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
