From: Vladimir Davydov <vdavydov@parallels.com>
To: yalin wang <yalin.wang2010@gmail.com>
Cc: Rik van Riel <riel@redhat.com>, Hugh Dickins <hughd@google.com>,
Christoph Lameter <cl@linux.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Peter Zijlstra <peterz@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
Minchan Kim <minchan@kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@suse.cz>, Greg Thelen <gthelen@google.com>,
Michel Lespinasse <walken@google.com>,
David Rientjes <rientjes@google.com>,
Pavel Emelyanov <xemul@parallels.com>,
Cyrill Gorcunov <gorcunov@openvz.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC] rmap: fix "race" between do_wp_page and shrink_active_list
Date: Tue, 12 May 2015 11:34:38 +0300 [thread overview]
Message-ID: <20150512083438.GB17628@esperanza> (raw)
In-Reply-To: <CAFP4FLoPfisZib3SQeeW57U6NPxnpd=rNRgiv9OOsYDrFWd=6A@mail.gmail.com>
On Mon, May 11, 2015 at 04:59:27PM +0800, yalin wang wrote:
> i am confused about your analysis ,
> for the race stack:
>
> CPU0 CPU1
>
> ---- ----
>
> do_wp_page shrink_active_list
>
> lock_page page_referenced
>
> PageAnon->yes, so skip trylock_page
>
> page_move_anon_rmap
>
> page->mapping = anon_vma
>
> rmap_walk
>
> PageAnon->no
>
> rmap_walk_file
>
> BUG
>
> page->mapping += PAGE_MAPPING_ANON
>
> the page should must change from PageAnon() to !PageAnon() when crash happened.
> but page_move_anon_rmap() is doing change a page from !PageAnon()
> (swapcache page) to PageAnon() ,
A swapcache page is not necessarily !PageAnon. In do_wp_page() old_page
*is* PageAnon. It may or may not be on the swapcache though, which does
not really matter.
> how does this race condition crash happened ?
It never happened. It might theoretically happen due to a compiler
"optimization" I described above.
Thanks,
Vladimir
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next prev parent reply other threads:[~2015-05-12 8:34 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-11 7:51 Vladimir Davydov
2015-05-11 8:59 ` yalin wang
2015-05-12 8:34 ` Vladimir Davydov [this message]
2015-05-17 12:44 ` yalin
2015-05-11 9:36 ` Kirill A. Shutemov
2015-05-12 9:27 ` Vladimir Davydov
2015-05-11 14:24 ` Paul E. McKenney
2015-05-12 9:31 ` Vladimir Davydov
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