From mboxrd@z Thu Jan 1 00:00:00 1970 From: Li Zefan Subject: Re: [PATCH] Btrfs: setup blank root and fs_info for mount time Date: Mon, 22 Nov 2010 17:21:40 +0800 Message-ID: <4CEA3624.8050002@cn.fujitsu.com> References: <1290196755-19607-1-git-send-email-josef@redhat.com> <1290392498.2602.21.camel@perseus.themaw.net> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: Josef Bacik , linux-btrfs@vger.kernel.org To: Ian Kent Return-path: In-Reply-To: <1290392498.2602.21.camel@perseus.themaw.net> List-ID: > Have a look in fs/super.c:generic_shutdown_super(), called by > fs/super.c:kill_anon_super(), where the super method ->put_super() is > called, setting the super s_fs_info to NULL, before taking the sb_lock > and removing it from the list of supers. > > Here's my patch. > > btrfs - fix race between btrfs_get_sb() and umount > > From: Ian Kent > > When mounting a btrfs file system btrfs_test_super() may attempt to > use sb->s_fs_info, the btrfs root, of a super block that is going away > and that has had the btrfs root set to NULL in its ->put_super(). But > if the super block is going away it cannot be an existing super block > so we can return false in this case. I think your analysis is right. Actually I ran the test script (posted in an earlier email), and it still crashed without your supplementary patch. > > Signed-off-by: Ian Kent > --- > > fs/btrfs/super.c | 6 ++++++ > 1 files changed, 6 insertions(+), 0 deletions(-) > > > diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c > index 6b57da3..960b320 100644 > --- a/fs/btrfs/super.c > +++ b/fs/btrfs/super.c > @@ -565,6 +565,12 @@ static int btrfs_test_super(struct super_block *s, void *data) > struct btrfs_fs_devices *test_fs_devices = data->fs_info->fs_devices; > struct btrfs_root *root = btrfs_sb(s); > > + /* > + * If this super block is going away, return false as it > + * can't match as an existing super block. > + */ > + if (!atomic_read(&s->s_active)) > + return 0; > return root->fs_info->fs_devices == test_fs_devices; > } > >