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Date: Tue, 7 Apr 2015 22:34:00 -0700 From: Omar Sandoval <osandov@...ndov.com> To: Chris Mason <clm@...com>, Josef Bacik <jbacik@...com>, David Sterba <dsterba@...e.cz>, linux-btrfs@...r.kernel.org Cc: linux-kernel@...r.kernel.org, Omar Sandoval <osandov@...ndov.com> Subject: [PATCH 1/3] Btrfs: lock superblock before remounting for rw subvol Since commit 0723a0473fb4 ("btrfs: allow mounting btrfs subvolumes with different ro/rw options"), when mounting a subvolume read/write when another subvolume has previously been mounted read-only, we first do a remount. However, this should be done with the superblock locked, as per sync_filesystem(): /* * We need to be protected against the filesystem going from * r/o to r/w or vice versa. */ WARN_ON(!rwsem_is_locked(&sb->s_umount)); This WARN_ON can easily be hit with: mkfs.btrfs -f /dev/vdb mount /dev/vdb /mnt btrfs subvol create /mnt/vol1 btrfs subvol create /mnt/vol2 umount /mnt mount -oro,subvol=/vol1 /dev/vdb /mnt mount -orw,subvol=/vol2 /dev/vdb /mnt2 Fixes: 0723a0473fb4 Signed-off-by: Omar Sandoval <osandov@...ndov.com> --- fs/btrfs/super.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c index 05fef19..d38be09 100644 --- a/fs/btrfs/super.c +++ b/fs/btrfs/super.c @@ -1205,7 +1205,9 @@ static struct dentry *mount_subvol(const char *subvol_name, int flags, return ERR_CAST(mnt); } + down_write(&mnt->mnt_sb->s_umount); r = btrfs_remount(mnt->mnt_sb, &flags, NULL); + up_write(&mnt->mnt_sb->s_umount); if (r < 0) { /* FIXME: release vfsmount mnt ??*/ kfree(newargs); -- 2.3.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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