From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Mason <clm@fb.com>
Subject: Re: btrfs regression since 4.X kernel NULL pointer dereference
Date: Tue, 25 Aug 2015 09:51:46 -0400
Message-ID: <20150825135146.GE7176@ret.masoncoding.com>
References: <55D8B193.8010906@profihost.ag>
 <20150825090030.GF31630@lst.de>
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Cc: Stefan Priebe <s.priebe@profihost.ag>,
	"linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>,
	<linux-fsdevel@vger.kernel.org>
To: Christoph Hellwig <hch@lst.de>
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On Tue, Aug 25, 2015 at 11:00:30AM +0200, Christoph Hellwig wrote:
> I think this is btrfs using a struct block_device that doesn't have
> a valid queue pointer in it's gendisk for ->s_bdev.  And there are
> some fishy looking ->s_bdev assignments in the code which I suspect
> are related to it:
> 
> fs/btrfs/dev-replace.c: if (fs_info->sb->s_bdev == src_device->bdev)
> fs/btrfs/dev-replace.c:         fs_info->sb->s_bdev = tgt_device->bdev;
> fs/btrfs/volumes.c:     if (device->bdev == root->fs_info->sb->s_bdev)
> fs/btrfs/volumes.c:             root->fs_info->sb->s_bdev = next_device->bdev;
> fs/btrfs/volumes.c:     if (tgtdev->bdev == fs_info->sb->s_bdev)
> fs/btrfs/volumes.c:             fs_info->sb->s_bdev = next_device->bdev;

We've had trouble with this in the past, I'll take a look.

-chris