On Wed, Aug 18, 2010 at 04:37:30AM +1000, Nick Piggin wrote:
> 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@xxxxxxxxx>
>
> ---
> 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);
>
>
Looks good.
Reviewed-by: Valerie Aurora <vaurora@xxxxxxxxxx>
-VAL
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