On Thu, 2015-08-27 at 20:16 +0200, mhocko@xxxxxxxxxx wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> b9d5c6b7ef57 ("[SCSI] cleanup setting task state in
Heh, it's tempting to revert that. The reason is we always need to be
interruptible state before we check the flag to avoid missing wakeups.
> 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>
> ---
> drivers/scsi/scsi_error.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
> index 6457a8a0db9c..2c0a817d5dbe 100644
> --- a/drivers/scsi/scsi_error.c
> +++ b/drivers/scsi/scsi_error.c
> @@ -2169,8 +2169,11 @@ int scsi_error_handler(void *data)
> * We never actually get interrupted because kthread_run
> * disables signal delivery for the created thread.
> */
> - while (!kthread_should_stop()) {
> + while (true) {
Comment here, I think, please to avoid any other erroneous tidying
attempts. How about
/*
* The sequence in kthread_stop() sets the stop flag first then
* wakes the process. To avoid missed wakeups, the task should always
* be in a non running state before the stop flag is checked
*/
Otherwise this looks fine.
James
> set_current_state(TASK_INTERRUPTIBLE);
> + if (kthread_should_stop())
> + break;
> +
> if ((shost->host_failed == 0 && shost->host_eh_scheduled == 0) ||
> shost->host_failed != atomic_read(&shost->host_busy)) {
> SCSI_LOG_ERROR_RECOVERY(1,
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