linux-ext4 - RE: [PATCH 1/2] ext4: introduce new i_write

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Message-id: <000f01cf7fb9$f4c4cfd0$de4e6f70$@samsung.com>
Date:	Wed, 04 Jun 2014 14:58:06 +0900
From:	Namjae Jeon <namjae.jeon@...sung.com>
To:	'Theodore Ts'o' <tytso@....edu>
Cc:	'Lukáš Czerner' <lczerner@...hat.com>,
	'linux-ext4' <linux-ext4@...r.kernel.org>,
	'Ashish Sangwan' <a.sangwan@...sung.com>
Subject: RE: [PATCH 1/2] ext4: introduce new i_write_mutex to protect fallocate

> 
> On Tue, Jun 03, 2014 at 03:04:32PM +0900, Namjae Jeon wrote:
> > IMHO, If our goal is to solve the problem of xfstests, we can use only
> > "ext4: fix ZERO_RANGE test failure in data journalling" patch without
> > i_write_mutex patch. And we can add lock for fallocate on next kernel
> > after checking with sufficient time.
> 
> I thought this patch required i_write_mutex to avoid a race where
> another thread modifies an inode while filemap_write_and_wait_range()
> is running?
Yes, Right.
> 
> I agree that we could drop the i_write_mutex and add a call to
> ext4_force_commit() which should make the xfstest failure rarer, but
> the race would still be there, yes?
Yes, It is there but as Lukas said it is not critical than a possible
locking overhead. So, IMHO this is not something which needs urgent
attention and can be tackled properly after checking unclear
performance measurement on high-end server.

Thanks.
> 
> 						- Ted

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