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    Subject[PATCH 3.10 49/80] Btrfs: send, dont BUG_ON() when an empty symlink is found
    Date
    3.10-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Filipe Manana <fdmanana@suse.com>

    commit a879719b8c90e15c9e7fa7266d5e3c0ca962f9df upstream.

    When a symlink is successfully created it always has an inline extent
    containing the source path. However if an error happens when creating
    the symlink, we can leave in the subvolume's tree a symlink inode without
    any such inline extent item - this happens if after btrfs_symlink() calls
    btrfs_end_transaction() and before it calls the inode eviction handler
    (through the final iput() call), the transaction gets committed and a
    crash happens before the eviction handler gets called, or if a snapshot
    of the subvolume is made before the eviction handler gets called. Sadly
    we can't just avoid this by making btrfs_symlink() call
    btrfs_end_transaction() after it calls the eviction handler, because the
    later can commit the current transaction before it removes any items from
    the subvolume tree (if it encounters ENOSPC errors while reserving space
    for removing all the items).

    So make send fail more gracefully, with an -EIO error, and print a
    message to dmesg/syslog informing that there's an empty symlink inode,
    so that the user can delete the empty symlink or do something else
    about it.

    Reported-by: Stephen R. van den Berg <srb@cuci.nl>
    Signed-off-by: Filipe Manana <fdmanana@suse.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/btrfs/send.c | 16 +++++++++++++++-
    1 file changed, 15 insertions(+), 1 deletion(-)

    --- a/fs/btrfs/send.c
    +++ b/fs/btrfs/send.c
    @@ -1338,7 +1338,21 @@ static int read_symlink(struct send_ctx
    ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
    if (ret < 0)
    goto out;
    - BUG_ON(ret);
    + if (ret) {
    + /*
    + * An empty symlink inode. Can happen in rare error paths when
    + * creating a symlink (transaction committed before the inode
    + * eviction handler removed the symlink inode items and a crash
    + * happened in between or the subvol was snapshoted in between).
    + * Print an informative message to dmesg/syslog so that the user
    + * can delete the symlink.
    + */
    + btrfs_err(root->fs_info,
    + "Found empty symlink inode %llu at root %llu",
    + ino, root->root_key.objectid);
    + ret = -EIO;
    + goto out;
    + }

    ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
    struct btrfs_file_extent_item);

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