GIT: unionfs2-2.6.27.y: bugfixes: correctly decrement refcounts of mnt's upon branch management

[Erez Zadok]

commit cbd682cd4fa5cb861752b5d763ce5efeb876f709
Author: Erez_Zadok <ezk at cs.sunysb.edu>
Date:   Fri May 11 01:55:19 2007 -0400

    bugfixes: correctly decrement refcounts of mnt's upon branch management
    
    The old logic was broken in one place, which another place tried to "fix"
    incorrectly.  Also added detailed comments to explain the new/correct logic.

diff --git a/fs/unionfs/commonfops.c b/fs/unionfs/commonfops.c
index d4a14e4..2cbf561 100644
--- a/fs/unionfs/commonfops.c
+++ b/fs/unionfs/commonfops.c
@@ -134,14 +134,21 @@ static void cleanup_file(struct file *file)
 				       "file %p\n", file);
 			else {
 				unionfs_read_lock(sb);
+				/* decrement count of open files */
 				branchput(sb, i);
 				unionfs_read_unlock(sb);
-				/* XXX: is it OK to use sb->s_root here? */
-				unionfs_mntput(sb->s_root, i);
-				/* mntget b/c fput below will call mntput */
-				unionfs_mntget(sb->s_root, bindex);
+				/*
+				 * fput will perform an mntput for us on the
+				 * correct branch.  Although we're using the
+				 * file's old branch configuration, bindex,
+				 * which is the old index, correctly points
+				 * to the right branch in the file's branch
+				 * list.  In other words, we're going to
+				 * mntput the correct branch even if
+				 * branches have been added/removed.
+				 */
+				fput(unionfs_lower_file_idx(file, bindex));
 			}
-			fput(unionfs_lower_file_idx(file, bindex));
 		}
 	}
 
diff --git a/fs/unionfs/dentry.c b/fs/unionfs/dentry.c
index 7eac160..d1ee792 100644
--- a/fs/unionfs/dentry.c
+++ b/fs/unionfs/dentry.c
@@ -257,14 +257,22 @@ out_this:
 	/* finally, lock this dentry and revalidate it */
 	verify_locked(dentry);
 	dgen = atomic_read(&UNIONFS_D(dentry)->generation);
-	saved_bstart = dbstart(dentry);
-	saved_bend = dbend(dentry);
 	valid = __unionfs_d_revalidate_one(dentry, nd);
 
-	if (valid && chain_len > 0 && sbgen != dgen) {
-		for (bindex = saved_bstart; bindex <= saved_bend; bindex++)
+	/*
+	 * If __unionfs_d_revalidate_one() succeeded above, then it will
+	 * have incremented the refcnt of the mnt's, but also the branch
+	 * indices of the dentry will have been updated (to take into
+	 * account any branch insertions/deletion.  So the current
+	 * dbstart/dbend match the current, and new, indices of the mnts
+	 * which __unionfs_d_revalidate_one has incremented.  Note: the "if"
+	 * test below does not depend on whether chain_len was 0 or greater.
+	 */
+	if (valid && sbgen != dgen)
+		for (bindex = dbstart(dentry);
+		     bindex <= dbend(dentry);
+		     bindex++)
 			unionfs_mntput(dentry, bindex);
-	}
 
 out_free:
 	/* unlock/dput all dentries in chain and return status */