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 0B163C433F5 for ; Mon, 14 Mar 2022 15:21:40 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 644D56B0073; Mon, 14 Mar 2022 11:21:39 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5CDCD8D0001; Mon, 14 Mar 2022 11:21:39 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4469C6B0075; Mon, 14 Mar 2022 11:21:39 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0246.hostedemail.com [216.40.44.246]) by kanga.kvack.org (Postfix) with ESMTP id 32E366B0073 for ; Mon, 14 Mar 2022 11:21:39 -0400 (EDT) Received: from smtpin22.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id D1F68A3086 for ; Mon, 14 Mar 2022 15:21:38 +0000 (UTC) X-FDA: 79243356276.22.BA7FFA2 Received: from out01.mta.xmission.com (out01.mta.xmission.com [166.70.13.231]) by imf02.hostedemail.com (Postfix) with ESMTP id 422968003C for ; Mon, 14 Mar 2022 15:21:38 +0000 (UTC) Received: from in01.mta.xmission.com ([166.70.13.51]:46148) by out01.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1nTmVs-001pwi-O2; Mon, 14 Mar 2022 09:21:36 -0600 Received: from ip68-227-174-4.om.om.cox.net ([68.227.174.4]:37680 helo=email.froward.int.ebiederm.org.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1nTmVr-003ci5-Gz; Mon, 14 Mar 2022 09:21:36 -0600 From: "Eric W. Biederman" To: Miaohe Lin Cc: , , , , Alexey Gladkov References: <20220314064039.62972-1-linmiaohe@huawei.com> Date: Mon, 14 Mar 2022 10:21:10 -0500 In-Reply-To: <20220314064039.62972-1-linmiaohe@huawei.com> (Miaohe Lin's message of "Mon, 14 Mar 2022 14:40:39 +0800") Message-ID: <87h78036hl.fsf@email.froward.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1nTmVr-003ci5-Gz;;;mid=<87h78036hl.fsf@email.froward.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.174.4;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+M0LAEcOvb6LWyXxgtrZneXmnp61b93Kw= X-SA-Exim-Connect-IP: 68.227.174.4 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH v2] mm/mlock: fix potential imbalanced rlimit ucounts adjustment X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) X-Rspamd-Queue-Id: 422968003C X-Rspam-User: Authentication-Results: imf02.hostedemail.com; dkim=none; spf=pass (imf02.hostedemail.com: domain of ebiederm@xmission.com designates 166.70.13.231 as permitted sender) smtp.mailfrom=ebiederm@xmission.com; dmarc=pass (policy=none) header.from=xmission.com X-Stat-Signature: ueurp5iynwru96i4c3snpbjxngw81tps X-Rspamd-Server: rspam07 X-HE-Tag: 1647271298-305431 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: Miaohe Lin writes: > user_shm_lock forgets to set allowed to 0 when get_ucounts fails. So > the later user_shm_unlock might do the extra dec_rlimit_ucounts. Fix > this by resetting allowed to 0. This fix looks correct. But the ability for people to follow and read the code seems questionable. I saw in v1 of this patch Hugh originally misread the logic. Could we instead change the code to leave lock_limit at ULONG_MAX aka RLIM_INFINITY, leave initialized to 0, and not even need a special case of RLIM_INFINITY as nothing can be greater that ULONG_MAX? Something like this? diff --git a/mm/mlock.c b/mm/mlock.c index 8f584eddd305..e7eabf5193ab 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -827,13 +827,12 @@ int user_shm_lock(size_t size, struct ucounts *ucounts) locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT; lock_limit = rlimit(RLIMIT_MEMLOCK); - if (lock_limit == RLIM_INFINITY) - allowed = 1; - lock_limit >>= PAGE_SHIFT; + if (lock_limit != RLIM_INFINITY) + lock_limit >>= PAGE_SHIFT; spin_lock(&shmlock_user_lock); memlock = inc_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked); - if (!allowed && (memlock == LONG_MAX || memlock > lock_limit) && !capable(CAP_IPC_LOCK)) { + if ((memlock == LONG_MAX || memlock > lock_limit) && !capable(CAP_IPC_LOCK)) { dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked); goto out; } > > Fixes: d7c9e99aee48 ("Reimplement RLIMIT_MEMLOCK on top of ucounts") > Signed-off-by: Miaohe Lin > Acked-by: Hugh Dickins > --- > v1->v2: > correct Fixes tag and collect Acked-by tag > Thanks Hugh for review! > --- > mm/mlock.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/mlock.c b/mm/mlock.c > index 29372c0eebe5..efd2dd2943de 100644 > --- a/mm/mlock.c > +++ b/mm/mlock.c > @@ -733,6 +733,7 @@ int user_shm_lock(size_t size, struct ucounts *ucounts) > } > if (!get_ucounts(ucounts)) { > dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked); > + allowed = 0; > goto out; > } > allowed = 1; Eric