From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx193.postini.com [74.125.245.193]) by kanga.kvack.org (Postfix) with SMTP id D58CC6B0044 for ; Wed, 5 Dec 2012 01:28:36 -0500 (EST) Received: by mail-pb0-f41.google.com with SMTP id xa7so3552938pbc.14 for ; Tue, 04 Dec 2012 22:28:36 -0800 (PST) Date: Tue, 4 Dec 2012 22:28:33 -0800 (PST) From: Hugh Dickins Subject: Re: [PATCH 5/5] mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma() In-Reply-To: Message-ID: References: <1349801921-16598-1-git-send-email-mgorman@suse.de> <1349801921-16598-6-git-send-email-mgorman@suse.de> <20121204141501.GA2797@suse.de> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Tommi Rantala , Stable , Andi Kleen , Andrew Morton , KOSAKI Motohiro , Dave Jones , Christoph Lameter , LKML , Linux-MM On Tue, 4 Dec 2012, Hugh Dickins wrote: > > Yes, your patch fixes it Mel, but I prefer it as below, with a couple > of mods: removing the no longer true comment, and leaving shmem_swapin() > alone with just a comment. It appears to be the job of the rather weird > mpol_cond_copy() to drop the reference on the original mempolicy, and > clear MPOL_F_SHARED so the copy won't need one (it's trying to cope with > the fact that swapin_readahead will make an unknown number of calls to > alloc_page_vma). So I'd rather not add another mpol_cond_put there, > whose cond will never be met. Hold on, ignore that patch for now, I think I had my priorities upside down: it would be better for shmem_swapin() to behave as you proposed, and we delete the mpol_cond_copy() weirdness instead. Your 00442ad04a5e changed alloc_pages_vma() to keep its refcounting in balance, so it now does not matter that swapin_readahead() makes an unknown number of calls to it: we should simply take a reference before and drop it after, just as you do in shmem_alloc_page(). I'd still like to revisit alloc_page_vma(), and its refcount manipulations do now appear redundant; but changing that is not something I want to get into in a last minute rush. But getting rid of mpol_cond_copy() should be safe and clear, I'll test that out now and reply with an updated patch (or else admit I got confused). Hugh -- 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/ . Don't email: email@kvack.org