From: David Jeffery <djeffery@redhat.com>
Date: Mon, 28 Aug 2017 10:52:44 -0600
Subject: block: fix warning when I/O elevator is changed as request_queue is
being removed
Git-commit: e9a823fb34a8b0fcba6e112aa1003258a1a5af50
Patch-mainline: v4.14-rc1
References: bsc#1109979
There is a race between changing I/O elevator and request_queue removal
which can trigger the warning in kobject_add_internal. A program can
use sysfs to request a change of elevator at the same time another task
is unregistering the request_queue the elevator would be attached to.
The elevator's kobject will then attempt to be connected to the
request_queue in the object tree when the request_queue has just been
removed from sysfs. This triggers the warning in kobject_add_internal
as the request_queue no longer has a sysfs directory:
kobject_add_internal failed for iosched (error: -2 parent: queue)
------------[ cut here ]------------
WARNING: CPU: 3 PID: 14075 at lib/kobject.c:244 kobject_add_internal+0x103/0x2d0
To fix this warning, we can check the QUEUE_FLAG_REGISTERED flag when
changing the elevator and use the request_queue's sysfs_lock to
serialize between clearing the flag and the elevator testing the flag.
Signed-off-by: David Jeffery <djeffery@redhat.com>
Tested-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Johannes Thumshirn <jthumshirn@suse.de>
---
block/blk-sysfs.c | 2 ++
block/elevator.c | 4 ++++
2 files changed, 6 insertions(+)
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 27aceab1cc31..b8362c0df51d 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -931,7 +931,9 @@ void blk_unregister_queue(struct gendisk *disk)
if (WARN_ON(!q))
return;
+ mutex_lock(&q->sysfs_lock);
queue_flag_clear_unlocked(QUEUE_FLAG_REGISTERED, q);
+ mutex_unlock(&q->sysfs_lock);
wbt_exit(q);
diff --git a/block/elevator.c b/block/elevator.c
index 4bb2f0c93fa6..153926a90901 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -1055,6 +1055,10 @@ static int __elevator_change(struct request_queue *q, const char *name)
char elevator_name[ELV_NAME_MAX];
struct elevator_type *e;
+ /* Make sure queue is not in the middle of being removed */
+ if (!test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags))
+ return -ENOENT;
+
/*
* Special case for mq, turn off scheduling
*/