linux-kernel - [RFC 3/3] block: avoid deferral of blk_release

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Message-Id: <20200402000002.7442-4-mcgrof@kernel.org>
Date:   Thu,  2 Apr 2020 00:00:02 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     axboe@...nel.dk, viro@...iv.linux.org.uk,
        gregkh@...uxfoundation.org, rostedt@...dmis.org, mingo@...hat.com,
        jack@...e.cz, ming.lei@...hat.com, nstange@...e.de
Cc:     mhocko@...e.com, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Luis Chamberlain <mcgrof@...nel.org>,
        Bart Van Assche <bvanassche@....org>,
        Omar Sandoval <osandov@...com>,
        Hannes Reinecke <hare@...e.com>,
        Michal Hocko <mhocko@...nel.org>
Subject: [RFC 3/3] block: avoid deferral of blk_release_queue() work

Commit dc9edc44de6c ("block: Fix a blk_exit_rl() regression") moved
the blk_release_queue() into a workqueue after a splat floated around
with some work here which could sleep in blk_exit_rl().

On recent commit db6d9952356 ("block: remove request_list code") though
Jens Axboe removed this code, now merged since v5.0. We no longer have
to defer this work.

By doing this we also avoid failing to detach / attach a block
device with a BLKTRACESETUP. This issue can be reproduced with
break-blktrace [0] using:

  break-blktrace -c 10 -d -s

The kernel does not crash without this commit, it just fails to
create the block device because the prior block device removal
deferred work is pending. After this commit we can use the above
flaky use of blktrace without an issue.

[0] https://github.com/mcgrof/break-blktrace

Cc: Bart Van Assche <bvanassche@....org>
Cc: Omar Sandoval <osandov@...com>
Cc: Hannes Reinecke <hare@...e.com>
Cc: Nicolai Stange <nstange@...e.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Michal Hocko <mhocko@...nel.org>
Suggested-by: Nicolai Stange <nstange@...e.de>
Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
---
 block/blk-sysfs.c | 18 +++++-------------
 1 file changed, 5 insertions(+), 13 deletions(-)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 20f20b0fa0b9..f159b40899ee 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -862,8 +862,8 @@ static void blk_exit_queue(struct request_queue *q)
 
 
 /**
- * __blk_release_queue - release a request queue
- * @work: pointer to the release_work member of the request queue to be released
+ * blk_release_queue - release a request queue
+ * @kojb: pointer to the kobj representing the request queue
  *
  * Description:
  *     This function is called when a block device is being unregistered. The
@@ -873,9 +873,10 @@ static void blk_exit_queue(struct request_queue *q)
  *     of the request queue reaches zero, blk_release_queue is called to release
  *     all allocated resources of the request queue.
  */
-static void __blk_release_queue(struct work_struct *work)
+static void blk_release_queue(struct kobject *kobj)
 {
-	struct request_queue *q = container_of(work, typeof(*q), release_work);
+	struct request_queue *q =
+		container_of(kobj, struct request_queue, kobj);
 
 	if (test_bit(QUEUE_FLAG_POLL_STATS, &q->queue_flags))
 		blk_stat_remove_callback(q, q->poll_cb);
@@ -905,15 +906,6 @@ static void __blk_release_queue(struct work_struct *work)
 	call_rcu(&q->rcu_head, blk_free_queue_rcu);
 }
 
-static void blk_release_queue(struct kobject *kobj)
-{
-	struct request_queue *q =
-		container_of(kobj, struct request_queue, kobj);
-
-	INIT_WORK(&q->release_work, __blk_release_queue);
-	schedule_work(&q->release_work);
-}
-
 static const struct sysfs_ops queue_sysfs_ops = {
 	.show	= queue_attr_show,
 	.store	= queue_attr_store,
-- 
2.25.1