linux-kernel - Re: VM: Fix nasty and subtle race in shared mmap'ed page writeback

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Date:	Wed, 3 Jan 2007 22:12:20 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Linus Torvalds <torvalds@...l.org>,
	Andrea Gelmini <gelma@...ma.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: VM: Fix nasty and subtle race in shared mmap'ed page writeback

On Thu, 04 Jan 2007 17:03:43 +1100
Nick Piggin <nickpiggin@...oo.com.au> wrote:

> > That bug was introduced in 2.6.19, with the dirty page tracking patches.
> > 
> > 2.6.18 and earlier used ->private_lock coverage in try_to_free_buffers() to
> > prevent it.
> 
> Ohh, right you are, I was looking at 2.6.19 sources. The comments above
> ttfb match that as well. Curious that the dirty page patches were allowed
> to mess with this...

Frankly, those patches scared the crap out of me, specifically because of
the delicacy and complexity of the various dirtiness state coherencies. 
But I just didn't have the bandwidth to go through them with a sufficiently
fine toothcomb, sorry.

> Anyway that leaves us with the question of why Andrea's database is getting
> corrupted. Hopefully he can give us a minimal test-case.

It'd odd that stories of pre-2.6.19 BerkeleyDB corruption are now coming
out of the woodwork.  It's the first I've ever heard of them.

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