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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AD1A3C433F5 for ; Wed, 25 May 2022 08:32:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234649AbiEYIc5 (ORCPT ); Wed, 25 May 2022 04:32:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36550 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232132AbiEYIct (ORCPT ); Wed, 25 May 2022 04:32:49 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8912355AD for ; Wed, 25 May 2022 01:32:48 -0700 (PDT) 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 477771F8F0; Wed, 25 May 2022 08:32:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1653467567; 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=pk+dd2y8fS3J24I3QMHCkhSgrc5nc+xtSy/Ob44ezc0=; b=jc6opkF5ItJgVXPTi9F0j+aaujkMIUL4mbOsyNv4Q0uYjYK8PDPtwC4M8niexkl2Gz1eui tJ7iASKcqkKsAAtpobalW41w/X3C8AH1EAzIuGxZNx6I7IeV48Me18ZVZ4pl0IwQ4XMZwe ts/ugyOu/jCufHit3sYu9hRwrhvlfwU= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1653467567; 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=pk+dd2y8fS3J24I3QMHCkhSgrc5nc+xtSy/Ob44ezc0=; b=XcS0O9FxCGxfIAwhK11cUm4XWwsDlPPMeQ2FyuxBDE9HSlwmRzGawapDum1F0ZyLDgY1VG PIxw34wc31TcrCCw== 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 D91C713ADF; Wed, 25 May 2022 08:32:45 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id rz0tMq3pjWLONwAAMHmgww (envelope-from ); Wed, 25 May 2022 08:32:45 +0000 Date: Wed, 25 May 2022 10:32:43 +0200 From: Oscar Salvador To: Miaohe Lin Cc: akpm@linux-foundation.org, mike.kravetz@oracle.com, naoya.horiguchi@nec.com, peterx@redhat.com, apopple@nvidia.com, ying.huang@intel.com, david@redhat.com, songmuchun@bytedance.com, hch@lst.de, dhowells@redhat.com, cl@linux.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 1/4] mm: reduce the rcu lock duration Message-ID: References: <20220525081822.53547-1-linmiaohe@huawei.com> <20220525081822.53547-2-linmiaohe@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220525081822.53547-2-linmiaohe@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 25, 2022 at 04:18:19PM +0800, Miaohe Lin wrote: > Commit 3268c63eded4 ("mm: fix move/migrate_pages() race on task struct") > extends the period of the rcu_read_lock until after the permissions checks > are done to prevent the task pointed to from changing from under us. But > the task_struct refcount is also taken at that time, the reference to task > is guaranteed to be stable. So it's unnecessary to extend the period of > the rcu_read_lock. Release the rcu lock after task refcount is successfully > grabbed to reduce the rcu holding time. > > Reviewed-by: Muchun Song > Reviewed-by: Christoph Hellwig > Signed-off-by: Miaohe Lin > Cc: Huang Ying > Cc: David Howells > Cc: Christoph Lameter Reviewed-by: Oscar Salvador > --- > mm/mempolicy.c | 3 +-- > mm/migrate.c | 3 +-- > 2 files changed, 2 insertions(+), 4 deletions(-) > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index 0b4ba3ee810e..2dad094177bf 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -1609,6 +1609,7 @@ static int kernel_migrate_pages(pid_t pid, unsigned long maxnode, > goto out; > } > get_task_struct(task); > + rcu_read_unlock(); > > err = -EINVAL; > > @@ -1617,11 +1618,9 @@ static int kernel_migrate_pages(pid_t pid, unsigned long maxnode, > * Use the regular "ptrace_may_access()" checks. > */ > if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) { > - rcu_read_unlock(); > err = -EPERM; > goto out_put; > } > - rcu_read_unlock(); > > task_nodes = cpuset_mems_allowed(task); > /* Is the user allowed to access the target nodes? */ > diff --git a/mm/migrate.c b/mm/migrate.c > index e51588e95f57..e88ebb88fa6f 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1902,17 +1902,16 @@ static struct mm_struct *find_mm_struct(pid_t pid, nodemask_t *mem_nodes) > return ERR_PTR(-ESRCH); > } > get_task_struct(task); > + rcu_read_unlock(); > > /* > * Check if this process has the right to modify the specified > * process. Use the regular "ptrace_may_access()" checks. > */ > if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) { > - rcu_read_unlock(); > mm = ERR_PTR(-EPERM); > goto out; > } > - rcu_read_unlock(); > > mm = ERR_PTR(security_task_movememory(task)); > if (IS_ERR(mm)) > -- > 2.23.0 > > -- Oscar Salvador SUSE Labs