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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id e17sm1939961qtw.1.2020.04.10.07.26.24 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 10 Apr 2020 07:26:24 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.80.23.2.2\)) Subject: Re: [PATCH 0/2] mm: Two small fixes for recent syzbot reports From: Qian Cai In-Reply-To: <76e8bbed-21d1-22e1-4148-5a5766652c0d@I-love.SAKURA.ne.jp> Date: Fri, 10 Apr 2020 10:26:23 -0400 Cc: Dmitry Vyukov , Linus Torvalds , Stephen Rothwell , Andrew Morton , Peter Xu , LKML , Linux-MM Content-Transfer-Encoding: quoted-printable Message-Id: <22DAFAC7-9F39-4042-BC79-B27963A13E3D@lca.pw> References: <9C21961E-24D3-4C97-A5AB-B70451E4F952@lca.pw> <76e8bbed-21d1-22e1-4148-5a5766652c0d@I-love.SAKURA.ne.jp> To: Tetsuo Handa X-Mailer: Apple Mail (2.3608.80.23.2.2) 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 Apr 10, 2020, at 9:12 AM, Tetsuo Handa = wrote: >=20 > On 2020/04/10 6:14, Qian Cai wrote: >>=20 >>=20 >>> On Apr 9, 2020, at 2:06 PM, Linus Torvalds = wrote: >>>=20 >>> On Thu, Apr 9, 2020 at 10:58 AM Qian Cai wrote: >>>>=20 >>>> Agree to make a big deal part. My point is that when kicking trees = of linux-next, it also could reduce the exposure of many patches (which = could be bad) to linux-next and miss valuable early testing either from = robots or human. >>>=20 >>> Sure. But I'd want to be notified when something gets kicked out, so >>> that I then know not to pull it. >>>=20 >>> So it would reduce the exposure of patches, but it would also make >>> sure those patches then don't make it upstream. >>>=20 >>> Untested patches is fine - as long as nobody else has to suffer = through them. >>=20 >> Excellent. It now very much depends on how Stephen will notify you = when >> a tree, a patchset or even a developer should be blacklisted for some = time >> to make this a success. >>=20 >=20 > Since patch flow forms tree structure, I don't know whether = maintainers can > afford remembering which tree, patchset or developer should be = blacklisted > when problems come from leaf git trees. >=20 >=20 >=20 > By the way... >=20 > Removing problematic trees might confuse "#syz test:" request, for > developers might ask syzbot to test proposed patches on a kernel which > does not contain problematic trees. In lucky case, test request fails > as patch failure or build failure. But in unlucky case, syzbot fails = to > detect that proposed patch was tested on a kernel without problematic > trees. A bit related to = https://github.com/google/syzkaller/issues/1609 . >=20 I looked at those blocking bug list sent by Dmitry. I wonder =E2=80=9Cboys= , why they did=E2=80=99t send those out earlier to linux-next or somewhere more = visible?=E2=80=9D because I had dealt with most of those before, and I knew the solutions to = unblock them! Even though my testing setup is somewhat different from syzbot. I = don=E2=80=99t do fuzzers, and my config is only focus on mm, iommu and a few core kernel = pieces with more debugging options on, but it does bare-metal and multi-arch, = there are still lots of opportunities to help each other with dealing with = blocking issues. A few things I am doing differently with syzbot on linux-next where = would help to be run continuous without blocking most of the time are, I don=E2=80=99t set panic_on_warn. I=E2=80=99ll deal with warnings = afterwards. Occasionally, there are hard failures that I have to deal with right = now. I=E2=80=99ll get to the end of it, and figured out the exact commit caused it. In syzbot mode, the bisection (by robot) is the hard part, because if = you don=E2=80=99t figure out the exact commit, most of times people (CC by the bug = reports) would have no clue and will be ignored. (even if the bad commit was figured = out, it is not 100% guaranteed developers would know what=E2=80=99s going on but it = helps dramatically, and at least we can revert it without blocking if = everything else fails). Thus, it would be really help if syzbot (or human operators) could help = bisect, even if it could only figure out one of merge commit in linux-next is bad = (where with high accuracy) and may get those ignored less.=