gfs2: Prevent inode creation race (2)

In gfs2_try_evict(), we try grabbing the inode to evict, we try to evict
it, and then we try grabbing it again to see if it still exists.  There
is no guarantee that we will end up with the same inode both times; the
inode validity check that commit ffd1cf0 ("gfs2: Prevent inode
creation race") added to the first grab is actually needed both times.

(To avoid code duplication, add a grab_existing_inode() helper.)

Signed-off-by: Andreas Gruenbacher <[email protected]>

Author: Andreas Gruenbacher

fs/gfs2/glock.c

@@ -971,6 +971,25 @@ static void gfs2_glock_poke(struct gfs2_glock *gl)
 	gfs2_holder_uninit(&gh);
 }
 
+static struct gfs2_inode *gfs2_grab_existing_inode(struct gfs2_glock *gl)
+{
+	struct gfs2_inode *ip;
+
+	spin_lock(&gl->gl_lockref.lock);
+	ip = gl->gl_object;
+	if (ip && !igrab(&ip->i_inode))
+		ip = NULL;
+	spin_unlock(&gl->gl_lockref.lock);
+	if (ip) {
+		wait_on_inode(&ip->i_inode);
+		if (is_bad_inode(&ip->i_inode)) {
+			iput(&ip->i_inode);
+			ip = NULL;
+		}
+	}
+	return ip;
+}
+
 static void gfs2_try_evict(struct gfs2_glock *gl)
 {
 	struct gfs2_inode *ip;
@@ -988,32 +1007,15 @@ static void gfs2_try_evict(struct gfs2_glock *gl)
 	 * happened below.  (Verification is triggered by the call to
 	 * gfs2_queue_verify_delete() in gfs2_evict_inode().)
 	 */
-	spin_lock(&gl->gl_lockref.lock);
-	ip = gl->gl_object;
-	if (ip && !igrab(&ip->i_inode))
-		ip = NULL;
-	spin_unlock(&gl->gl_lockref.lock);
-	if (ip) {
-		wait_on_inode(&ip->i_inode);
-		if (is_bad_inode(&ip->i_inode)) {
-			iput(&ip->i_inode);
-			ip = NULL;
-		}
-	}
+	ip = gfs2_grab_existing_inode(gl);
 	if (ip) {
 		set_bit(GLF_DEFER_DELETE, &gl->gl_flags);
 		d_prune_aliases(&ip->i_inode);
 		iput(&ip->i_inode);
 		clear_bit(GLF_DEFER_DELETE, &gl->gl_flags);
 
 		/* If the inode was evicted, gl->gl_object will now be NULL. */
-		spin_lock(&gl->gl_lockref.lock);
-		ip = gl->gl_object;
-		if (ip) {
-			if (!igrab(&ip->i_inode))
-				ip = NULL;
-		}
-		spin_unlock(&gl->gl_lockref.lock);
+		ip = gfs2_grab_existing_inode(gl);
 		if (ip) {
 			gfs2_glock_poke(ip->i_gl);
 			iput(&ip->i_inode);