linux-kernel - Re: kernel BUG at drivers/scsi/scsi_error.c:197!

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Date:   Wed, 13 Jun 2018 16:35:58 +0200
From:   "hch@....de" <hch@....de>
To:     Bart Van Assche <Bart.VanAssche@....com>
Cc:     "hch@....de" <hch@....de>,
        "jianchao.w.wang@...cle.com" <jianchao.w.wang@...cle.com>,
        "randrianasulu@...il.com" <randrianasulu@...il.com>,
        "rdunlap@...radead.org" <rdunlap@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>
Subject: Re: kernel BUG at drivers/scsi/scsi_error.c:197! - git
        4.17.0-x64-08428-g7d3bf613e99a

On Wed, Jun 13, 2018 at 02:08:12PM +0000, Bart Van Assche wrote:
> __blk_mq_complete_request() is already called today by blk_mq_complete_request().
> However, it's not clear to me why that function is exported by Jianchao's patch.

True.  I had missed that the patch also started calling the new
mark_rq_complete function from the error handler.

> The SCSI error handler already waits until all pending requests have finished
> before it starts handling timed out commands. This e-mail thread started with a
> report of a crash in the SCSI error handler, which is a regression introduced in
> the v4.18 merge window.

ut-requests-again-that-are-in-the.patch
Yeah.  I've read back a bit.  If your theory of a double invocation of
the timeout handler is correct something like the patch below should sort
it out, right?

---
>From d408928360f087c0ad24e31d1d25533c698b8b35 Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@....de>
Date: Wed, 13 Jun 2018 16:25:40 +0200
Subject: blk-mq: don't time out requests again that are in the timeout handler

Signed-off-by: Christoph Hellwig <hch@....de>
---
 block/blk-mq.c         | 4 ++++
 include/linux/blkdev.h | 2 ++
 2 files changed, 6 insertions(+)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index e9da5e6a8526..8a2895fed078 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -770,6 +770,7 @@ EXPORT_SYMBOL(blk_mq_tag_to_rq);
 
 static void blk_mq_rq_timed_out(struct request *req, bool reserved)
 {
+	req->rq_flags |= RQF_TIMED_OUT;
 	if (req->q->mq_ops->timeout) {
 		enum blk_eh_timer_return ret;
 
@@ -779,6 +780,7 @@ static void blk_mq_rq_timed_out(struct request *req, bool reserved)
 		WARN_ON_ONCE(ret != BLK_EH_RESET_TIMER);
 	}
 
+	req->rq_flags &= ~RQF_TIMED_OUT;
 	blk_add_timer(req);
 }
 
@@ -788,6 +790,8 @@ static bool blk_mq_req_expired(struct request *rq, unsigned long *next)
 
 	if (blk_mq_rq_state(rq) != MQ_RQ_IN_FLIGHT)
 		return false;
+	if (rq->rq_flags & RQF_TIMED_OUT)
+		return false;
 
 	deadline = blk_rq_deadline(rq);
 	if (time_after_eq(jiffies, deadline))
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index bca3a92eb55f..fa6f11751430 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -127,6 +127,8 @@ typedef __u32 __bitwise req_flags_t;
 #define RQF_ZONE_WRITE_LOCKED	((__force req_flags_t)(1 << 19))
 /* already slept for hybrid poll */
 #define RQF_MQ_POLL_SLEPT	((__force req_flags_t)(1 << 20))
+/* ->timeout has been called, don't expire again */
+#define RQF_TIMED_OUT		((__force req_flags_t)(1 << 21))
 
 /* flags that prevent us from merging requests: */
 #define RQF_NOMERGE_FLAGS \
-- 
2.17.1