linux-kernel - Re: blk-mq timeout question

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Message-ID: <CACVXFVOgyca425hSqJws8N4L2tVZ7hq=-eO+Z1=X0jtVcJFhyA@mail.gmail.com>
Date:   Mon, 10 Jul 2017 10:23:59 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     Stefan Haberland <sth@...ux.vnet.ibm.com>
Cc:     Jens Axboe <axboe@...com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: blk-mq timeout question

On Fri, Jul 7, 2017 at 9:45 PM, Stefan Haberland <sth@...ux.vnet.ibm.com> wrote:
> While changing the DASD device driver to use the blk-mq interfaces I found
> the following unexpected behavior:
>
> In case of a timeout our complete callback is never called. Here is the
> sequence of events as I understood:
>
> - timeout occurs
> - blk_mq_check_expired() calls and checks blk_mark_rq_complete()
> - our .timeout callback is called which returns BLK_EH_NOT_HANDLED and
> schedules delayed work
> - our worker calls blk_mq_complete_request()
> - this also checks blk_mark_rq_complete() and therefore never calls our
> complete callback
>
> Question:
> Should blk_clear_rq_complete() also be called for the BLK_EH_NOT_HANDLED
> case?

>From comment in blk_rq_timed_out():

        case BLK_EH_NOT_HANDLED:
                /*
                 * LLD handles this for now but in the future
                 * we can send a request msg to abort the command
                 * and we can move more of the generic scsi eh code to
                 * the blk layer.

Looks you can/should handle the case inside DASD, and not do that in blk layer.


-- 
Ming Lei