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[209.132.183.28]) by mx.google.com with ESMTPS id x5si147026qvc.136.2019.03.25.15.56.40 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Mar 2019 15:56:40 -0700 (PDT) Received-SPF: pass (google.com: domain of aarcange@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of aarcange@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=aarcange@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 788ED3086262; Mon, 25 Mar 2019 22:56:39 +0000 (UTC) Received: from sky.random (ovpn-120-118.rdu2.redhat.com [10.10.120.118]) by smtp.corp.redhat.com (Postfix) with ESMTPS id F1E2E642B5; Mon, 25 Mar 2019 22:56:36 +0000 (UTC) From: Andrea Arcangeli To: Andrew Morton Cc: linux-mm@kvack.org, zhong jiang , syzkaller-bugs@googlegroups.com, syzbot+cbb52e396df3e565ab02@syzkaller.appspotmail.com, Mike Rapoport , Mike Kravetz , Peter Xu , Dmitry Vyukov Subject: [PATCH 2/2] mm: change mm_update_next_owner() to update mm->owner with WRITE_ONCE Date: Mon, 25 Mar 2019 18:56:36 -0400 Message-Id: <20190325225636.11635-3-aarcange@redhat.com> In-Reply-To: <20190325225636.11635-1-aarcange@redhat.com> References: <20190325225636.11635-1-aarcange@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.49]); Mon, 25 Mar 2019 22:56:39 +0000 (UTC) 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: X-Virus-Scanned: ClamAV using ClamSMTP The RCU reader uses rcu_dereference() inside rcu_read_lock critical sections, so the writer shall use WRITE_ONCE. Just a cleanup, we still rely on gcc to emit atomic writes in other places. Signed-off-by: Andrea Arcangeli --- kernel/exit.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/exit.c b/kernel/exit.c index 2166c2d92ddc..8361a560cd1d 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -422,7 +422,7 @@ void mm_update_next_owner(struct mm_struct *mm) * freed task structure. */ if (atomic_read(&mm->mm_users) <= 1) { - mm->owner = NULL; + WRITE_ONCE(mm->owner, NULL); return; } @@ -462,7 +462,7 @@ void mm_update_next_owner(struct mm_struct *mm) * most likely racing with swapoff (try_to_unuse()) or /proc or * ptrace or page migration (get_task_mm()). Mark owner as NULL. */ - mm->owner = NULL; + WRITE_ONCE(mm->owner, NULL); return; assign_new_owner: @@ -483,7 +483,7 @@ void mm_update_next_owner(struct mm_struct *mm) put_task_struct(c); goto retry; } - mm->owner = c; + WRITE_ONCE(mm->owner, c); task_unlock(c); put_task_struct(c); }