linux-kernel - Re: Regression introduced by bfcfaa77bdf0f775263e906015982a608df01c76 (vfs: use 'unsigned long' accesses for dcache name comparison and hashing)

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Message-ID: <20120322215952.GG6589@ZenIV.linux.org.uk>
Date:	Thu, 22 Mar 2012 21:59:52 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com
Subject: Re: Regression introduced by
 bfcfaa77bdf0f775263e906015982a608df01c76 (vfs: use 'unsigned long' accesses
 for dcache name comparison and hashing)

On Thu, Mar 22, 2012 at 02:54:37PM -0700, Linus Torvalds wrote:
> On Thu, Mar 22, 2012 at 2:41 PM, Konrad Rzeszutek Wilk
> <konrad.wilk@...cle.com> wrote:
> >
> > Works for me! Thanks for coming up with a patch so quickly. Please add
> >
> > Reported-and-Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> 
> Goodie. Al, I can commit it as yours, but I'd want a sign-off and a
> commit message for that. Otherwise I'll take credit..

Hmm...  How about

Fix full_name_hash() behaviour when length is a multiple of 8

We want it to match what hash_name() is doing, which means extra
multiply by 9 in this case...

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
diff --git a/fs/namei.c b/fs/namei.c
index 13e6a1f..7451d6f8 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1439,10 +1439,10 @@ unsigned int full_name_hash(const unsigned char *name, unsigned int len)
 
 	for (;;) {
 		a = *(unsigned long *)name;
-		hash *= 9;
 		if (len < sizeof(unsigned long))
 			break;
 		hash += a;
+		hash *= 9;
 		name += sizeof(unsigned long);
 		len -= sizeof(unsigned long);
 		if (!len)
--
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