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[198.145.29.99]) by mx.google.com with ESMTPS id z11si6829069pgu.306.2019.03.11.23.43.03 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 11 Mar 2019 23:43:03 -0700 (PDT) Received-SPF: pass (google.com: domain of ebiggers@kernel.org designates 198.145.29.99 as permitted sender) client-ip=198.145.29.99; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=AaclTBN2; spf=pass (google.com: domain of ebiggers@kernel.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=ebiggers@kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: from sol.localdomain (c-107-3-167-184.hsd1.ca.comcast.net [107.3.167.184]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7B0D52147C; Tue, 12 Mar 2019 06:43:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1552372982; bh=jxAV6M9Y1tiLlySENmdFKTVIH3Zk5cbYOZ5tGGV6+Q0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=AaclTBN2B/9MbxUhA9MLSSCiEisYs+XLajEA/etj97TINtw4kykiOzEiY1EPoc8j6 wYBigPOZtOTpkJykEee/KzWHKpMreZoBTZJl50r+yN4fJllvh72LA/0yq2XMfaXkg9 /QxxS43KvUtxLh0rftYSHFeG4hFDgiHdrzYJOmJk= Date: Mon, 11 Mar 2019 23:43:01 -0700 From: Eric Biggers To: Andrew Morton , Dmitry Vyukov Cc: syzbot , cgroups@vger.kernel.org, Johannes Weiner , LKML , Linux-MM , Michal Hocko , Michal Hocko , Stephen Rothwell , Shakeel Butt , syzkaller-bugs , Vladimir Davydov Subject: Re: KASAN: null-ptr-deref Read in reclaim_high Message-ID: <20190312064300.GB9123@sol.localdomain> References: <0000000000001fd5780583d1433f@google.com> <20190311163747.f56cceebd9c2661e4519bdfc@linux-foundation.org> <20190311232541.db8571d2e3e0ca636785f31f@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190311232541.db8571d2e3e0ca636785f31f@linux-foundation.org> User-Agent: Mutt/1.11.3 (2019-02-01) 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 Mon, Mar 11, 2019 at 11:25:41PM -0700, Andrew Morton wrote: > On Tue, 12 Mar 2019 07:08:38 +0100 Dmitry Vyukov wrote: > > > On Tue, Mar 12, 2019 at 12:37 AM Andrew Morton > > wrote: > > > > > > On Mon, 11 Mar 2019 06:08:01 -0700 syzbot wrote: > > > > > > > syzbot has bisected this bug to: > > > > > > > > commit 29a4b8e275d1f10c51c7891362877ef6cffae9e7 > > > > Author: Shakeel Butt > > > > Date: Wed Jan 9 22:02:21 2019 +0000 > > > > > > > > memcg: schedule high reclaim for remote memcgs on high_work > > > > > > > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=155bf5db200000 > > > > start commit: 29a4b8e2 memcg: schedule high reclaim for remote memcgs on.. > > > > git tree: linux-next > > > > final crash: https://syzkaller.appspot.com/x/report.txt?x=175bf5db200000 > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=135bf5db200000 > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=611f89e5b6868db > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=fa11f9da42b46cea3b4a > > > > userspace arch: amd64 > > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14259017400000 > > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=141630a0c00000 > > > > > > > > Reported-by: syzbot+fa11f9da42b46cea3b4a@syzkaller.appspotmail.com > > > > Fixes: 29a4b8e2 ("memcg: schedule high reclaim for remote memcgs on > > > > high_work") > > > > > > The following patch > > > memcg-schedule-high-reclaim-for-remote-memcgs-on-high_work-v3.patch > > > might have fixed this. Was it applied? > > > > Hi Andrew, > > > > You mean if the patch was applied during the bisection? > > No, it wasn't. Bisection is very specifically done on the same tree > > where the bug was hit. There are already too many factors that make > > the result flaky/wrong/inconclusive without changing the tree state. > > Now, if syzbot would know about any pending fix for this bug, then it > > would not do the bisection at all. But it have not seen any patch in > > upstream/linux-next with the Reported-by tag, nor it received any syz > > fix commands for this bugs. Should have been it aware of the fix? How? > > memcg-schedule-high-reclaim-for-remote-memcgs-on-high_work-v3.patch was > added to linux-next on Jan 10. I take it that this bug was hit when > testing the entire linux-next tree, so we can assume that > memcg-schedule-high-reclaim-for-remote-memcgs-on-high_work-v3.patch > does not fix it, correct? > > In which case, over to Shakeel! > I don't understand what happened here. First, the syzbot report doesn't say which linux-next version was tested (which it should), but I get: $ git tag --contains 29a4b8e275d1f10c51c7891362877ef6cffae9e7 next-20190110 next-20190111 next-20190114 next-20190115 next-20190116 That's almost 2 months old, yet this bug was just reported now. Why? - Eric