On Fri, Sep 4, 2009 at 2:51 AM, <npiggin@xxxxxxx> wrote:
> Make d_count non-atomic and protect it with d_lock. This allows us to
> ensure a 0 refcount dentry remains 0 without dcache_lock. It is also
> fairly natural when we start protecting many other dentry members with
> d_lock.
> +struct dentry *dget_parent(struct dentry *dentry)
> +{
> + struct dentry *ret;
> +
> +repeat:
> + spin_lock(&dentry->d_lock);
> + ret = dentry->d_parent;
> + if (!ret)
> + goto out;
> + if (!spin_trylock(&ret->d_lock)) {
> + spin_unlock(&dentry->d_lock);
> + goto repeat;
> + }
> + BUG_ON(!ret->d_count);
> + ret->d_count++;
> + spin_unlock(&ret->d_lock);
> +out:
> + spin_unlock(&dentry->d_lock);
> + return ret;
> +}
> +EXPORT_SYMBOL(dget_parent);
> Index: linux-2.6/fs/notify/inotify/inotify.c
> ===================================================================
> --- linux-2.6.orig/fs/notify/inotify/inotify.c
> +++ linux-2.6/fs/notify/inotify/inotify.c
> @@ -339,18 +339,26 @@ void inotify_dentry_parent_queue_event(s
> if (!(dentry->d_flags & DCACHE_INOTIFY_PARENT_WATCHED))
> return;
>
> +again:
> spin_lock(&dentry->d_lock);
> parent = dentry->d_parent;
> + if (!spin_trylock(&parent->d_lock)) {
> + spin_unlock(&dentry->d_lock);
> + goto again;
> + }
> inode = parent->d_inode;
>
> if (inotify_inode_watched(inode)) {
> - dget(parent);
> + dget_dlock(parent);
> spin_unlock(&dentry->d_lock);
> + spin_unlock(&parent->d_lock);
> inotify_inode_queue_event(inode, mask, cookie, name,
> dentry->d_inode);
> dput(parent);
> - } else
> + } else {
> spin_unlock(&dentry->d_lock);
> + spin_unlock(&parent->d_lock);
> + }
I don't think I understand why in both of these cases you don't need
to check for dentry->d_parent == dentry
> Index: linux-2.6/fs/notify/fsnotify.c
> ===================================================================
> --- linux-2.6.orig/fs/notify/fsnotify.c
> +++ linux-2.6/fs/notify/fsnotify.c
> @@ -87,13 +87,18 @@ void __fsnotify_parent(struct dentry *de
> if (!(dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED))
> return;
>
> +again:
> spin_lock(&dentry->d_lock);
> parent = dentry->d_parent;
> + if (parent != dentry && !spin_trylock(&parent->d_lock)) {
> + spin_unlock(&dentry->d_lock);
> + goto again;
> + }
> p_inode = parent->d_inode;
>
> if (fsnotify_inode_watches_children(p_inode)) {
> if (p_inode->i_fsnotify_mask & mask) {
> - dget(parent);
> + dget_dlock(parent);
> send = true;
> }
> } else {
And yet in this case we do check for dentry->d_parent == dentry. (my
unknowing self thinks we'd want to check in all places)
-Eric
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