From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id DB3F0CD54A9 for ; Tue, 19 Sep 2023 08:53:02 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 592FC6B04D7; Tue, 19 Sep 2023 04:53:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 543306B04D8; Tue, 19 Sep 2023 04:53:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3E4BA6B04D9; Tue, 19 Sep 2023 04:53:02 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 2B53F6B04D7 for ; Tue, 19 Sep 2023 04:53:02 -0400 (EDT) Received: from smtpin05.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 04223B3D7E for ; Tue, 19 Sep 2023 08:53:01 +0000 (UTC) X-FDA: 81252732204.05.1620F68 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by imf23.hostedemail.com (Postfix) with ESMTP id 0F6D714001B for ; Tue, 19 Sep 2023 08:52:59 +0000 (UTC) Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=siGFRRKW; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf23.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1695113580; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=MAE/ORI96UNcZCy9nD+5Kv3FH7y5O9zbGLIgTktz+G8=; b=Bs0ULuYwzGg8R4nqalsglJUidnQ8kvr2YIJvsAcRHbV8P1ZzB5ido+Amt/qrcNOiZNJ9Wy ijOffFG9OodZ/C/iTsQU2wzlfVPibkWIfJZ4NPliazUpoSqAhT+Ratz2cXeW3ear9Jklj/ Ol2SUm0OCVIWY8aifNM8GT8gjwifoOs= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=siGFRRKW; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf23.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1695113580; a=rsa-sha256; cv=none; b=eLyeSSc8Det73kX34TLy8RISwzsGNk5uNG1MYvPIh34T+uG8nmL/aaZcOFBDCchXSkYnTv pItnOV4m9U8BwkLnBCE2BlhRkwwW5pbf162ADbWLxUjMInZdB6QyYENZYtFSTtNsXX9t5y LyyS2VvIlzUh1p5zOmuwUMdIZHrDpmw= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id E24421FE39; Tue, 19 Sep 2023 08:52:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1695113577; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=MAE/ORI96UNcZCy9nD+5Kv3FH7y5O9zbGLIgTktz+G8=; b=siGFRRKWVi99Szw+lvvhO2kvgTV+hFfPuVd9w12MtY+OehkIiJL0w5SixQa1n/DIlzBaLa H50OUF9DIHnwiiGCUkv1lmcZddYcd618rmdrZJ3r8PCb3rsxL8Pxoj40y8CZXiWkG0CjLe 82KB4FY8CHO3mQh2wJBbaE6I5maF9w8= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id B5F8C134F3; Tue, 19 Sep 2023 08:52:57 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id sUmWKWlhCWUJGgAAMHmgww (envelope-from ); Tue, 19 Sep 2023 08:52:57 +0000 Date: Tue, 19 Sep 2023 10:52:56 +0200 From: Michal Hocko To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, willy@infradead.org, hughd@google.com, shy828301@gmail.com, vbabka@suse.cz, syzkaller-bugs@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+b591856e0f0139f83023@syzkaller.appspotmail.com Subject: Re: [PATCH 1/1] mm: lock VMAs skipped by a failed queue_pages_range() Message-ID: References: <20230918211608.3580629-1-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230918211608.3580629-1-surenb@google.com> X-Rspamd-Queue-Id: 0F6D714001B X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: 7qthe1uz66ghog4f554p9f46uidyyfei X-HE-Tag: 1695113579-704840 X-HE-Meta: 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 qKLqyJiX 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon 18-09-23 14:16:08, Suren Baghdasaryan wrote: > When queue_pages_range() encounters an unmovable page, it terminates > its page walk. This walk, among other things, locks the VMAs in the range. > This termination might result in some VMAs being left unlock after > queue_pages_range() completes. Since do_mbind() continues to operate on > these VMAs despite the failure from queue_pages_range(), it will encounter > an unlocked VMA. > This mbind() behavior has been modified several times before and might > need some changes to either finish the page walk even in the presence > of unmovable pages or to error out immediately after the failure to > queue_pages_range(). However that requires more discussions, so to > fix the immediate issue, explicitly lock the VMAs in the range if > queue_pages_range() failed. The added condition does not save much > but is added for documentation purposes to understand when this extra > locking is needed. The semantic of the walk in this case is really clear as mud. I was trying to reconstruct the whole picture and it really hurts... Then I found http://lkml.kernel.org/r/CAHbLzkrmTaqBRmHVdE2kyW57Uoghqd_E+jAXC9cB5ofkhL-uvw@mail.gmail.com and that helped a lot. Let's keep it a reference at least in the email thread here for future. > Fixes: 49b0638502da ("mm: enable page walking API to lock vmas during the walk") > Reported-by: syzbot+b591856e0f0139f83023@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/all/000000000000f392a60604a65085@google.com/ > Signed-off-by: Suren Baghdasaryan I cannot say I like the patch (it looks like a potential double locking unless you realize this lock is special) but considering this might be just temporal I do not mind. Acked-by: Michal Hocko Thanks! > --- > mm/mempolicy.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index 42b5567e3773..cbc584e9b6ca 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -1342,6 +1342,9 @@ static long do_mbind(unsigned long start, unsigned long len, > vma_iter_init(&vmi, mm, start); > prev = vma_prev(&vmi); > for_each_vma_range(vmi, vma, end) { > + /* If queue_pages_range failed then not all VMAs might be locked */ > + if (ret) > + vma_start_write(vma); > err = mbind_range(&vmi, vma, &prev, start, end, new); > if (err) > break; > -- > 2.42.0.459.ge4e396fd5e-goog -- Michal Hocko SUSE Labs