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

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Message-ID: <20151004172645.GO19466@redhat.com>
Date:	Sun, 4 Oct 2015 19:26:45 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Chen Gang <xili_gchen_5257@...mail.com>
Cc:	Richard Weinberger <richard.weinberger@...il.com>,
	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>,
	"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

Hello Chen,

On Sun, Oct 04, 2015 at 12:55:29PM +0800, Chen Gang wrote:
> 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.

They don't need to be symmetric because the unlocking order doesn't
matter. To avoid lock inversion deadlocks it is enough to enforce the
lock order.
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