From: Alan Stern <stern@rowland.harvard.edu>
To: Martin Kepplinger <martin.kepplinger@puri.sm>
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>,
Bart Van Assche <bvanassche@acm.org>,
Can Guo <cang@codeaurora.org>,
martin.petersen@oracle.com, linux-scsi@vger.kernel.org,
linux-kernel@vger.kernel.org, kernel@puri.sm
Subject: Re: [PATCH] scsi: sd: add runtime pm to open / release
Date: Sat, 8 Aug 2020 11:05:42 -0400 [thread overview]
Message-ID: <20200808150542.GB256751@rowland.harvard.edu> (raw)
In-Reply-To: <b0abab28-880e-4b88-eb3c-9ffd927d1ed9@puri.sm>
On Sat, Aug 08, 2020 at 08:59:09AM +0200, Martin Kepplinger wrote:
> On 07.08.20 16:30, Alan Stern wrote:
> > On Fri, Aug 07, 2020 at 11:51:21AM +0200, Martin Kepplinger wrote:
> >> it's really strange: below is the change I'm trying. Of course that's
> >> only for testing the functionality, nothing how a patch could look like.
> >>
> >> While I remember it had worked, now (weirdly since I tried that mounting
> >> via fstab) it doesn't anymore!
> >>
> >> What I understand (not much): I handle the error with "retry" via the
> >> new flag, but scsi_decide_disposition() returns SUCCESS because of "no
> >> more retries"; but it's the first and only time it's called.
> >
> > Are you saying that scmd->allowed is set to 0? Or is scsi_notry_cmd()
> > returning a nonzero value? Whichever is true, why does it happen that
> > way?
>
> scsi_notry_cmd() is returning 1. (it's retry 1 of 5 allowed).
>
> why is it returning 1? REQ_FAILFAST_DEV is set. It's DID_OK, then "if
> (status_byte(scmd->result) != CHECK_CONDITION)" appearently is not true,
> then at the end it returns 1 because of REQ_FAILFAST_DEV.
>
> that seems to come from the block layer. why and when? could I change
> that so that the scsi error handling stays in control?
The only place I see where that flag might get set is in
blk_mq_bio_to_request() in block/blk-mq.c, which does:
if (bio->bi_opf & REQ_RAHEAD)
rq->cmd_flags |= REQ_FAILFAST_MASK;
So apparently read-ahead reads are supposed to fail fast (i.e., without
retries), presumably because they are optional after all.
> > What is the failing command? Is it a READ(10)?
>
> Not sure how I'd answer that, but here's the test to trigger the error:
>
> mount /dev/sda1 /mnt
> cd /mnt
> ls
> cp file ~/ (if ls "works" and doesn't yet trigger the error)
>
> and that's the (familiar looking) logs when doing so. again: despite the
> mentioned workaround in scsi_error and the new expected_media_change
> flag *is* set and gets cleared, as it should be. REQ_FAILFAST_DEV seems
> to override what I want to do is scsi_error:
>
> [ 55.557629] sd 0:0:0:0: [sda] tag#0 UNKNOWN(0x2003) Result:
> hostbyte=0x00 driverbyte=0x08 cmd_age=0s
> [ 55.557639] sd 0:0:0:0: [sda] tag#0 Sense Key : 0x6 [current]
> [ 55.557646] sd 0:0:0:0: [sda] tag#0 ASC=0x28 ASCQ=0x0
> [ 55.557657] sd 0:0:0:0: [sda] tag#0 CDB: opcode=0x28 28 00 00 08 fc
> e0 00 00 01 00
Yes, 0x28 is READ(10). Likely this is a read-ahead request, although I
don't know how we can tell for sure.
> [ 55.557666] blk_update_request: I/O error, dev sda, sector 589024 op
> 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0
> [ 55.568899] sd 0:0:0:0: [sda] tag#0 device offline or changed
> [ 55.574691] blk_update_request: I/O error, dev sda, sector 589025 op
> 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0
> [ 55.585756] sd 0:0:0:0: [sda] tag#0 device offline or changed
> [ 55.591562] blk_update_request: I/O error, dev sda, sector 589026 op
> 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0
> [ 55.602274] sd 0:0:0:0: [sda] tag#0 device offline or changed
> (... goes on with the same)
Is such a drastic response really appropriate for the failure of a
read-ahead request? It seems like a more logical response would be to
let the request fail but keep the device online.
