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    Subject[PATCH] vfs: document locking requirements for d_move, __d_move and d_materialise_unique (try #2)
    Date
    Adding a comment to d_materialise_unique per Al's request...

    d_move and __d_move have some pretty substantial locking requirements,
    but they are not clearly documented. Add some comments spelling them
    out. Also, document the requirement for the i_mutex of the parent in
    d_materialise_unique.

    Cc: Al Viro <viro@ZenIV.linux.org.uk>
    Signed-off-by: Jeff Layton <jlayton@redhat.com>
    ---
    fs/dcache.c | 11 +++++++----
    1 files changed, 7 insertions(+), 4 deletions(-)

    diff --git a/fs/dcache.c b/fs/dcache.c
    index be18598..b05aac3 100644
    --- a/fs/dcache.c
    +++ b/fs/dcache.c
    @@ -2138,8 +2138,9 @@ static void dentry_unlock_parents_for_move(struct dentry *dentry,
    * @target: new dentry
    *
    * Update the dcache to reflect the move of a file name. Negative
    - * dcache entries should not be moved in this way. Caller hold
    - * rename_lock.
    + * dcache entries should not be moved in this way. Caller must hold
    + * rename_lock, the i_mutex of the source and target directories,
    + * and the sb->s_vfs_rename_mutex if they differ. See lock_rename().
    */
    static void __d_move(struct dentry * dentry, struct dentry * target)
    {
    @@ -2202,7 +2203,8 @@ static void __d_move(struct dentry * dentry, struct dentry * target)
    * @target: new dentry
    *
    * Update the dcache to reflect the move of a file name. Negative
    - * dcache entries should not be moved in this way.
    + * dcache entries should not be moved in this way. See the locking
    + * requirements for __d_move.
    */
    void d_move(struct dentry *dentry, struct dentry *target)
    {
    @@ -2320,7 +2322,8 @@ static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
    * @inode: inode to bind to the dentry, to which aliases may be attached
    *
    * Introduces an dentry into the tree, substituting an extant disconnected
    - * root directory alias in its place if there is one
    + * root directory alias in its place if there is one. Caller must hold the
    + * i_mutex of the parent directory.
    */
    struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode)
    {
    --
    1.7.1


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