Hi Tejun,
Sorry for sending so many emails yesterday; I blame the dental anaesthetic
I received in the morning for being so jumpy on the send button ;-)
> Can you please instrument the followings?
>
> * print the caller of scsi_eh_wakeup(). "%pF" w/ (void *)_RET_IP_
> should do it.
>
> * print why scsi_eh is going back to sleep immediately.
> ie. shost->host_failed, host_eh_scheduled, host_busy in
> scsi_error_handler(). It would also be nice to add some printks
> around schedule() and enable PRINTK_TIME.
I can certainly try this. Could you confirm whether my thoughts about a race
between the scsi_eh thread and the wake-up are plausible? I backtracked
yesterday because I thought the scsi_eh thread would get rescheduled naturally,
not realising that when the task state is TASK_INTERRUPTIBLE schedule() takes
the task off the run queue (so it needs to be explicitly woken.)
Here is my thinking again:
shost->host_eh_scheduled is read here in scsi_error_handler:
set_current_state(TASK_INTERRUPTIBLE);
while (!kthread_should_stop()) {
if ((shost->host_failed == 0 && shost->host_eh_scheduled == 0) ||
There's no locking in scsi_error_handler (though functions it calls probably
claim locks.)
When scheduling an EH, scsi_schedule_eh takes the shost->host_lock, increments
shost->host_eh_scheduled, and then wakes the EH thread. If this happens
between the scsi_eh thread reading host_eh_scheduled and sending itself back
to sleep (when the scsi_eh thread's state is TASK_INTERRUPTIBLE) nothing will
wake up the thread again and host_eh_scheduled will not get inspected.
host_eh_scheduled is stuck at 1 with the scsi_eh thread asleep, and it won't
get woken again because the ata port has been frozen and irqs are masked off.
Bruce.
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