Of course, that would only solve part of your problem -- your log would
still get filled with those "I/O error" messages even though they
wouldn't be fatal. Probably a better approach would be to make the new
expecting_media_change flag override scsi_no_retry_cmd().
But this is not my area of expertise. Maybe someone else will have more
to say.
Alan Stern
next prev parent reply other threads:[~2020-08-08 15:05 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-23 11:10 [PATCH] scsi: sd: add runtime pm to open / release Martin Kepplinger
2020-06-24 13:33 ` Bart Van Assche
2020-06-25 8:16 ` Martin Kepplinger
2020-06-25 14:52 ` Alan Stern
2020-06-26 3:53 ` Bart Van Assche
2020-06-26 15:07 ` Bart Van Assche
2020-06-26 15:44 ` Alan Stern
2020-06-28 2:37 ` Bart Van Assche
2020-06-28 13:10 ` Alan Stern
2020-06-29 9:42 ` Martin Kepplinger
2020-06-29 16:15 ` Alan Stern
2020-06-29 16:56 ` Bart Van Assche
2020-06-29 17:40 ` Alan Stern
2020-06-30 3:33 ` Martin Kepplinger
2020-06-30 13:38 ` Alan Stern
2020-06-30 15:59 ` Bart Van Assche
2020-06-30 18:02 ` Alan Stern
2020-06-30 19:23 ` Bart Van Assche
2020-06-30 19:38 ` Alan Stern
2020-06-30 23:31 ` Bart Van Assche
2020-07-01 0:49 ` Alan Stern
2020-07-06 16:41 ` Alan Stern
2020-07-28 7:02 ` Martin Kepplinger
2020-07-28 20:02 ` Alan Stern
2020-07-29 14:12 ` Martin Kepplinger
2020-07-29 14:32 ` Alan Stern
2020-07-29 14:44 ` Martin K. Petersen
2020-07-29 14:56 ` Alan Stern
2020-07-29 14:46 ` James Bottomley
2020-07-29 14:53 ` James Bottomley
2020-07-29 15:40 ` Martin Kepplinger
2020-07-29 15:44 ` James Bottomley
2020-07-29 16:43 ` Martin Kepplinger
2020-07-29 18:25 ` Alan Stern
2020-07-29 18:29 ` James Bottomley
2020-07-30 8:52 ` Martin Kepplinger
2020-07-30 8:54 ` Martin Kepplinger
2020-07-30 15:10 ` Alan Stern
2020-08-04 9:39 ` Martin Kepplinger
2020-08-07 9:51 ` Martin Kepplinger
2020-08-07 14:30 ` Alan Stern
2020-08-08 6:59 ` Martin Kepplinger
2020-08-08 15:05 ` Alan Stern [this message]
2020-08-09 9:20 ` Martin Kepplinger
2020-08-09 15:26 ` Alan Stern
2020-08-10 12:03 ` Martin Kepplinger
2020-08-10 14:13 ` Alan Stern
2020-08-11 7:55 ` Martin Kepplinger
2020-08-11 13:48 ` Alan Stern
2020-08-23 14:57 ` [PATCH] block: Fix bug in runtime-resume handling Alan Stern
2020-08-24 17:48 ` Bart Van Assche
2020-08-24 20:13 ` Alan Stern
2020-08-26 7:48 ` Martin Kepplinger
2020-08-27 17:42 ` Martin Kepplinger
2020-08-27 20:29 ` Alan Stern
2020-08-29 7:24 ` Martin Kepplinger
2020-08-29 15:26 ` Alan Stern
2020-08-29 16:33 ` Martin Kepplinger
2020-08-29 18:56 ` Alan Stern
2020-08-30 0:38 ` Bart Van Assche
2020-08-30 1:06 ` Alan Stern
2020-07-29 15:40 ` [PATCH] scsi: sd: add runtime pm to open / release Alan Stern
2020-07-29 15:49 ` James Bottomley
2020-07-29 16:17 ` Alan Stern
2020-07-29 15:52 ` Martin Kepplinger
2020-07-29 18:10 ` Douglas Gilbert
2020-07-30 8:05 ` Martin Kepplinger
2020-07-30 15:14 ` Alan Stern
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