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 E8AA7C3F2C6 for ; Tue, 3 Mar 2020 04:28:13 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9F560214D8 for ; Tue, 3 Mar 2020 04:28:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="F3XTo/Me" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9F560214D8 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 335116B0006; Mon, 2 Mar 2020 23:28:13 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 2E5766B0007; Mon, 2 Mar 2020 23:28:13 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1FA8A6B0008; Mon, 2 Mar 2020 23:28:13 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0036.hostedemail.com [216.40.44.36]) by kanga.kvack.org (Postfix) with ESMTP id 084646B0006 for ; Mon, 2 Mar 2020 23:28:13 -0500 (EST) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id EE0981AB5C for ; Tue, 3 Mar 2020 04:28:12 +0000 (UTC) X-FDA: 76552768824.11.hot55_64c9379e61f2c X-HE-Tag: hot55_64c9379e61f2c X-Filterd-Recvd-Size: 3947 Received: from us-smtp-1.mimecast.com (us-smtp-delivery-1.mimecast.com [207.211.31.120]) by imf11.hostedemail.com (Postfix) with ESMTP for ; Tue, 3 Mar 2020 04:28:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1583209691; h=from:from:reply-to:subject:subject: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=GDMIPd7v29HF3qLCK2yjuGYjUXKITzcTwLkju8pHxl0=; b=F3XTo/Me58nurm4eAJhaClDXqWDzUbvmTy0Z8ksD3/882Ipw4ezzYHi1Qj/bdIKRZTt4kZ XP623aS+if8POl+KugIbeUBaqVNAByYBFWcYJ0AnqGaD3Cbcf2U7NKRUq2RJrxOMhQhsaU ZqVToT2juNyWITfrPdefaQTOAeftkko= 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-185-BfzygFwcMtmV8FItHabr5g-1; Mon, 02 Mar 2020 23:28:09 -0500 X-MC-Unique: BfzygFwcMtmV8FItHabr5g-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 317098017CC; Tue, 3 Mar 2020 04:28:08 +0000 (UTC) Received: from t490s (ovpn-116-88.phx2.redhat.com [10.3.116.88]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A9CB68D568; Tue, 3 Mar 2020 04:28:06 +0000 (UTC) Date: Mon, 2 Mar 2020 23:28:04 -0500 From: Rafael Aquini To: Andrea Arcangeli Cc: Will Deacon , Catalin Marinas , Mark Salter , Jon Masters , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, Michal Hocko , QI Fuli Subject: Re: [PATCH 1/3] mm: use_mm: fix for arches checking mm_users to optimize TLB flushes Message-ID: <20200303042804.GA94763@t490s> References: <20200223192520.20808-1-aarcange@redhat.com> <20200223192520.20808-2-aarcange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200223192520.20808-2-aarcange@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 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 Sun, Feb 23, 2020 at 02:25:18PM -0500, Andrea Arcangeli wrote: > 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 = mm; > } > + mmget(mm); > tsk->mm = 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 = NULL; > + mmput(mm); > /* active_mm is still 'mm' */ > enter_lazy_tlb(mm, tsk); > task_unlock(tsk); Acked-by: Rafael Aquini