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block: destroy bdi before blockdev is unregistered.

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Because of the peculiar way that md devices are created (automatically
when the device node is opened), a new device can be created and
registered immediately after the
	blk_unregister_region(disk_devt(disk), disk->minors);
call in del_gendisk().

Therefore it is important that all visible artifacts of the previous
device are removed before this call.  In particular, the 'bdi'.

Since:
commit c4db59d31e
Author: Christoph Hellwig <hch@lst.de>
    fs: don't reassign dirty inodes to default_backing_dev_info

moved the
   device_unregister(bdi->dev);
call from bdi_unregister() to bdi_destroy() it has been quite easy to
lose a race and have a new (e.g.) "md127" be created after the
blk_unregister_region() call and before bdi_destroy() is ultimately
called by the final 'put_disk', which must come after del_gendisk().

The new device finds that the bdi name is already registered in sysfs
and complains

> [ 9627.630029] WARNING: CPU: 18 PID: 3330 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x5a/0x70()
> [ 9627.630032] sysfs: cannot create duplicate filename '/devices/virtual/bdi/9:127'

We can fix this by moving the bdi_destroy() call out of
blk_release_queue() (which can happen very late when a refcount
reaches zero) and into blk_cleanup_queue() - which happens exactly when the md
device driver calls it.

Then it is only necessary for md to call blk_cleanup_queue() before
del_gendisk().  As loop.c devices are also created on demand by
opening the device node, we make the same change there.

Fixes: c4db59d31e
Reported-by: Azat Khuzhin <a3at.mail@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org (v4.0)
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
NeilBrown 2015-04-27 14:12:22 +10:00 committed by Jens Axboe
parent 393a339705
commit 6cd18e711d
4 changed files with 5 additions and 5 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
block/blk-core.c
View file

@ -552,6 +552,8 @@ void blk_cleanup_queue(struct request_queue *q)
q->queue_lock = &q->__queue_lock;
spin_unlock_irq(lock);
bdi_destroy(&q->backing_dev_info);
/* @q is and will stay empty, shutdown and put */
blk_put_queue(q);
}

2
block/blk-sysfs.c
View file

@ -522,8 +522,6 @@ static void blk_release_queue(struct kobject *kobj)
blk_trace_shutdown(q);
bdi_destroy(&q->backing_dev_info);
ida_simple_remove(&blk_queue_ida, q->id);
call_rcu(&q->rcu_head, blk_free_queue_rcu);
}

2
drivers/block/loop.c
View file

@ -1620,8 +1620,8 @@ static int loop_add(struct loop_device **l, int i)
static void loop_remove(struct loop_device *lo)
{
del_gendisk(lo->lo_disk);
blk_cleanup_queue(lo->lo_queue);
del_gendisk(lo->lo_disk);
blk_mq_free_tag_set(&lo->tag_set);
put_disk(lo->lo_disk);
kfree(lo);

4
drivers/md/md.c
View file

@ -4754,12 +4754,12 @@ static void md_free(struct kobject *ko)
if (mddev->sysfs_state)
sysfs_put(mddev->sysfs_state);
if (mddev->queue)
blk_cleanup_queue(mddev->queue);
if (mddev->gendisk) {
del_gendisk(mddev->gendisk);
put_disk(mddev->gendisk);
}
if (mddev->queue)
blk_cleanup_queue(mddev->queue);
kfree(mddev);
}