linux-ext4 - Re: [PATCH][RFC]JBD2: Fix journal checksum kernel oops on NUMA

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Message-Id: <1194021108.1547.14.camel@dyn9047017100.beaverton.ibm.com>
Date:	Fri, 02 Nov 2007 08:31:48 -0800
From:	Badari Pulavarty <pbadari@...il.com>
To:	Andreas Dilger <adilger@....com>
Cc:	Mingming Cao <cmm@...ibm.com>,
	Girish Shilamkar <girish@...sterfs.com>,
	Avantika Mathur <mathur@...ux.vnet.ibm.com>,
	ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH][RFC]JBD2: Fix journal checksum kernel oops on NUMA

On Fri, 2007-11-02 at 13:20 +0800, Andreas Dilger wrote:
> On Nov 01, 2007  17:40 -0700, Mingming Cao wrote:
> > Current journal checksumming patch failed fsstress test on NUMA. The 
> > bh->b_data passed to the crc32_be () function could be NULL pointer, 
> > which caused kernel oops immediately when running fsstress with -o 
> > journal_checksum. It is because the page is part of highmem on NUMA box.
> > We need to kmap the page before access the bh->b_data to calculate
> > the checksums.
> 
> I have no objection to the patch, per-se, but I'm surprised that there
> would ever be a buffer head pointing at a page in high memory?  That
> seems contrary to what I would expect...

I was surprised to see that too while helping Mingming/Avantika track
this issue. I was under impression that we are checksumming only
metadata and it should be lowmem. But only "buffer_head"s are in lowmem.
Pages that point to can be in Highmem.

Thanks,
Badari

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