From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Lameter <christoph@lameter.com>
Date: Mon, 23 Aug 2004 23:35:12 +0000
Subject: Re: page fault fastpath patch v2: fix race conditions, stats for
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To: Rajesh Venkatasubramanian <vrajesh@umich.edu>
Cc: William Lee Irwin III <wli@holomorphy.com>, Hugh Dickins <hugh@veritas.com>, "David S. Miller" <davem@redhat.com>, raybry@sgi.com, ak@muc.de, benh@kernel.crashing.org, manfred@colorfullife.com, linux-ia64@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>

On Mon, 23 Aug 2004, Rajesh Venkatasubramanian wrote:

> So there are no other active thread (mm_user) other than the current
> exit_mmap() thread. This gives thread exclusion. So we don't need
> mm->mmap_sem.
>
> However, we have to lock out truncate()->zap_pmd_range(), rmap.c
> functions, and other places from walking the page tables while we
> are freeing the page tables in exit_mmap(). The page_table_lock in
> exit_mmap() provides that exclusion.
>
> That's my understanding. Correct me if I am wrong.

Correct. I just looked through the function and it unlinks the pgd before
unlocking page_table_lock. It frees the pgd tree content later.

Since no mm_user is active anymore no pte ops occur and therefore also
atomic pte operations do not need protection.