linux-kernel - Re: [PATCH] hugetlbfs read() support

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Message-ID: <46A05270.5040205@yahoo.com.au>
Date:	Fri, 20 Jul 2007 16:13:04 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Badari Pulavarty <pbadari@...ibm.com>,
	Bill Irwin <bill.irwin@...cle.com>, nacc@...ibm.com,
	lkml <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH] hugetlbfs read() support

(sorry if this is a resend... something bad seems to have happened to me)

Andrew Morton wrote:
> On Thu, 19 Jul 2007 08:51:49 -0700 Badari Pulavarty <pbadari@...ibm.com> wrote:

>>>This code doesn't have all the ghastly tricks which we deploy to handle
>>>concurrent truncate.
>>
>>Do I need to ? Baaahh!!  I don't want to deal with them. 
> 
> 
> Nick, can you think of any serious consequences of a read/truncate race in
> there?  I can't..

As it doesn't allow writes, then I _think_ it should be OK. If you
ever did want to add write(2) support, then you would have transient
zeroes problems.

But I'm not completely sure.. we've had a lot of (and still have
some known and probably unknown) bugs just in that single
generic_mapping_read function, most of which are due to our rabid
aversion to doing any locking whatsoever there.

So why not just hold i_mutex around the whole thing to be safe?

-- 
SUSE Labs, Novell Inc.
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