linux-kernel - Re: [NFS] [PATCH] NFSD: fix uninitialized variable

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Message-ID: <20070529195227.GG6815@fieldses.org>
Date:	Tue, 29 May 2007 15:52:27 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, neilb@...e.de,
	nfs@...ts.sourceforge.net, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [NFS] [PATCH] NFSD: fix uninitialized variable

On Mon, May 28, 2007 at 11:19:21PM -0400, Jeff Garzik wrote:
> J. Bruce Fields wrote:
> >But I don't want anyone else wasting their time on this.  Should we cave
> >in and add the initialization here just to shut up gcc?  Or would a
> >comment here help?
> 
> Given what you said above, I don't see gcc, on its best day, will ever 
> know enough to validate that that variable is indeed always initialized. 

I recall there being arguments before about when to add initializations.
Unfortunately I can't remember the content of those arguments.  But I
thought that on the gcc-haters side the complaint was exactly that gcc
was emitting warnings in cases where it could never hope to determine
whether an initialization is required.  Am I misremembering?

>  So I would vote for silencing it on those grounds.

That said, I'm OK with the extra initialization.  Might be worth a
comment, though, just to avoid giving the wrong impression about the
assumptions here; something like:

--b.

diff --git a/fs/nfsd/nfs4acl.c b/fs/nfsd/nfs4acl.c
index cc3b7ba..4adb5ee 100644
--- a/fs/nfsd/nfs4acl.c
+++ b/fs/nfsd/nfs4acl.c
@@ -183,8 +183,13 @@ static void
 summarize_posix_acl(struct posix_acl *acl, struct posix_acl_summary *pas)
 {
 	struct posix_acl_entry *pa, *pe;
-	pas->users = 0;
-	pas->groups = 0;
+
+	/*
+	 * Only pas.users and pas.groups need initialization; previous
+	 * posix_acl_valid() calls ensure that the other fields will be
+	 * initialized in the following loop.  But, just to placate gcc:
+	 */
+	memset(pas, 0, sizeof(*pas));
 	pas->mask = 07;
 
 	pe = acl->a_entries + acl->a_count;
-
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