Re: [PATCH v4] scsi: ufs: Cleanup completed request without interrupt notification

Can Guo
2020-07-31T08:02:44Z

Hi Bart,

On 2020-07-31 12:06, Bart Van Assche wrote:
> On 2020-07-30 18:30, Stanley Chu wrote:
>> On Mon, 2020-07-27 at 11:18 +0000, Avri Altman wrote:
>>> Looks good to me.
>>> But better wait and see if Bart have any further reservations.
>>
>> Would you have any further suggestions?
>
> Today is the first time that I took a look at ufshcd_abort(). The
> approach of that function looks wrong to me. This is how I think that a
> SCSI LLD abort handler should work:
> (1) Serialize against the completion path
> (__ufshcd_transfer_req_compl()) such that it cannot happen that the
> abort handler and the regular completion path both call
> cmd->scsi_done(cmd) at the same time. I'm not sure whether an existing
> synchronization object can be used for this purpose or whether a new
> synchronization object has to be introduced to serialize scsi_done()
> calls from __ufshcd_transfer_req_compl() and ufshcd_abort().
> (2) While holding that synchronization object, check whether the SCSI
> command is still outstanding. If so, submit a SCSI abort TMR to the
> device.
> (3) If the command has been aborted, call scsi_done() and return
> SUCCESS. If aborting failed and the command is still in progress,
> return
> FAILED.
>
> An example is available in srp_abort() in
> drivers/infiniband/ulp/srp/ib_srp.c.
>
> Bart.

AFAIK, sychronization of scsi_done is not a problem here, because scsi
layer
use the atomic state, namely SCMD_STATE_COMPLETE, of a scsi cmd to
prevent
the concurrency of abort and real completion of it.

Check func scsi_times_out(), hope it helps.

enum blk_eh_timer_return scsi_times_out(struct request *req)
{
...
if (rtn == BLK_EH_DONE) {
/*
* Set the command to complete first in order to prevent
a real
* completion from releasing the command while error
handling
* is using it. If the command was already completed,
then the
* lower level driver beat the timeout handler, and it
is safe
* to return without escalating error recovery.
*
* If timeout handling lost the race to a real
completion, the
* block layer may ignore that due to a fake timeout
injection,
* so return RESET_TIMER to allow error handling another
shot
* at this command.
*/
if (test_and_set_bit(SCMD_STATE_COMPLETE, &scmd->state))
return BLK_EH_RESET_TIMER;
if (scsi_abort_command(scmd) != SUCCESS) {
set_host_byte(scmd, DID_TIME_OUT);
scsi_eh_scmd_add(scmd);
}
}
}

Thanks,

Can Guo.