From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id 82BFC6B0087 for ; Thu, 9 Dec 2010 02:50:05 -0500 (EST) Received: from wpaz9.hot.corp.google.com (wpaz9.hot.corp.google.com [172.24.198.73]) by smtp-out.google.com with ESMTP id oB97o3dQ006455 for ; Wed, 8 Dec 2010 23:50:03 -0800 Received: from pvd12 (pvd12.prod.google.com [10.241.209.204]) by wpaz9.hot.corp.google.com with ESMTP id oB97njeG011424 for ; Wed, 8 Dec 2010 23:50:02 -0800 Received: by pvd12 with SMTP id 12so495527pvd.34 for ; Wed, 08 Dec 2010 23:50:02 -0800 (PST) From: Michel Lespinasse Subject: [PATCH 0/2] RFC: page munlock issues when breaking up COW Date: Wed, 8 Dec 2010 23:49:37 -0800 Message-Id: <1291880979-16309-1-git-send-email-walken@google.com> Sender: owner-linux-mm@kvack.org To: Nick Piggin , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org List-ID: I'm sending this up as RFC only as I've only done minimal testing so far - I would actually be particularly interested in comments about any corner cases I must make sure to test for... It looks like there is a race in the do_wp_page() code that munlocks the old page after breaking up COW. The pte still points to that old page, so I don't see that we are protected against vmscan mlocking back the page right away. This can be easily worked around by moving that code to the end of do_wp_page(), after the pte has been pointed to the new page. Also, the corresponding code in __do_fault() seems entirely unnecessary, since there was never a pte pointing to the old page in our vma. I found this by code inspection only, and while I believe I understand this code well by now, there is always the possibility that I may have missed something. I hope Nick can comment, since he wrote this part of the code. Michel Lespinasse (2): mlock: fix race when munlocking pages in do_wp_page() mlock: do not munlock pages in __do_fault() mm/memory.c | 32 ++++++++++++-------------------- 1 files changed, 12 insertions(+), 20 deletions(-) -- 1.7.3.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org