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=-14.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=unavailable 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 AF078C3F2D1 for ; Mon, 2 Mar 2020 16:33:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4738C21D56 for ; Mon, 2 Mar 2020 16:33:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="gjBc7d6Y" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727060AbgCBQc6 (ORCPT ); Mon, 2 Mar 2020 11:32:58 -0500 Received: from mail-vk1-f196.google.com ([209.85.221.196]:34436 "EHLO mail-vk1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727112AbgCBQc5 (ORCPT ); Mon, 2 Mar 2020 11:32:57 -0500 Received: by mail-vk1-f196.google.com with SMTP id w67so3133985vkf.1 for ; Mon, 02 Mar 2020 08:32:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=6G1UATj4krZxsCknjrQEeeFai91FPwBe7XfsjRuVvR4=; b=gjBc7d6YnjDc2NB2v1tqHbdmYRA6US1Zc4Bwdfw5pIWhSmmK+Bim0XXVC967za6mwx ttu/8XEIGHY+D5pOwYhrSNHH/c4SoLvoncF5LehwoF40RSVQ9t9odVgxLiDlcLjFr8Qf uXYk5vh3osEyjqmPttQL18i1ib4MEU32Qt3I2R3oe2JnmiK3Jik/inzsusGzwGnwm8pV s1va7f8IYUZ7uLxzJUgWIyTWYsii4w3rsSFeFJeDn2VTka/qdtcbcgiRxqnQuUa+AYgx 0sFVAYTtpPKHuI2iqRu7GbzoyP3paHDugM7UXOnTi6wNwOQFMIQx2OSWfFXbxa+LWAu3 a1yw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=6G1UATj4krZxsCknjrQEeeFai91FPwBe7XfsjRuVvR4=; b=Jr7oVzKlWmTxHMx8PG3NjEYWbJegcquYNwZkzQ7kw1j4TKnotELWm+4kZeLoatbNO6 iCsGsG594+1dzIYwoPa5cc+N01Sp4WIGUTYps7op0vOvIUE/fzwT9AQZvh71g1hyr2Hc OReiORYZGdfevJiMivoMrPxF/as4JxB2YCHnPTEjxLBsy55v2S/o7FKEOo1rT9kMsiDB kEBIeEHyw6LzVo0iTcDIObkdoTFHl3LOFi4bjSMznrPniMMslUmcyXtkiVX8SL7vV7E6 auRl5wYDnYTMxnJLnnv5o65MWnHBUJW8qQEC1jDwAkMaK5MJz946gTHpioTdSMsY1na6 WJhw== X-Gm-Message-State: ANhLgQ0RfmkTNFUQB8wvK3xsbvwqmxcdQozIE/aq7wq6LoaXR//FCDOi psPZ/WKERB8ZLdn5FVN/JxzIa59KVy09FNTiMl1uWw== X-Google-Smtp-Source: ADFU+vudr5OddUJOm/nCflCRNBR8hUNIZhkJyQ8IXmQMh0kL9nYnxmTqjHWz5AHVu0pL2BiPYiLALTBK7m4MdHvpN+w= X-Received: by 2002:ac5:c914:: with SMTP id t20mr334096vkl.37.1583166775011; Mon, 02 Mar 2020 08:32:55 -0800 (PST) MIME-Version: 1.0 References: <20200219014433.88424-1-minchan@kernel.org> <20200219014433.88424-7-minchan@kernel.org> <20200302073332.gn7lvhxmmv5pupyq@butterfly.localdomain> In-Reply-To: <20200302073332.gn7lvhxmmv5pupyq@butterfly.localdomain> From: Suren Baghdasaryan Date: Mon, 2 Mar 2020 08:32:44 -0800 Message-ID: Subject: Re: [PATCH v6 6/7] mm/madvise: employ mmget_still_valid for write lock To: Oleksandr Natalenko Cc: Minchan Kim , Andrew Morton , LKML , linux-mm , linux-api@vger.kernel.org, Tim Murray , Daniel Colascione , Sandeep Patil , Sonny Rao , Brian Geffon , Michal Hocko , Johannes Weiner , Shakeel Butt , John Dias , Joel Fernandes , sj38.park@gmail.com, alexander.h.duyck@linux.intel.com, Jann Horn Content-Type: text/plain; charset="UTF-8" Sender: linux-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Sun, Mar 1, 2020 at 11:33 PM Oleksandr Natalenko wrote: > > Hello. > > On Fri, Feb 28, 2020 at 03:19:55PM -0800, Suren Baghdasaryan wrote: > > On Tue, Feb 18, 2020 at 5:44 PM Minchan Kim wrote: > > > > > > From: Oleksandr Natalenko > > > > > > Do the very same trick as we already do since 04f5866e41fb. KSM hints > > > will require locking mmap_sem for write since they modify vm_flags, so > > > for remote KSM hinting this additional check is needed. > > > > > > Signed-off-by: Oleksandr Natalenko > > > Signed-off-by: Minchan Kim > > > --- > > > mm/madvise.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/mm/madvise.c b/mm/madvise.c > > > index f6d9b9e66243..c55a18fe71f9 100644 > > > --- a/mm/madvise.c > > > +++ b/mm/madvise.c > > > @@ -1118,6 +1118,8 @@ int do_madvise(struct task_struct *target_task, struct mm_struct *mm, > > > if (write) { > > > if (down_write_killable(&mm->mmap_sem)) > > > return -EINTR; > > > + if (current->mm != mm && !mmget_still_valid(mm)) > > > > mmget_still_valid() seems pretty light-weight, so why not just use > > that without checking that the mm belongs to the current process > > first? > > I'd keep the checks separate to a) do not functionally change current->mm > == mm case; b) clearly separate the intention to call > mmget_still_valid() only for remote access (using mmget_still_valid() > for current->mm == mm does not make any sense here, IMO, since there's > no possibility of expecting a core dump at this point); c) ease the job for > reviewer once mmget_still_valid() is scheduled to be removed (I hope it > eventually goes away indeed). > Makes sense. Thanks! > > > > > + goto skip_mm; > > > } else { > > > down_read(&mm->mmap_sem); > > > } > > > @@ -1169,6 +1171,7 @@ int do_madvise(struct task_struct *target_task, struct mm_struct *mm, > > > } > > > out: > > > blk_finish_plug(&plug); > > > +skip_mm: > > > if (write) > > > up_write(&mm->mmap_sem); > > > else > > > -- > > > 2.25.0.265.gbab2e86ba0-goog > > > > > > > -- > Best regards, > Oleksandr Natalenko (post-factum) > Principal Software Maintenance Engineer > Reviewed-by: Suren Baghdasaryan