Date:	Fri, 15 May 2015 16:03:23 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	gregkh@...uxfoundation.org
Cc:	neilb@...e.de, a3at.mail@...il.com, axboe@...com, hch@....de,
	stable@...r.kernel.org, stable-commits@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Patch "block: destroy bdi before blockdev is unregistered." has
 been added to the 4.0-stable tree

On (05/14/15 19:18), gregkh@...uxfoundation.org wrote:
> This is a note to let you know that I've just added the patch titled
> 
>     block: destroy bdi before blockdev is unregistered.
> 
> to the 4.0-stable tree which can be found at:
>     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> 
> The filename of the patch is:
>      block-destroy-bdi-before-blockdev-is-unregistered.patch
> and it can be found in the queue-4.0 subdirectory.
> 
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@...r.kernel.org> know about it.
> 
> 

Hello Greg,

jfi, I think this commit will WARN_ON(). fixed by https://lkml.org/lkml/2015/5/8/29


(https://lkml.org/lkml/2015/4/28/568)

	-ss

> From 6cd18e711dd8075da9d78cfc1239f912ff28968a Mon Sep 17 00:00:00 2001
> From: NeilBrown <neilb@...e.de>
> Date: Mon, 27 Apr 2015 14:12:22 +1000
> Subject: block: destroy bdi before blockdev is unregistered.
> 
> From: NeilBrown <neilb@...e.de>
> 
> commit 6cd18e711dd8075da9d78cfc1239f912ff28968a upstream.
> 
> 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 c4db59d31e39ea067c32163ac961e9c80198fd37
> Author: Christoph Hellwig <hch@....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: c4db59d31e39ea067c32163ac961e9c80198fd37
> Reported-by: Azat Khuzhin <a3at.mail@...il.com>
> Cc: Christoph Hellwig <hch@....de>
> Signed-off-by: NeilBrown <neilb@...e.de>
> Reviewed-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Jens Axboe <axboe@...com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> 
> ---
>  block/blk-core.c     |    2 ++
>  block/blk-sysfs.c    |    2 --
>  drivers/block/loop.c |    2 +-
>  drivers/md/md.c      |    4 ++--
>  4 files changed, 5 insertions(+), 5 deletions(-)
> 
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -552,6 +552,8 @@ void blk_cleanup_queue(struct request_qu
>  		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);
>  }
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -522,8 +522,6 @@ static void blk_release_queue(struct kob
>  
>  	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);
>  }
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1672,8 +1672,8 @@ out:
>  
>  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);
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -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);
>  }
> 
> 
> Patches currently in stable-queue which might be from neilb@...e.de are
> 
> queue-4.0/block-destroy-bdi-before-blockdev-is-unregistered.patch
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