From owner-svn-src-all@freebsd.org Fri Jul 10 08:37:35 2020
Return-Path: <owner-svn-src-all@freebsd.org>
Delivered-To: svn-src-all@mailman.nyi.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1])
by mailman.nyi.freebsd.org (Postfix) with ESMTP id DAF9E363CD5;
Fri, 10 Jul 2020 08:37:35 +0000 (UTC)
(envelope-from mjguzik@gmail.com)
Received: from mail-wm1-x342.google.com (mail-wm1-x342.google.com
[IPv6:2a00:1450:4864:20::342])
(using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits)
key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256
client-signature RSA-PSS (2048 bits) client-digest SHA256)
(Client CN "smtp.gmail.com", Issuer "GTS CA 1O1" (verified OK))
by mx1.freebsd.org (Postfix) with ESMTPS id 4B35yR1Ktpz4Kqb;
Fri, 10 Jul 2020 08:37:34 +0000 (UTC)
(envelope-from mjguzik@gmail.com)
Received: by mail-wm1-x342.google.com with SMTP id 17so4982177wmo.1;
Fri, 10 Jul 2020 01:37:34 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025;
h=mime-version:in-reply-to:references:from:date:message-id:subject:to
:cc; bh=XdmVb1jcH6gmU+aFH0vi4PmV0BL6UmkArM8sU1ZYUAE=;
b=n+ebrB3U/dl0ArmWHlSxuSpKWJ9QZ/Ars9AIuriYVrrDssM5ZBRWpyswH5FxL4mIya
aMfDes4EKNlT/Qmgnpa7XCmN53prBLgiP5LzS4T97Nns6edwG4HKiJ2nHbCEurpc+k4T
QhsKJiPH7c2LI13f/gyTSyps7DsHYlt9WLCm+JjNIwxD2BaQnD3ro2jgdZwdC2/luqNO
1L0U8qvRHdjHO/E9AqJGL221utDt91K9O+0j11tZQi9Gslz3jjw20eVGXIy/pX+4bOUG
kPf5sVl6pERFhlUzZ6VSwphP4UfhellRB04lJHwE/Xz2UNDGf3UBd2qjAeACPQcRP2G9
w3Hw==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
d=1e100.net; s=20161025;
h=x-gm-message-state:mime-version:in-reply-to:references:from:date
:message-id:subject:to:cc;
bh=XdmVb1jcH6gmU+aFH0vi4PmV0BL6UmkArM8sU1ZYUAE=;
b=XtkBsXxb8UnYXTGOw1HUmACwVpnfZ5pE+TphbwjGQY6Uy2uac0aMtsyTbnbINRWx+8
TbGVPgJ++NUfQVYIh13OEvwwc4KBi5cFEqwkA9TA96+8fxXhaDUznrbVkMxdznEBBNqD
uKm/2zkRqOpN/+OcBMdDoJxuQbUdvDVKQ7acN3cjN5eQ5ZIjJE8CxZGFz39Ea8+1p7Rq
F9T5783c+WUmdRyLopTCLx1ZY1fbDf10levtVmPJLWsVndOEIEW4i+cCe/UDtTVcYh5e
zB7yRLt7yc2ymlhTQ35wUE3a/CLAwDyHC9836weWrNo8bQKZTJ38xdUDnyaGuLvoiinH
xUXw==
X-Gm-Message-State: AOAM533WPTL4QkOh12hgstjw4Qwa4Bdab1vQJf9n/mtOl56iNTiERXjI
5y98DsAZQ+Hp5opXYpIGw31PyF95ZeDTv7uxofywOg==
X-Google-Smtp-Source: ABdhPJwdwv37I+WY6Ca6BDDSUGyIx3BFAC/PIas2DmriFUyTBTpeatHuDg5SZudq23YPvETZK6eYOVAyP1AJ/tP+Kj0=
X-Received: by 2002:a1c:e90d:: with SMTP id q13mr4163326wmc.187.1594370252787;
Fri, 10 Jul 2020 01:37:32 -0700 (PDT)
MIME-Version: 1.0
Received: by 2002:adf:9d84:0:0:0:0:0 with HTTP; Fri, 10 Jul 2020 01:37:32
-0700 (PDT)
In-Reply-To: <CAGudoHFCsJ4PUuM0Xixdf9haCObWz8wdDzx48BEoqJ7=+5u7QA@mail.gmail.com>
References: <202007100646.06A6kgnX015296@repo.freebsd.org>
<20200710082549.GC74062@freefall.freebsd.org>
<CAGudoHFCsJ4PUuM0Xixdf9haCObWz8wdDzx48BEoqJ7=+5u7QA@mail.gmail.com>
From: Mateusz Guzik <mjguzik@gmail.com>
Date: Fri, 10 Jul 2020 10:37:32 +0200
Message-ID: <CAGudoHGE7a9VqDe4RbLCoADp4h42CXe0e1s8F6=ANtdMCmVJRQ@mail.gmail.com>
Subject: Re: svn commit: r363068 - head/sys/kern
To: "Piotr P. Stefaniak" <pstef@freebsd.org>
