linux-kernel - [PATCH] blk-mq: Directly schedule q->timeout

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Message-ID: <20180402220458.GJ388343@devbig577.frc2.facebook.com>
Date:   Mon, 2 Apr 2018 15:04:58 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Sitsofe Wheeler <sitsofe@...il.com>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org,
        Stefan Haberland <sth@...ux.vnet.ibm.com>,
        Jan Hoeppner <hoeppner@...ux.vnet.ibm.com>,
        Bart Van Assche <Bart.VanAssche@....com>
Subject: [PATCH] blk-mq: Directly schedule q->timeout_work when aborting a
 request

Request abortion is performed by overriding deadline to now and
scheduling timeout handling immediately.  For the latter part, the
code was using mod_timer(timeout, 0) which can't guarantee that the
timer runs afterwards.  Let's schedule the underlying work item
directly instead.

This fixes the hangs during probing reported by Sitsofe but it isn't
yet clear to me how the failure can happen reliably if it's just the
above described race condition.

Signed-off-by: Tejun Heo <tj@...nel.org>
Reported-by: Sitsofe Wheeler <sitsofe@...il.com>
Reported-by: Meelis Roos <mroos@...ux.ee>
Fixes: 358f70da49d7 ("blk-mq: make blk_abort_request() trigger timeout path")
Cc: stable@...r.kernel.org # v4.16
Link: http://lkml.kernel.org/r/CALjAwxh-PVYFnYFCJpGOja+m5SzZ8Sa4J7ohxdK=r8NyOF-EMA@mail.gmail.com
Link: http://lkml.kernel.org/r/alpine.LRH.2.21.1802261049140.4893@math.ut.ee
---
Hello,

I don't have the full explanation yet but here's a preliminary patch.

Thanks.

 block/blk-timeout.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-timeout.c b/block/blk-timeout.c
index a05e367..f0e6e41 100644
--- a/block/blk-timeout.c
+++ b/block/blk-timeout.c
@@ -165,7 +165,7 @@ void blk_abort_request(struct request *req)
 		 * No need for fancy synchronizations.
 		 */
 		blk_rq_set_deadline(req, jiffies);
-		mod_timer(&req->q->timeout, 0);
+		kblockd_schedule_work(&req->q->timeout_work);
 	} else {
 		if (blk_mark_rq_complete(req))
 			return;