linux-kernel - Re: [PATCH] mm/mmap.c: Remove redundant vma looping

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Message-ID: <BLU436-SMTP233624CAE8A4C054B5DFFF8B9490@phx.gbl>
Date:	Sun, 4 Oct 2015 12:55:29 +0800
From:	Chen Gang <xili_gchen_5257@...mail.com>
To:	Richard Weinberger <richard.weinberger@...il.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"riel@...hat.com" <riel@...hat.com>, Michal Hocko <mhocko@...e.cz>,
	"oleg@...hat.com" <oleg@...hat.com>,
	"asha.levin@...cle.com" <asha.levin@...cle.com>,
	"pfeiner@...gle.com" <pfeiner@...gle.com>,
	"aarcange@...hat.com" <aarcange@...hat.com>,
	"vishnu.ps@...sung.com" <vishnu.ps@...sung.com>,
	Linux Memory <linux-mm@...ck.org>,
	kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/mmap.c: Remove redundant vma looping

On 10/4/15 04:09, Richard Weinberger wrote:
> With that change you're reintroducing an issue.
> Please see:
> commit 7cd5a02f54f4c9d16cf7fdffa2122bc73bb09b43
> Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date:   Mon Aug 11 09:30:25 2008 +0200
> 
>     mm: fix mm_take_all_locks() locking order
> 
>     Lockdep spotted:
> 
>     =======================================================
>     [ INFO: possible circular locking dependency detected ]
>     2.6.27-rc1 #270
>     -------------------------------------------------------
>     qemu-kvm/2033 is trying to acquire lock:
>      (&inode->i_data.i_mmap_lock){----}, at: [<ffffffff802996cc>]
> mm_take_all_locks+0xc2/0xea
> 
>     but task is already holding lock:
>      (&anon_vma->lock){----}, at: [<ffffffff8029967a>]
> mm_take_all_locks+0x70/0xea
> 
>     which lock already depends on the new lock.
>

Oh, really. Thanks.

> 
> git blame often explains funky code. :-)
> 

Next, I shall check the git log before make patches, each time. :-)

Theoretically, the lock and unlock need to be symmetric, if we have to
lock f_mapping all firstly, then lock all anon_vma, probably, we also
need to unlock anon_vma all, then unlock all f_mapping.


Thanks.
-- 
Chen Gang (陈刚)

Open, share, and attitude like air, water, and life which God blessed
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