diff options
author | Damien Le Moal <damien.lemoal@wdc.com> | 2019-08-28 13:40:20 +0900 |
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committer | Jens Axboe <axboe@kernel.dk> | 2019-09-03 07:59:51 -0600 |
commit | cb8acabbe33b110157955a7425ee876fb81e6bbc (patch) | |
tree | e1822764e1203e47b2f0a469582bf25a58a6886d /block/blk-iolatency.c | |
parent | 0feacaa21634014148068035b02eade71f853496 (diff) |
block: mq-deadline: Fix queue restart handling
Commit 7211aef86f79 ("block: mq-deadline: Fix write completion
handling") added a call to blk_mq_sched_mark_restart_hctx() in
dd_dispatch_request() to make sure that write request dispatching does
not stall when all target zones are locked. This fix left a subtle race
when a write completion happens during a dispatch execution on another
CPU:
CPU 0: Dispatch CPU1: write completion
dd_dispatch_request()
lock(&dd->lock);
...
lock(&dd->zone_lock); dd_finish_request()
rq = find request lock(&dd->zone_lock);
unlock(&dd->zone_lock);
zone write unlock
unlock(&dd->zone_lock);
...
__blk_mq_free_request
check restart flag (not set)
-> queue not run
...
if (!rq && have writes)
blk_mq_sched_mark_restart_hctx()
unlock(&dd->lock)
Since the dispatch context finishes after the write request completion
handling, marking the queue as needing a restart is not seen from
__blk_mq_free_request() and blk_mq_sched_restart() not executed leading
to the dispatch stall under 100% write workloads.
Fix this by moving the call to blk_mq_sched_mark_restart_hctx() from
dd_dispatch_request() into dd_finish_request() under the zone lock to
ensure full mutual exclusion between write request dispatch selection
and zone unlock on write request completion.
Fixes: 7211aef86f79 ("block: mq-deadline: Fix write completion handling")
Cc: stable@vger.kernel.org
Reported-by: Hans Holmberg <Hans.Holmberg@wdc.com>
Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-iolatency.c')
0 files changed, 0 insertions, 0 deletions