From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx122.postini.com [74.125.245.122]) by kanga.kvack.org (Postfix) with SMTP id D6FF36B005C for ; Wed, 11 Jan 2012 07:06:32 -0500 (EST) Received: by wics10 with SMTP id s10so425192wic.14 for ; Wed, 11 Jan 2012 04:06:31 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20120104151632.05e6b3b0.akpm@linux-foundation.org> References: <20111222163604.GB14983@tiehlicka.suse.cz> <20120104151632.05e6b3b0.akpm@linux-foundation.org> Date: Wed, 11 Jan 2012 20:06:30 +0800 Message-ID: Subject: Re: [PATCH] mm: hugetlb: undo change to page mapcount in fault handler From: Hillf Danton Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Michal Hocko , linux-mm@kvack.org, LKML , KAMEZAWA Hiroyuki On Thu, Jan 5, 2012 at 7:16 AM, Andrew Morton w= rote: > On Fri, 23 Dec 2011 21:00:41 +0800 > Hillf Danton wrote: > >> Page mapcount should be updated only if we are sure that the page ends >> up in the page table otherwise we would leak if we couldn't COW due to >> reservations or if idx is out of bounds. > > It would be much nicer if we could run vma_needs_reservation() before > even looking up or allocating the page. > > And afaict the interface is set up to do that: you run > vma_needs_reservation() before allocating the page and then > vma_commit_reservation() afterwards. > > But hugetlb_no_page() and hugetlb_fault() appear to have forgotten to > run vma_commit_reservation() altogether. =C2=A0Why isn't this as busted a= s > it appears to be? Hi Andrew IIUC the two operations, vma_{needs, commit}_reservation, are folded in alloc_huge_page(), need to break the pair? Thanks Hillf -- 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 internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org