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 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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