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Btrfs: lock superblock before remounting for rw subvol
Since commit0723a0473f
("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:0723a0473f
("btrfs: allow mounting btrfs subvolumes with different ro/rw options") Reviewed-by: David Sterba <dsterba@suse.cz> Signed-off-by: Omar Sandoval <osandov@osandov.com> Signed-off-by: Chris Mason <clm@fb.com>
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1 changed files with 2 additions and 0 deletions
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@ -1209,7 +1209,9 @@ static struct dentry *mount_subvol(const char *subvol_name, int flags,
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return ERR_CAST(mnt);
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}
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down_write(&mnt->mnt_sb->s_umount);
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r = btrfs_remount(mnt->mnt_sb, &flags, NULL);
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up_write(&mnt->mnt_sb->s_umount);
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if (r < 0) {
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/* FIXME: release vfsmount mnt ??*/
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kfree(newargs);
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