fsnotify: fix unlink performance regression

__fsnotify_parent() has an optimization in place to avoid unneeded
take_dentry_name_snapshot().  When fsnotify_nameremove() was changed
not to call __fsnotify_parent(), we left out the optimization.
Kernel test robot reported a 5% performance regression in concurrent
unlink() workload.

Reported-by: kernel test robot <rong.a.chen@intel.com>
Link: https://lore.kernel.org/lkml/20190505062153.GG29809@shao2-debian/
Link: https://lore.kernel.org/linux-fsdevel/20190104090357.GD22409@quack2.suse.cz/
Fixes: 5f02a8776384 ("fsnotify: annotate directory entry modification events")
CC: stable@vger.kernel.org
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 41 insertions, 0 deletions

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index df06f3da166c..e8d3f349b7f2 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -108,6 +108,47 @@ void fsnotify_sb_delete(struct super_block *sb)
 }
 
 /*
+ * fsnotify_nameremove - a filename was removed from a directory
+ *
+ * This is mostly called under parent vfs inode lock so name and
+ * dentry->d_parent should be stable. However there are some corner cases where
+ * inode lock is not held. So to be on the safe side and be reselient to future
+ * callers and out of tree users of d_delete(), we do not assume that d_parent
+ * and d_name are stable and we use dget_parent() and
+ * take_dentry_name_snapshot() to grab stable references.
+ */
+void fsnotify_nameremove(struct dentry *dentry, int isdir)
+{
+        struct dentry *parent;
+        struct name_snapshot name;
+        __u32 mask = FS_DELETE;
+
+        /* d_delete() of pseudo inode? (e.g. __ns_get_path() playing tricks) */
+        if (IS_ROOT(dentry))
+                return;
+
+        if (isdir)
+                mask |= FS_ISDIR;
+
+        parent = dget_parent(dentry);
+        /* Avoid unneeded take_dentry_name_snapshot() */
+        if (!(d_inode(parent)->i_fsnotify_mask & FS_DELETE) &&
+            !(dentry->d_sb->s_fsnotify_mask & FS_DELETE))
+                goto out_dput;
+
+        take_dentry_name_snapshot(&name, dentry);
+
+        fsnotify(d_inode(parent), mask, d_inode(dentry), FSNOTIFY_EVENT_INODE,
+                 name.name, 0);
+
+        release_dentry_name_snapshot(&name);
+
+out_dput:
+        dput(parent);
+}
+EXPORT_SYMBOL(fsnotify_nameremove);
+
+/*
  * Given an inode, first check if we care what happens to our children.  Inotify
  * and dnotify both tell their parents about events.  If we care about any event
  * on a child we run all of our children and set a dentry flag saying that the