linux-kernel - [PATCH 4.14 067/115] btrfs: Fix flush bio leak

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Message-Id: <20180302084506.576080973@linuxfoundation.org>
Date:   Fri,  2 Mar 2018 09:51:10 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Nikolay Borisov <nborisov@...e.com>,
        Liu Bo <bo.li.liu@...cle.com>, David Sterba <dsterba@...e.com>,
        Sasha Levin <alexander.levin@...izon.com>
Subject: [PATCH 4.14 067/115] btrfs: Fix flush bio leak

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nikolay Borisov <nborisov@...e.com>

[ Upstream commit beed9263f4000c48a5c48912f26576f6fa091181 ]

Commit e0ae99941423 ("btrfs: preallocate device flush bio") reworked
the way the flush bio is allocated and used. Concretely it allocates
the bio in __alloc_device and then re-uses it multiple times with a
very simple endio routine that just calls complete() without consuming
a reference. Allocated bios by default come with a ref count of 1,
which is then consumed by the endio routine (or not, in which case they
should be bio_put by the caller). The way the impleementation works now
is that the flush bio has a refcount of 2 and we only ever bio_put it
once, leaving it to hang indefinitely. Fix this by removing the extra
bio_get in __alloc_device.

Fixes: e0ae99941423 ("btrfs: preallocate device flush bio")
Signed-off-by: Nikolay Borisov <nborisov@...e.com>
Reviewed-by: Liu Bo <bo.li.liu@...cle.com>
Reviewed-by: David Sterba <dsterba@...e.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/btrfs/volumes.c |    1 -
 1 file changed, 1 deletion(-)

--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -236,7 +236,6 @@ static struct btrfs_device *__alloc_devi
 		kfree(dev);
 		return ERR_PTR(-ENOMEM);
 	}
-	bio_get(dev->flush_bio);

 	INIT_LIST_HEAD(&dev->dev_list);
 	INIT_LIST_HEAD(&dev->dev_alloc_list);