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author | David Jeffery <djeffery@redhat.com> | 2019-12-17 17:00:24 +0100 |
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committer | Jens Axboe <axboe@kernel.dk> | 2019-12-21 00:51:54 +0100 |
commit | df034c93f15ee71df231ff9fe311d27ff08a2a52 (patch) | |
tree | e2fbdcea808a7a2f596ff91f788de7835a94d7b4 /init/do_mounts_md.c | |
parent | block: fix memleak when __blk_rq_map_user_iov() is failed (diff) | |
download | linux-df034c93f15ee71df231ff9fe311d27ff08a2a52.tar.xz linux-df034c93f15ee71df231ff9fe311d27ff08a2a52.zip |
sbitmap: only queue kyber's wait callback if not already active
Under heavy loads where the kyber I/O scheduler hits the token limits for
its scheduling domains, kyber can become stuck. When active requests
complete, kyber may not be woken up leaving the I/O requests in kyber
stuck.
This stuck state is due to a race condition with kyber and the sbitmap
functions it uses to run a callback when enough requests have completed.
The running of a sbt_wait callback can race with the attempt to insert the
sbt_wait. Since sbitmap_del_wait_queue removes the sbt_wait from the list
first then sets the sbq field to NULL, kyber can see the item as not on a
list but the call to sbitmap_add_wait_queue will see sbq as non-NULL. This
results in the sbt_wait being inserted onto the wait list but ws_active
doesn't get incremented. So the sbitmap queue does not know there is a
waiter on a wait list.
Since sbitmap doesn't think there is a waiter, kyber may never be
informed that there are domain tokens available and the I/O never advances.
With the sbt_wait on a wait list, kyber believes it has an active waiter
so cannot insert a new waiter when reaching the domain's full state.
This race can be fixed by only adding the sbt_wait to the queue if the
sbq field is NULL. If sbq is not NULL, there is already an action active
which will trigger the re-running of kyber. Let it run and add the
sbt_wait to the wait list if still needing to wait.
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: David Jeffery <djeffery@redhat.com>
Reported-by: John Pittman <jpittman@redhat.com>
Tested-by: John Pittman <jpittman@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'init/do_mounts_md.c')
0 files changed, 0 insertions, 0 deletions