Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755393AbbK3WKZ (ORCPT ); Mon, 30 Nov 2015 17:10:25 -0500 Received: from mail-pa0-f47.google.com ([209.85.220.47]:35755 "EHLO mail-pa0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755376AbbK3WKT (ORCPT ); Mon, 30 Nov 2015 17:10:19 -0500 Date: Mon, 30 Nov 2015 14:10:16 -0800 (PST) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Naoya Horiguchi cc: Andrew Morton , Hugh Dickins , Dave Hansen , Mel Gorman , Joonsoo Kim , Hillf Danton , Mike Kravetz , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Naoya Horiguchi Subject: Re: [PATCH v1] mm: hugetlb: call huge_pte_alloc() only if ptep is null In-Reply-To: <1448524936-10501-1-git-send-email-n-horiguchi@ah.jp.nec.com> Message-ID: References: <1448524936-10501-1-git-send-email-n-horiguchi@ah.jp.nec.com> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1413 Lines: 29 On Thu, 26 Nov 2015, Naoya Horiguchi wrote: > Currently at the beginning of hugetlb_fault(), we call huge_pte_offset() > and check whether the obtained *ptep is a migration/hwpoison entry or not. > And if not, then we get to call huge_pte_alloc(). This is racy because the > *ptep could turn into migration/hwpoison entry after the huge_pte_offset() > check. This race results in BUG_ON in huge_pte_alloc(). > > We don't have to call huge_pte_alloc() when the huge_pte_offset() returns > non-NULL, so let's fix this bug with moving the code into else block. > > Note that the *ptep could turn into a migration/hwpoison entry after > this block, but that's not a problem because we have another !pte_present > check later (we never go into hugetlb_no_page() in that case.) > > Fixes: 290408d4a250 ("hugetlb: hugepage migration core") > Signed-off-by: Naoya Horiguchi > Cc: [2.6.36+] Acked-by: David Rientjes It would be nice to provide a sample of the BUG_ON() output in the commit message, however, so people can quickly find this if greping for what they just saw kill their machine. -- 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/