tree bbe47f1b91edbae94b582649b7d11a4b2b2fb877
parent f66227de5924ed0fde1823f5cbc4d8b8f45faaa2
author Omar Sandoval <osandov@fb.com> 1484769322 -0800
committer Jens Axboe <axboe@fb.com> 1484772115 -0700

sbitmap: fix wakeup hang after sbq resize

When we resize a struct sbitmap_queue, we update the wakeup batch size,
but we don't update the wait count in the struct sbq_wait_states. If we
resized down from a size which could use a bigger batch size, these
counts could be too large and cause us to miss necessary wakeups. To fix
this, update the wait counts when we resize (ensuring some careful
memory ordering so that it's safe w.r.t. concurrent clears).

This also fixes a theoretical issue where two threads could end up
bumping the wait count up by the batch size, which could also
potentially lead to hangs.

Reported-by: Martin Raiber <martin@urbackup.org>
Fixes: e3a2b3f931f5 ("blk-mq: allow changing of queue depth through sysfs")
Fixes: 2971c35f3588 ("blk-mq: bitmap tag: fix race on blk_mq_bitmap_tags::wake_cnt")
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>