blk-iolatency: fix IO hang due to negative inflight counter
Our test reported the following stack, and vmcore showed that
->inflight counter is -1.
[
ffffc9003fcc38d0] __schedule at
ffffffff8173d95d
[
ffffc9003fcc3958] schedule at
ffffffff8173de26
[
ffffc9003fcc3970] io_schedule at
ffffffff810bb6b6
[
ffffc9003fcc3988] blkcg_iolatency_throttle at
ffffffff813911cb
[
ffffc9003fcc3a20] rq_qos_throttle at
ffffffff813847f3
[
ffffc9003fcc3a48] blk_mq_make_request at
ffffffff8137468a
[
ffffc9003fcc3b08] generic_make_request at
ffffffff81368b49
[
ffffc9003fcc3b68] submit_bio at
ffffffff81368d7d
[
ffffc9003fcc3bb8] ext4_io_submit at
ffffffffa031be00 [ext4]
[
ffffc9003fcc3c00] ext4_writepages at
ffffffffa03163de [ext4]
[
ffffc9003fcc3d68] do_writepages at
ffffffff811c49ae
[
ffffc9003fcc3d78] __filemap_fdatawrite_range at
ffffffff811b6188
[
ffffc9003fcc3e30] filemap_write_and_wait_range at
ffffffff811b6301
[
ffffc9003fcc3e60] ext4_sync_file at
ffffffffa030cee8 [ext4]
[
ffffc9003fcc3ea8] vfs_fsync_range at
ffffffff8128594b
[
ffffc9003fcc3ee8] do_fsync at
ffffffff81285abd
[
ffffc9003fcc3f18] sys_fsync at
ffffffff81285d50
[
ffffc9003fcc3f28] do_syscall_64 at
ffffffff81003c04
[
ffffc9003fcc3f50] entry_SYSCALL_64_after_swapgs at
ffffffff81742b8e
The ->inflight counter may be negative (-1) if
1) blk-iolatency was disabled when the IO was issued,
2) blk-iolatency was enabled before this IO reached its endio,
3) the ->inflight counter is decreased from 0 to -1 in endio()
In fact the hang can be easily reproduced by the below script,
H=/sys/fs/cgroup/unified/
P=/sys/fs/cgroup/unified/test
echo "+io" > $H/cgroup.subtree_control
mkdir -p $P
echo $$ > $P/cgroup.procs
xfs_io -f -d -c "pwrite 0 4k" /dev/sdg
echo "`cat /sys/block/sdg/dev` target=
1000000" > $P/io.latency
xfs_io -f -d -c "pwrite 0 4k" /dev/sdg
This fixes the problem by freezing the queue so that while
enabling/disabling iolatency, there is no inflight rq running.
Note that quiesce_queue is not needed as this only updating iolatency
configuration about which dispatching request_queue doesn't care.
Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>