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[209.85.220.65]) by mx.google.com with SMTPS id i1sor538160wmb.11.2019.02.07.16.28.37 for (Google Transport Security); Thu, 07 Feb 2019 16:28:37 -0800 (PST) Received-SPF: pass (google.com: domain of andrea.parri@amarulasolutions.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@amarulasolutions.com header.s=google header.b=D67VAcZg; spf=pass (google.com: domain of andrea.parri@amarulasolutions.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=andrea.parri@amarulasolutions.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amarulasolutions.com; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=TFpCruOEkYxlPOvEEM4WFb5ey4gGwCCM6JNzhOMWsYE=; b=D67VAcZg3uDP0lt9Sqg3MIsMeyXF/IH/FyGFwTyCK9FBdMzZcUZ/IEInD3OWp8WxIC WEVgcce2X8YCEDWht3MGxN0hhnRiDp/ybXUoyenVwtWaQ8Ej36yQNGKDNTmUnP3XLmo5 Pf2D+6vx6zZug8M9Bnfd8AMx+hd9KrPLV1IY0= X-Google-Smtp-Source: AHgI3Ib1IgqbTuJHNdOcNnbDtuMtaOd+O86FOmXBYiUksPi/GJs8dD1XdmK4O4yj6ekfRFBRqwpfDA== X-Received: by 2002:a1c:6c14:: with SMTP id h20mr521880wmc.78.1549585717124; Thu, 07 Feb 2019 16:28:37 -0800 (PST) Received: from andrea ([89.22.71.151]) by smtp.gmail.com with ESMTPSA id w16sm464450wrp.1.2019.02.07.16.28.35 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 07 Feb 2019 16:28:36 -0800 (PST) Date: Fri, 8 Feb 2019 01:28:29 +0100 From: Andrea Parri To: Hugh Dickins Cc: Andrew Morton , "Huang, Ying" , Daniel Jordan , dan.carpenter@oracle.com, dave.hansen@linux.intel.com, sfr@canb.auug.org.au, osandov@fb.com, tj@kernel.org, ak@linux.intel.com, linux-mm@kvack.org, kernel-janitors@vger.kernel.org, paulmck@linux.ibm.com, stern@rowland.harvard.edu, peterz@infradead.org, willy@infradead.org, will.deacon@arm.com Subject: Re: About swapoff race patch (was Re: [PATCH] mm, swap: bounds check swap_info accesses to avoid NULL derefs) Message-ID: <20190207234244.GA6429@andrea> References: <20190114222529.43zay6r242ipw5jb@ca-dmjordan1.us.oracle.com> <20190115002305.15402-1-daniel.m.jordan@oracle.com> <20190129222622.440a6c3af63c57f0aa5c09ca@linux-foundation.org> <87tvhpy22q.fsf_-_@yhuang-dev.intel.com> <20190131124655.96af1eb7e2f7bb0905527872@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) 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: Hi Huang, Ying, On Mon, Feb 04, 2019 at 01:37:00PM -0800, Hugh Dickins wrote: > On Thu, 31 Jan 2019, Andrew Morton wrote: > > On Thu, 31 Jan 2019 10:48:29 +0800 "Huang\, Ying" wrote: > > > Andrew Morton writes: > > > > mm-swap-fix-race-between-swapoff-and-some-swap-operations.patch is very > > > > stuck so can you please redo this against mainline? > > > > > > Allow me to be off topic, this patch has been in mm tree for quite some > > > time, what can I do to help this be merged upstream? [...] > > Wow, yes, it's about a year old. > > > > > I have no evidence that it has been reviewed, for a start. I've asked > > Hugh to look at it. > > I tried at the weekend. Usual story: I don't like it at all, the > ever-increasing complexity there, but certainly understand the need > for that fix, and have not managed to think up anything better - > and now I need to switch away, sorry. FWIW, I do agree with Hugh about "the need for that fix": AFAIU, that (mainline) code is naively buggy _and_ "this patch": http://lkml.kernel.org/r/20180223060010.954-1-ying.huang@intel.com "redone on top of mainline" seems both correct and appropriate to me. > (I was originally horrified by the stop_machine() added in swapon and > swapoff, but perhaps I'm remembering a distant past of really stopping > the machine: stop_machine() today looked reasonable, something to avoid > generally like lru_add_drain_all(), but not as shameful as I thought.) AFAIC_find_on_LKML, we have three different fixes (at least!): resp., 1. refcount(-based), 2. RCU, 3. stop_machine(); (3) appears to be the less documented/relied-upon/tested among these; I'm not aware of definitive reasons forcing us to reject (1) and (2). Andrea > > Hugh