Cc: src-committers@freebsd.org, svn-src-all@freebsd.org,
svn-src-head@freebsd.org
Content-Type: text/plain; charset="UTF-8"
X-Rspamd-Queue-Id: 4B35yR1Ktpz4Kqb
X-Spamd-Bar: ---
Authentication-Results: mx1.freebsd.org;
dkim=pass header.d=gmail.com header.s=20161025 header.b=n+ebrB3U;
dmarc=pass (policy=none) header.from=gmail.com;
spf=pass (mx1.freebsd.org: domain of mjguzik@gmail.com designates
2a00:1450:4864:20::342 as permitted sender) smtp.mailfrom=mjguzik@gmail.com
X-Spamd-Result: default: False [-3.76 / 15.00]; ARC_NA(0.00)[];
NEURAL_HAM_MEDIUM(-1.00)[-1.001];
R_DKIM_ALLOW(-0.20)[gmail.com:s=20161025]; FROM_HAS_DN(0.00)[];
RCPT_COUNT_THREE(0.00)[4]; FREEMAIL_FROM(0.00)[gmail.com];
TO_MATCH_ENVRCPT_ALL(0.00)[]; MIME_GOOD(-0.10)[text/plain];
R_SPF_ALLOW(-0.20)[+ip6:2a00:1450:4000::/36];
NEURAL_HAM_LONG(-1.04)[-1.037]; TO_DN_SOME(0.00)[];
DKIM_TRACE(0.00)[gmail.com:+];
DMARC_POLICY_ALLOW(-0.50)[gmail.com,none];
RCVD_IN_DNSWL_NONE(0.00)[2a00:1450:4864:20::342:from];
NEURAL_HAM_SHORT(-0.73)[-0.726]; FROM_EQ_ENVFROM(0.00)[];
MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVFROM(0.00)[gmail.com];
ASN(0.00)[asn:15169, ipnet:2a00:1450::/32, country:US];
RCVD_COUNT_TWO(0.00)[2]; RCVD_TLS_ALL(0.00)[];
DWL_DNSWL_NONE(0.00)[gmail.com:dkim]
X-BeenThere: svn-src-all@freebsd.org
X-Mailman-Version: 2.1.33
Precedence: list
List-Id: "SVN commit messages for the entire src tree \(except for "
user" and " projects" \)" <svn-src-all.freebsd.org>
List-Unsubscribe: <https://lists.freebsd.org/mailman/options/svn-src-all>,
<mailto:svn-src-all-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/svn-src-all/>
List-Post: <mailto:svn-src-all@freebsd.org>
List-Help: <mailto:svn-src-all-request@freebsd.org?subject=help>
List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/svn-src-all>,
<mailto:svn-src-all-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 10 Jul 2020 08:37:35 -0000
On 7/10/20, Mateusz Guzik <mjguzik@gmail.com> wrote:
> On 7/10/20, Piotr P. Stefaniak <pstef@freebsd.org> wrote:
>>> */
>>>- memcpy(sbp, &mp->mnt_stat, sizeof(*sbp));
>>>+ if (sbp != &mp->mnt_stat)
>>>+ memcpy(sbp, &mp->mnt_stat, sizeof(*sbp));
>>>
>>
>> Slightly unrelated question: wouldn't it be prudent to incorporate this
>> logic into memcpy?
>>
>
> Calls like that are just abusing the routine and indicate design
> problems in the consumer.
> Adding the branch into the routine would add overhead for everyone.
>
> However, now that you mention it, it may be prudent to do something like
> this:
>
> dtrace -n 'fbt::memcpy:entry,fbt::memmove:entry /arg1 == arg2/ {
> @[stack()] = count(); }'
>
> and run your favourite workload.
>
Oops, that should be:
dtrace -n 'fbt::memcpy:entry,fbt::memmove:entry /arg0 == arg1/ {
@[stack()] = count(); }'
You can look for other abuse too, here are 0-sized calls:
dtrace -n 'fbt::memcpy:entry,fbt::memmove:entry,fbt::memset:entry
/arg2 == 0/ { @[probefunc,stack()] = count(); }'
--
Mateusz Guzik <mjguzik gmail.com>