linux-kernel - Re: [PATCH -V2] hugetlbfs: Drop taking inode i_mutex lock from hugetlbfs

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Message-ID: <20120301224014.GA21990@redhat.com>
Date:	Thu, 1 Mar 2012 17:40:14 -0500
From:	Dave Jones <davej@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	linux-mm@...ck.org, mgorman@...e.de,
	kamezawa.hiroyu@...fujitsu.com, dhillf@...il.com,
	viro@...iv.linux.org.uk, hughd@...gle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -V2] hugetlbfs: Drop taking inode i_mutex lock from
 hugetlbfs_read

On Thu, Mar 01, 2012 at 02:10:07PM -0800, Andrew Morton wrote:
 
 > > AFAIU i_mutex lock got added to  hugetlbfs_read as per
 > > http://lkml.indiana.edu/hypermail/linux/kernel/0707.2/3066.html
 > > to take care of the race between truncate and read. This patch fix
 > > this by looking at page->mapping under page_lock (find_lock_page())
 > > to ensure; the inode didn't get truncated in the range during a
 > > parallel read.
 > > 
 > > Ideally we can extend the patch to make sure we don't increase i_size
 > > in mmap. But that will break userspace, because application will now
 > > have to use truncate(2) to increase i_size in hugetlbfs.
 > 
 > Looks OK to me.
 > 
 > Given that the bug has been there for four years, I'm assuming that
 > we'll be OK merging this fix into 3.4.  Or we could merge it into 3.4
 > and tag it for backporting into earlier kernels - it depends on whether
 > people are hurting from it, which I don't know?

My testing hits this every day. It's not a real problem, but it's annoying
to see the lockdep spew constantly.  We've had a couple Fedora users
report it too in regular day-to-day use as opposed to the hostile
workloads I use to provoke it.

FWIW, I'll probably throw it in the Fedora kernels, so if it ends up
in stable, it'll be one less patch to carry.

	Dave

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