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 X-Spam-Level: X-Spam-Status: No, score=-6.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8E2CBC35247 for ; Mon, 3 Feb 2020 20:17:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 55E3020720 for ; Mon, 3 Feb 2020 20:17:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Ff6oMpOK" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726994AbgBCURx (ORCPT ); Mon, 3 Feb 2020 15:17:53 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:53037 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726250AbgBCURx (ORCPT ); Mon, 3 Feb 2020 15:17:53 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1580761072; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=WdAkDw0jQFrUByye8xgaI8zjWL8waIYULZhRupYTANc=; b=Ff6oMpOKcL3QUT9K5r+MDf8YHMPc5daoEolmcrmPWAn+DlHcGWUo4GbUq7jiiDDc1INTyl iDh3j3bxmrdBBnuiJtrFCdPKAl99mnyg+E/ucHdHge1xVabE8LzgVJqsDc21swKojzICu3 5YXsAwCvrulDv2vsBkAYNtlnQHchuyw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-247-LVTmi57UP5CtwO7-hrd4wA-1; Mon, 03 Feb 2020 15:17:50 -0500 X-MC-Unique: LVTmi57UP5CtwO7-hrd4wA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B667D13E5; Mon, 3 Feb 2020 20:17:48 +0000 (UTC) Received: from mail (ovpn-120-67.rdu2.redhat.com [10.10.120.67]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0D78B1001B09; Mon, 3 Feb 2020 20:17:46 +0000 (UTC) From: Andrea Arcangeli To: Will Deacon , Catalin Marinas , Jon Masters , Rafael Aquini , Mark Salter Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org Subject: [PATCH 1/2] mm: use_mm: fix for arches checking mm_users to optimize TLB flushes Date: Mon, 3 Feb 2020 15:17:44 -0500 Message-Id: <20200203201745.29986-2-aarcange@redhat.com> In-Reply-To: <20200203201745.29986-1-aarcange@redhat.com> References: <20200203201745.29986-1-aarcange@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org alpha, ia64, mips, powerpc, sh, sparc are relying on a check on mm->mm_users to know if they can skip some remote TLB flushes for single threaded processes. Most callers of use_mm() tend to invoke mmget_not_zero() or get_task_mm() before use_mm() to ensure the mm will remain alive in between use_mm() and unuse_mm(). Some callers however don't increase mm_users and they instead rely on serialization in __mmput() to ensure the mm will remain alive in between use_mm() and unuse_mm(). Not increasing mm_users during use_mm() is however unsafe for aforementioned arch TLB flushes optimizations. So either mmget()/mmput() should be added to the problematic callers of use_mm()/unuse_mm() or we can embed them in use_mm()/unuse_mm() which is more robust. Signed-off-by: Andrea Arcangeli --- mm/mmu_context.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/mmu_context.c b/mm/mmu_context.c index 3e612ae748e9..ced0e1218c0f 100644 --- a/mm/mmu_context.c +++ b/mm/mmu_context.c @@ -30,6 +30,7 @@ void use_mm(struct mm_struct *mm) mmgrab(mm); tsk->active_mm =3D mm; } + mmget(mm); tsk->mm =3D mm; switch_mm(active_mm, mm, tsk); task_unlock(tsk); @@ -57,6 +58,7 @@ void unuse_mm(struct mm_struct *mm) task_lock(tsk); sync_mm_rss(mm); tsk->mm =3D NULL; + mmput(mm); /* active_mm is still 'mm' */ enter_lazy_tlb(mm, tsk); task_unlock(tsk);