+ /*
+ * If the dentry is not DCACHED_REFERENCED, it is time
+ * to remove it from the dcache, provided the super block is
+ * NULL (which means we are trying to reclaim memory)
+ * or this dentry belongs to the same super block that
+ * we want to shrink.
+ */
+ /*
+ * If this dentry is for "my" filesystem, then I can prune it
+ * without taking the s_umount lock (I already hold it).
+ */
+ if (sb && dentry->d_sb == sb) {
+ prune_one_dentry(dentry);
+ continue;
+ }
+ /*
+ * ...otherwise we need to be sure this filesystem isn't being
+ * unmounted, otherwise we could race with
+ * generic_shutdown_super(), and end up holding a reference to
+ * an inode while the filesystem is unmounted.
+ * So we try to get s_umount, and make sure s_root isn't NULL.
+ * (Take a local copy of s_umount to avoid a use-after-free of
+ * `dentry').
+ */
+ s_umount = &dentry->d_sb->s_umount;
+ if (down_read_trylock(s_umount)) {
+ if (dentry->d_sb->s_root != NULL) {
+ prune_one_dentry(dentry);
+ up_read(s_umount);
+ continue;
+ }
+ up_read(s_umount);
+ }
+ spin_unlock(&dentry->d_lock);
+ /* Cannot remove the first dentry, and it isn't appropriate
+ * to move it to the head of the list, so give up, and try
+ * later
+ */
+ break;