• Mike Snitzer's avatar
    dm mpath: disable WRITE SAME if it fails · f84cb8a4
    Mike Snitzer authored
    Workaround the SCSI layer's problematic WRITE SAME heuristics by
    disabling WRITE SAME in the DM multipath device's queue_limits if an
    underlying device disabled it.
    
    The WRITE SAME heuristics, with both the original commit 5db44863
    ("[SCSI] sd: Implement support for WRITE SAME") and the updated commit
    66c28f97 ("[SCSI] sd: Update WRITE SAME heuristics"), default to enabling
    WRITE SAME(10) even without successfully determining it is supported.
    After the first failed WRITE SAME the SCSI layer will disable WRITE SAME
    for the device (by setting sdkp->device->no_write_same which results in
    'max_write_same_sectors' in device's queue_limits to be set to 0).
    
    When a device is stacked ontop of such a SCSI device any changes to that
    SCSI device's queue_limits do not automatically propagate up the stack.
    As such, a DM multipath device will not have its WRITE SAME support
    disabled.  This causes the block layer to continue to issue WRITE SAME
    requests to the mpath device which causes paths to fail and (if mpath IO
    isn't configured to queue when no paths are available) it will result in
    actual IO errors to the upper layers.
    
    This fix doesn't help configurations that have additional devices
    stacked ontop of the mpath device (e.g. LVM created linear DM devices
    ontop).  A proper fix that restacks all the queue_limits from the bottom
    of the device stack up will need to be explored if SCSI will continue to
    use this model of optimistically allowing op codes and then disabling
    them after they fail for the first time.
    
    Before this patch:
    
    EXT4-fs (dm-6): mounted filesystem with ordered data mode. Opts: (null)
    device-mapper: multipath: XXX snitm debugging: got -EREMOTEIO (-121)
    device-mapper: multipath: XXX snitm debugging: failing WRITE SAME IO with error=-121
    end_request: critical target error, dev dm-6, sector 528
    dm-6: WRITE SAME failed. Manually zeroing.
    device-mapper: multipath: Failing path 8:112.
    end_request: I/O error, dev dm-6, sector 4616
    dm-6: WRITE SAME failed. Manually zeroing.
    end_request: I/O error, dev dm-6, sector 4616
    end_request: I/O error, dev dm-6, sector 5640
    end_request: I/O error, dev dm-6, sector 6664
    end_request: I/O error, dev dm-6, sector 7688
    end_request: I/O error, dev dm-6, sector 524288
    Buffer I/O error on device dm-6, logical block 65536
    lost page write due to I/O error on dm-6
    JBD2: Error -5 detected when updating journal superblock for dm-6-8.
    end_request: I/O error, dev dm-6, sector 524296
    Aborting journal on device dm-6-8.
    end_request: I/O error, dev dm-6, sector 524288
    Buffer I/O error on device dm-6, logical block 65536
    lost page write due to I/O error on dm-6
    JBD2: Error -5 detected when updating journal superblock for dm-6-8.
    
    # cat /sys/block/sdh/queue/write_same_max_bytes
    0
    # cat /sys/block/dm-6/queue/write_same_max_bytes
    33553920
    
    After this patch:
    
    EXT4-fs (dm-6): mounted filesystem with ordered data mode. Opts: (null)
    device-mapper: multipath: XXX snitm debugging: got -EREMOTEIO (-121)
    device-mapper: multipath: XXX snitm debugging: WRITE SAME I/O failed with error=-121
    end_request: critical target error, dev dm-6, sector 528
    dm-6: WRITE SAME failed. Manually zeroing.
    
    # cat /sys/block/sdh/queue/write_same_max_bytes
    0
    # cat /sys/block/dm-6/queue/write_same_max_bytes
    0
    
    It should be noted that WRITE SAME support wasn't enabled in DM
    multipath until v3.10.
    Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
    Cc: Martin K. Petersen <martin.petersen@oracle.com>
    Cc: Hannes Reinecke <hare@suse.de>
    Cc: stable@vger.kernel.org # 3.10+
    f84cb8a4
dm-mpath.c 41.3 KB