linux-kernel - Re: [PATCH] fuse: hotfix truncate

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Message-ID: <CAJfpegvLcu1o+FUyRL1phCGMKvB4tReyjMLXBb6JabNJxooRSw@mail.gmail.com>
Date:	Thu, 29 Aug 2013 18:18:09 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Maxim Patlasov <mpatlasov@...allels.com>
Cc:	Pavel Emelianov <xemul@...allels.com>,
	fuse-devel <fuse-devel@...ts.sourceforge.net>,
	Brian Foster <bfoster@...hat.com>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	James Bottomley <jbottomley@...allels.com>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>, devel@...nvz.org
Subject: Re: [PATCH] fuse: hotfix truncate_pagecache() issue

On Thu, Aug 29, 2013 at 3:01 PM, Maxim Patlasov <mpatlasov@...allels.com> wrote:
> The patch looks fine, but it solves only one side of the problem (exactly
> what you formulated above). Another side is opposite: truncating page cache
> too late, when the state of inode changed significantly. The beginning may
> be as in the scenario above: fuse_dentry_revalidate() discovered that i_size
> changed (due to our own fuse_do_setattr()) and is going to call
> truncate_pagecache() for some 'new_size' it believes valid right now. But by
> the time that particular truncate_pagecache() is called, a lot of things may
> happen:
>
> 1) fuse_do_setattr() called truncate_pagecache() according to your patch
> 2) the file was extended either by write(2) or ftruncate(2) or fallocate(2).
> 3) mmap-ed write make a page in the extended region dirty
>
> The result will be the lost of data user wrote on the step '3)'. (my patch
> solves the issue at least for all cases w/o external changes)

I get it.

Could you please resend the patch with all these failure cases
described in the header?

Thanks,
Miklos
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