linux-kernel - Re: [PULL REQUEST] : ima-appraisal patches

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Date:	Wed, 18 Apr 2012 14:07:52 -0400
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	James Morris <jmorris@...ei.org>
Cc:	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Al Viro <viro@...IV.linux.org.uk>,
	David Safford <safford@...ux.vnet.ibm.com>,
	Dmitry Kasatkin <dmitry.kasatkin@...el.com>
Subject: Re: [PULL REQUEST] : ima-appraisal patches

On Thu, 2012-04-19 at 01:02 +1000, James Morris wrote:
> On Wed, 18 Apr 2012, Mimi Zohar wrote:
> 
> > Hi James,
> > 
> > As the last IMA-appraisal posting on 3/29 addressed Al's
> > performance/maintenance concerns of deferring the __fput() and there
> > hasn't been any additional comments, please consider pulling the
> > IMA-appraisal patches.
> 
> I thought Dmitry was still waiting on comments from Al for this.

Al NAK'ed the original 'ima: defer calling __fput()' patch from 3/22,
but we addressed both of Al's performance and maintaince concerns in the
last posting on 3/29, which was three weeks ago.  We haven't heard
back ...

>From the 'ima: defer calling __fput()' patch description:

ima_file_free(), which is called on __fput(), updates the file data
hash stored as an extended attribute to reflect file changes.  If a
file is closed before it is munmapped, __fput() is called with the
mmap_sem taken.  With IMA-appraisal enabled, this results in an
mmap_sem/i_mutex lockdep.  ima_defer_fput() increments the f_count to
defer the __fput() being called until after the mmap_sem is released.

The number of __fput() calls needing to be deferred is minimal.  Only
those files in policy, that were closed prior to the munmap and were
mmapped write, need to defer the __fput().

With this patch, on a clean F16 install, from boot to login, only
5 out of ~100,000 mmap_sem held fput() calls were deferred.

Changelog v4:
- ima_defer_fput() performance improvements
- move ima_defer_fput() call from remove_vma() to __fput()
- only defer mmapped files opened for write
- remove unnecessary ima_fput_mempool_destroy()

Mimi

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