Bug 244967

Description of problem:

While I/O on dm multipath devices , we are seeing frequent path failures which 
leads to unexpected I/O failover.

Snippet of syslog during failure :
****************************************
scsi(2:1:16) UNDERRUN status detected 0x15-0x0. 
resid=0x7fff8fff fw_resid=0x7fff8fff cdb=0x28 
os_underflow=0xf400 srb_flags=0x2
scsi(2:0:1:16) Dropped frame(s) detected 
(7fff8fff of f400 bytes)...retrying command.
scsi(2:1:16) qla2x00_done: did_error = 2,
comp-scsi= 0x15-0x0 pid=102056310.
SCSI error : <2 0 1 16> return code = 0x20000
end_request: I/O error, dev sdbm, sector 4192702
end_request: I/O error, dev sdbm, sector 4192708
device-mapper: dm-multipath: Failing path 68:0.


As per our understanding, We are seeing paths marked as failed for which it 
returns the status as DID_BUS_BUSY. What we understand here is, since IO's on 
multipath devices have BIO_RW_FAILFAST set (hence REQ_FASTFAIL ),   retries are 
not allowed at SCSI mid layer for errors such as QUEUEFULL, UNDERRUN..(as 
captured in the above syslog snippet) and so on. Is there any way to override 
this BIO_RW_FAILFAST  for retries to happen  in order to avoid unexpected path 
failure. 


Version-Release number of selected component (if applicable):


How reproducible:


Steps to Reproduce:
1. Present atleast 50 device(Logical Units) with 8 paths to the Host
2. Start I/O on those 50 deivices. 
3. Syslog captures  "SCSI error" and "dm-multipath: Failing path"
  
Actual results:
Unexpected path failure is seeing during the I/O.

Expected results:

Additional info:

1.multipath.conf setting:
        device {
        vendor                  "HP"
        product                 "HSV210"
        path_grouping_policy    group_by_prio
        getuid_callout          "/sbin/scsi_id -g -u -s /block/%n"
        path_checker            tur
        path_selector           "round-robin 0"
        prio_callout           "/sbin/mpath_prio_alua %n"
        rr_weight               uniform
        failback                immediate
        hardware_handler        "0"
        no_path_retry            60
}