From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta8.messagelabs.com (mail6.bemta8.messagelabs.com [216.82.243.55]) by kanga.kvack.org (Postfix) with ESMTP id 7D6AB6B0069 for ; Fri, 18 Nov 2011 10:23:14 -0500 (EST) Received: by wwf10 with SMTP id 10so4427543wwf.26 for ; Fri, 18 Nov 2011 07:23:12 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20111118150742.GA23223@tiehlicka.suse.cz> References: <20111118150742.GA23223@tiehlicka.suse.cz> Date: Fri, 18 Nov 2011 23:23:12 +0800 Message-ID: Subject: Re: [PATCH] hugetlb: detect race if fail to COW From: Hillf Danton Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrea Arcangeli , Andrew Morton , Johannes Weiner , linux-mm@kvack.org, LKML On Fri, Nov 18, 2011 at 11:07 PM, Michal Hocko wrote: > On Fri 18-11-11 22:04:37, Hillf Danton wrote: >> In the error path that we fail to allocate new huge page, before try again, we >> have to check race since page_table_lock is re-acquired. > > I do not think we can race here because we are serialized by > hugetlb_instantiation_mutex AFAIU. Without this lock, however, we could > fall into avoidcopy and shortcut despite the fact that other thread has > already did the job. > > The mutex usage is not obvious in hugetlb_cow so maybe we want to be > explicit about it (either a comment or do the recheck). > Then the following check is unnecessary, no? Thanks, Hillf /* * Retake the page_table_lock to check for racing updates * before the page tables are altered */ spin_lock(&mm->page_table_lock); ptep = huge_pte_offset(mm, address & huge_page_mask(h)); if (likely(pte_same(huge_ptep_get(ptep), pte))) { /* Break COW */ -- 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