linux-kernel - Re: [xfs-masters] Re: filesystem corruption on xfs after 2.6.25-rc1 (bisected, powerpc related?)

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Message-ID: <47C47127.7040700@sandeen.net>
Date:	Tue, 26 Feb 2008 12:05:59 -0800
From:	Eric Sandeen <sandeen@...deen.net>
To:	xfs-masters@....sgi.com
CC:	"Rafael J. Wysocki" <rjw@...k.pl>, Christoph Hellwig <hch@....de>,
	xfs@....sgi.com, johannes@...solutions.net,
	linux-kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [xfs-masters] Re: filesystem corruption on xfs after	2.6.25-rc1
 (bisected, powerpc related?)

Gaudenz Steinlin wrote:
> On Tue, Feb 26, 2008 at 01:13:56AM +0100, Rafael J. Wysocki wrote:
>> On Tuesday, 26 of February 2008, Christoph Hellwig wrote:
>>> On Tue, Feb 26, 2008 at 12:52:56AM +0100, Rafael J. Wysocki wrote:
>>>>> I'm not suggesting a partial revert; I just wonder which part of the
>>>>> change is causing the problem, as part of the debugging process.
> 
> I debuged this a bit further by testing the 4 changed functions
> individually. The problem only occurs with the new version of
> xfs_lowbit64. 

FWIW, Dave & I did some testing/debugging on 32-bit powerpc, and it is
indeed only xfs_lowbit64 which is doing the wrong thing on that arch,
because generic find_next_bit is doing the wrong thing on big-endian
32-bit systems, for sizes > 32 bits, near as I can tell.

Rather than reverting it all, I think just changing xfs_lowbit64 back to:

int
xfs_lowbit64(
       __uint64_t      v)
{
       __uint32_t      w = (__uint32_t)v;
       int             n = 0;

       if (w) {        /* lower bits */
               n = ffs(w);
       } else {        /* upper bits */
               w = (__uint32_t)(v >> 32);
               if (w && (n = ffs(w)))
                       n += 32;
       }
       return n - 1;
}

for now should fix it (this is essentially just ffs64())

-Eric
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