_host_dev_release resulting in the hang when the device goes
> away because scsi_error_handler might miss a wake up:
>
> CPU0                                    CPU1
> scsi_error_handler                      scsi_host_dev_release
>                                           kthread_stop()
>   kthread_should_stop()
>     test_bit(KTHREAD_SHOULD_STOP)
>                                             set_bit(KTHREAD_SHOULD_STOP)
>                                             wake_up_process()
>                                             wait_for_completion()
>
>   set_current_state(TASK_INTERRUPTIBLE)
>   schedule()
>
> The most straightforward solution seems to be to invert the ordering of
> the set_current_state and kthread_should_stop.
>
> The issue has been noticed during reboot test on a 3.0 based kernel but
> the current code seems to be affected in the same way.
>
> Cc: stable # 3.6+
> Reported-and-Debugged-by: Mike Mayer <Mike.Meyer@xxxxxxxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>

Acked-by: Dan Williams <dan.j.williams@xxxxxxxxx>
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