linux-kernel - Re: [PATCH 1/2] block: export __blk_complete

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Date:   Fri, 15 Jun 2018 11:20:40 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     "jianchao.wang" <jianchao.w.wang@...cle.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
        James Bottomley <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-block <linux-block@...r.kernel.org>,
        Linux SCSI List <linux-scsi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] block: export __blk_complete_request

On Fri, Jun 15, 2018 at 11:04 AM, jianchao.wang
<jianchao.w.wang@...cle.com> wrote:
> Hi Ming
>
> Thanks for your kindly response.
>
> On 06/15/2018 10:56 AM, Ming Lei wrote:
>>>> IMO, ref-counter is just to fix the blk-mq req life recycle issue.
>>>> It cannot replace the blk_mark_rq_complete which could avoid the race between
>>>> timeout and io completion path.
>>> The .timeout return BLK_EH_DONE doesn't always mean the request has been completed.
>>> Such as scsi-mid layer, its .timeout callback return BLK_EH_DONE but the timed out
>>> request is still in abort or eh process. What if a completion irq come during that ?
>> For blk-mq, it is avoided by the atomic state change in
>> __blk_mq_complete_request(),
>> that is why I mentioned the question in my last reply.
>>
>
> but blk_mq_check_expired doesn't do that.
> do I miss anything ?

Right, that is the difference between blk-mq and legacy now, then if scsi-mq
drivers can work well, they should work well with the following change in the
non-mq mode:

diff --git a/block/blk-timeout.c b/block/blk-timeout.c
index 4b8a48d48ba1..9fce09d55652 100644
--- a/block/blk-timeout.c
+++ b/block/blk-timeout.c
@@ -88,7 +88,6 @@ static void blk_rq_timed_out(struct request *req)
        switch (ret) {
        case BLK_EH_RESET_TIMER:
                blk_add_timer(req);
-               blk_clear_rq_complete(req);
                break;
        case BLK_EH_DONE:
                /*
@@ -115,8 +114,7 @@ static void blk_rq_check_expired(struct request
*rq, unsigned long *next_timeout
                /*
                 * Check if we raced with end io completion
                 */
-               if (!blk_mark_rq_complete(rq))
-                       blk_rq_timed_out(rq);
+               blk_rq_timed_out(rq);
        } else if (!*next_set || time_after(*next_timeout, deadline)) {
                *next_timeout = deadline;
                *next_set = 1;


Thanks,
Ming Lei