Re: [PATCH v2 3/4] scsi: Avoid that .queuecommand() gets called for a quiesced SCSI device

[Bart Van Assche <Bart.VanAssche-Sjgp3cTcYWE@public.gmane.org>]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="utf-8", Size: 1726 bytes --]

On Thu, 2018-01-11 at 10:23 +0800, Ming Lei wrote:
> > not sufficient to prevent .queuecommand() calls from scsi_send_eh_cmnd().
> 
> Given it is error handling, do we need to prevent the .queuecommand() call
> in scsi_send_eh_cmnd()? Could you share us what the actual issue
> observed is from user view?

Please have a look at the kernel bug report in the description of patch 4/4 of
this series.

> > Hence surround the .queuecommand() call from the SCSI error handler with
> > blk_start_wait_if_quiesced() / blk_finish_wait_if_quiesced().
> > 
> > Note: converting the .queuecommand() call in scsi_send_eh_cmnd() into
> > code that calls blk_get_request(), e.g. scsi_execute_req(), is not an
> > option since scsi_send_eh_cmnd() can be called if all requests are
> > allocated and if no requests will make progress without aborting any
> > of these requests.
> 
> If we need to prevent the .queuecommand() in scsi_send_eh_cmnd(), what
> do you think of the approach by requeuing the EH command via
> scsi_mq_requeue_cmd()/scsi_requeue_cmd()? And the EH request will be
> dispatched finally when the queue becomes unquiesced or the STOPPED
> is cleared.

Calling scsi_mq_requeue_cmd() would trigger scsi_mq_uninit_cmd(),
blk_mq_put_driver_tag(), blk_mq_get_driver_tag() and scsi_mq_prep_fn().
That could cause scsi_eh_scmd_add() to be called multiple times for the
same SCSI command. However, that would break one of the assumptions
scsi_eh_scmd_add() is based on, namely that that function gets called
only once per SCSI command that is in progress.

Bart. N‹§²æìr¸›yúèšØb²X¬¶Ç§vØ^–)Þº{.nÇ+‰·¥Š{±­ÙšŠ{ayº\x1dʇڙë,j\a­¢f£¢·hš‹»öì\x17/oSc¾™Ú³9˜uÀ¦æå‰È&jw¨®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿïêäz¹Þ–Šàþf£¢·hšˆ§~ˆmš