Re: page fault fastpath patch v2: fix race conditions, stats for 8,32 and 512 cpu SMP

From: Rajesh Venkatasubramanian <vrajesh_at_umich.edu>
Date: 2004-08-19 10:07:24
On Wed, 18 Aug 2004, William Lee Irwin III wrote:

> William Lee Irwin III wrote:
> >> It also protects against vma tree modifications in mainline, but rmap.c
> >> shouldn't need it for vmas anymore, as the vma is rooted to the spot by
> >> mapping->i_shared_lock for file pages and anon_vma->lock for anonymous.
>
> On Wed, Aug 18, 2004 at 07:50:21PM -0400, Rajesh Venkatasubramanian wrote:
> > If I am reading the code correctly, then without page_table_lock
> > in page_referenced_one(), we can race with exit_mmap() and page
> > table pages can be freed under us.
>
> exit_mmap() has removed the vma from ->i_mmap and ->mmap prior to
> unmapping the pages, so this should be safe unless that operation
> can be caught while it's in progress.

No. Unfortunately exit_mmap() removes vmas from ->i_mmap after removing
page table pages. Maybe we can reverse this, though.

Rajesh

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Received on Wed Aug 18 20:09:33 2004

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