Date: Fri, 26 Oct 2012 16:14:30 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, Andrea Arcangeli <aarcange@redhat.com>,
        Mel Gorman <mgorman@suse.de>, Johannes Weiner <hannes@cmpxchg.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 26/31] sched, numa, mm: Add fault driven placement and
 migration policy
Message-ID: <20121026141430.GA12158@gmail.com>
References: <20121025121617.617683848@chello.nl>
 <20121025124834.467791319@chello.nl>
 <CA+55aFwJdn8Kz9UByuRfGNtf9Hkv-=8xB+WRd47uHZU1YMagZw@mail.gmail.com>
 <20121026071532.GC8141@gmail.com>
 <20121026135024.GA11640@gmail.com>
 <1351260672.16863.81.camel@twins>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1351260672.16863.81.camel@twins>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 896
Lines: 31


* Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> On Fri, 2012-10-26 at 15:50 +0200, Ingo Molnar wrote:
> > 
> > Oh, just found the reason:
> > 
> > the ptep_modify_prot_start()/modify()/commit() sequence is 
> > SMP-unsafe - it has to be done under the mmap_sem 
> > write-locked.
> > 
> > It is safe against *hardware* updates to the PTE, but not 
> > safe against itself.
> 
> Shouldn't the pte_lock serialize all that still? All sites 
> that modify PTE contents should hold the pte_lock (and do 
> afaict).

Hm, indeed.

Is there no code under down_read() (in the page fault path) that 
modifies the pte via just pure atomics?

Thanks,

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/