[PATCH v4 0/1] multipathd: recheck WWIDs of re-added paths with the device

[Brian Bunker <brian@purestorage.com>]

During an array controller failover on an iSCSI host, multipathd
briefly put a path to one LUN into the map of another LUN, and I/O
meant for the first LUN landed on the second. See the v1 cover letter
for the full sequence, and my reply to Martin on v3 for the open
questions about it.

In short: a change uevent reported the wrong WWID for one path. The
removal of the path from its map then blocked for 4.4 seconds while
the map was suspended, and the re-add used that same, by then 4.4
second old, uevent to put the path into the wrong map. The next
INQUIRY on the path, 140 ms after the re-add, returned the correct
WWID.

Changes in v4, after Martin's and Ben's review of v3:

- Back to SG_IO, as in v2. The re-add check reads VPD page 0x83 from
  the device with check_path_wwid_change(), the same function
  recheck_wwid already uses, instead of comparing with the cached
  sysfs page. The cached page can be stale, so it isn't a better
  reference than udev's own INQUIRY.

- The check only runs if recheck_wwid is set. It is off by default,
  so nothing changes for users who don't enable it.

- Still only on PATH_ADD_REINIT, i.e. only for the re-add at the end
  of uev_update_path(). Ordinary adds never run it.

- No changes to libmultipath. get_sysfs_wwid() and the ABI version
  bump from v3 are gone.

- The uev_update_path() check from v2 that ignored a changed udev WWID
  stays dropped.

- multipath.conf(5) documents the new case under recheck_wwid.

We've seen the problem once and haven't reproduced it. We have been
running a v1-style patch on our test initiators since then without a
recurrence, which at this rate doesn't prove much either way.


Brian Bunker (1):
  multipathd: recheck WWIDs of re-added paths with the device

 multipath/multipath.conf.5.in |  8 +++++---
 multipathd/cli_handlers.c     |  2 +-
 multipathd/main.c             | 37 ++++++++++++++++++++++++-----------
 multipathd/main.h             | 13 +++++++++++-
 4 files changed, 44 insertions(+), 16 deletions(-)

-- 
2.56.0