[patch 01/10] fs: fix do_lookup false negative

[Nick Piggin <npiggin@kernel.dk>]

[-- Attachment #1: fs-do_lookup-false-neg.patch --]
[-- Type: text/plain, Size: 1672 bytes --]

fs: fix do_lookup false negative

In do_lookup, if we initially find no dentry, we take the directory i_mutex and
re-check the lookup. If we find a dentry there, then we revalidate it if
needed. However if that revalidate asks for the dentry to be invalidated, we
return -ENOENT from do_lookup. What should happen instead is an attempt to
allocate and lookup a new dentry.

This is probably not noticed because it is rare. It is only reached if a
concurrent create races in first (in which case, the dentry probably won't be
invalidated anyway), or if the racy __d_lookup has failed due to a
false-negative (which is very rare).

Fix this by removing code and have it use the normal reval path.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>

---
 fs/namei.c |   10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

Index: linux-2.6/fs/namei.c
===================================================================
--- linux-2.6.orig/fs/namei.c	2010-08-18 04:04:18.000000000 +1000
+++ linux-2.6/fs/namei.c	2010-08-18 04:05:15.000000000 +1000
@@ -709,6 +709,7 @@ static int do_lookup(struct nameidata *n
 	dentry = __d_lookup(nd->path.dentry, name);
 	if (!dentry)
 		goto need_lookup;
+found:
 	if (dentry->d_op && dentry->d_op->d_revalidate)
 		goto need_revalidate;
 done:
@@ -766,14 +767,7 @@ out_unlock:
 	 * we waited on the semaphore. Need to revalidate.
 	 */
 	mutex_unlock(&dir->i_mutex);
-	if (dentry->d_op && dentry->d_op->d_revalidate) {
-		dentry = do_revalidate(dentry, nd);
-		if (!dentry)
-			dentry = ERR_PTR(-ENOENT);
-	}
-	if (IS_ERR(dentry))
-		goto fail;
-	goto done;
+	goto found;
 
 need_revalidate:
 	dentry = do_revalidate(dentry, nd);