[PATCH 0/2] blk-mq: fix dispatch waiter accounting for reserved tags

[huhai <15815827059@163.com>]

From: Henry Hu <huhai@kylinos.cn>

blk_mq_mark_tag_wait() may queue hctx->dispatch_wait on breserved_tags
and increment that queue's ws_active. The wakeup path always decrements
bitmap_tags.ws_active, though. So the reserved counter stays elevated
and the regular counter can be decremented without a matching
increment, which may cause later wakeups to be skipped.

This is reachable and commit 98b99e9412d0 made the waiter side pick the
right queue but left the wakeup side hardcoded to bitmap_tags.

Henry Hu (2):
  sbitmap: add __sbitmap_add_wait_queue()
  blk-mq: fix dispatch waiter accounting for reserved tags

 block/blk-mq.c          | 33 +++++++++++++--------------------
 include/linux/blk-mq.h  |  2 +-
 include/linux/sbitmap.h |  9 ++++++++-
 lib/sbitmap.c           | 23 +++++++++++++++++++----
 4 files changed, 41 insertions(+), 26 deletions(-)


base-commit: 3f2425f5b5bbbdd991ca9cdfd5502e68d8895998
-- 
2.40.1