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author | Mike Snitzer <snitzer@redhat.com> | 2020-05-27 16:32:51 -0400 |
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committer | Mike Snitzer <snitzer@redhat.com> | 2020-06-05 14:59:56 -0400 |
commit | 553ec94cb4b4937b48f81e27de33f71325d1a227 (patch) | |
tree | a344fd73d12ab0e6fb78fc270832163d314a76ca /drivers/ipack/ipack.c | |
parent | a862e4e2154289fc12aa9e70f33614d9c70f3be4 (diff) |
dm mpath: restrict queue_if_no_path state machine
Do not allow saving disabled queue_if_no_path if already saved as
enabled; implies multiple suspends (which shouldn't ever happen). Log
if this unlikely scenario is ever triggered.
Also, only write MPATHF_SAVED_QUEUE_IF_NO_PATH during presuspend or if
"fail_if_no_path" message. MPATHF_SAVED_QUEUE_IF_NO_PATH is no longer
always modified, e.g.: even if queue_if_no_path()'s save_old_value
argument wasn't set. This just implies a bit tighter control over
the management of MPATHF_SAVED_QUEUE_IF_NO_PATH. Side-effect is
multipath_resume() doesn't reset MPATHF_QUEUE_IF_NO_PATH unless
MPATHF_SAVED_QUEUE_IF_NO_PATH was set (during presuspend); and at that
time the MPATHF_SAVED_QUEUE_IF_NO_PATH bit gets cleared. So
MPATHF_SAVED_QUEUE_IF_NO_PATH's use is much more narrow in scope.
Last, but not least, do _not_ disable queue_if_no_path during noflush
suspend. There is no need/benefit to saving off queue_if_no_path via
MPATHF_SAVED_QUEUE_IF_NO_PATH and clearing MPATHF_QUEUE_IF_NO_PATH for
noflush suspend -- by avoiding this needless queue_if_no_path flag
churn there is less potential for MPATHF_QUEUE_IF_NO_PATH to get lost.
Which avoids potential for IOs to be errored back up to userspace
during DM multipath's handling of path failures.
That said, this last change papers over a reported issue concerning
request-based dm-multipath's interaction with blk-mq, relative to
suspend and resume: multipath_endio is being called _before_
multipath_resume. This should never happen if DM suspend's
blk_mq_quiesce_queue() + dm_wait_for_completion() is genuinely waiting
for all inflight blk-mq requests to complete. Similarly:
drivers/md/dm.c:__dm_resume() clearly calls dm_table_resume_targets()
_before_ dm_start_queue()'s blk_mq_unquiesce_queue() is called. If
the queue isn't even restarted until after multipath_resume(); the BIG
question that still needs answering is: how can multipath_end_io beat
multipath_resume in a race!?
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Diffstat (limited to 'drivers/ipack/ipack.c')
0 files changed, 0 insertions, 0 deletions