From: yalin <yalin.wang2010@gmail.com>
To: Vladimir Davydov <vdavydov@parallels.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: Sun, 17 May 2015 20:44:12 +0800 [thread overview]
Message-ID: <55588D1C.5060900@gmail.com> (raw)
In-Reply-To: <20150512083438.GB17628@esperanza>
> 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.
i see,
Thanks for your explanation!
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WARNING: multiple messages have this Message-ID (diff)
From: yalin <yalin.wang2010@gmail.com>
To: Vladimir Davydov <vdavydov@parallels.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: Sun, 17 May 2015 20:44:12 +0800 [thread overview]
Message-ID: <55588D1C.5060900@gmail.com> (raw)
In-Reply-To: <20150512083438.GB17628@esperanza>
> 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.
i see,
Thanks for your explanation!
next prev parent reply other threads:[~2015-05-17 12:48 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-11 7:51 [RFC] rmap: fix "race" between do_wp_page and shrink_active_list Vladimir Davydov
2015-05-11 7:51 ` Vladimir Davydov
2015-05-11 8:59 ` yalin wang
2015-05-11 8:59 ` yalin wang
2015-05-12 8:34 ` Vladimir Davydov
2015-05-12 8:34 ` Vladimir Davydov
2015-05-17 12:44 ` yalin [this message]
2015-05-17 12:44 ` yalin
2015-05-11 9:36 ` Kirill A. Shutemov
2015-05-11 9:36 ` Kirill A. Shutemov
2015-05-12 9:27 ` Vladimir Davydov
2015-05-12 9:27 ` Vladimir Davydov
2015-05-11 14:24 ` Paul E. McKenney
2015-05-11 14:24 ` Paul E. McKenney
2015-05-12 9:31 ` Vladimir Davydov
2015-05-12 9:31 ` Vladimir Davydov
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