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authorRoss Lagerwall <ross.lagerwall@citrix.com>2023-07-14 13:11:06 +0300
committerJens Axboe <axboe@kernel.dk>2023-07-14 22:44:24 +0300
commit70904263512a74a3b8941dd9e6e515ca6fc57821 (patch)
tree48834c1ca901685d381a2725618752413f4df4ed /block/blk-core.c
parent9f87fc4d72f52b26ac3e19df5e4584227fe6740c (diff)
downloadlinux-70904263512a74a3b8941dd9e6e515ca6fc57821.tar.xz
blk-mq: Fix stall due to recursive flush plug
We have seen rare IO stalls as follows: * blk_mq_plug_issue_direct() is entered with an mq_list containing two requests. * For the first request, it sets last == false and enters the driver's queue_rq callback. * The driver queue_rq callback indirectly calls schedule() which calls blk_flush_plug(). This may happen if the driver has the BLK_MQ_F_BLOCKING flag set and is allowed to sleep in ->queue_rq. * blk_flush_plug() handles the remaining request in the mq_list. mq_list is now empty. * The original call to queue_rq resumes (with last == false). * The loop in blk_mq_plug_issue_direct() terminates because there are no remaining requests in mq_list. The IO is now stalled because the last request submitted to the driver had last == false and there was no subsequent call to commit_rqs(). Fix this by returning early in blk_mq_flush_plug_list() if rq_count is 0 which it will be in the recursive case, rather than checking if the mq_list is empty. At the same time, adjust one of the callers to skip the mq_list empty check as it is not necessary. Fixes: dc5fc361d891 ("block: attempt direct issue of plug list") Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com> Reviewed-by: Bart Van Assche <bvanassche@acm.org> Link: https://lore.kernel.org/r/20230714101106.3635611-1-ross.lagerwall@citrix.com Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-core.c')
-rw-r--r--block/blk-core.c3
1 files changed, 1 insertions, 2 deletions
diff --git a/block/blk-core.c b/block/blk-core.c
index 99d8b9812b18..90de50082146 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1144,8 +1144,7 @@ void __blk_flush_plug(struct blk_plug *plug, bool from_schedule)
{
if (!list_empty(&plug->cb_list))
flush_plug_callbacks(plug, from_schedule);
- if (!rq_list_empty(plug->mq_list))
- blk_mq_flush_plug_list(plug, from_schedule);
+ blk_mq_flush_plug_list(plug, from_schedule);
/*
* Unconditionally flush out cached requests, even if the unplug
* event came from schedule. Since we know hold references to the