From 773cd04ec1911abb33cf9538b65f55b76cad5d92 Mon Sep 17 00:00:00 2001 From: Omar Sandoval Date: Mon, 18 May 2015 02:16:26 -0700 Subject: [PATCH] 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 ("btrfs: allow mounting btrfs subvolumes with different ro/rw options") Reviewed-by: David Sterba Signed-off-by: Omar Sandoval Signed-off-by: Chris Mason --- fs/btrfs/super.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c index c761d8e068e8..93f2edf6b603 100644 --- a/fs/btrfs/super.c +++ b/fs/btrfs/super.c @@ -1209,7 +1209,9 @@ 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); -- 2.20.1