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Fri, 17 Sep 2021 00:32:26 -0700 (PDT) MIME-Version: 1.0 References: <000000000000ce4c9505bdd4a48f@google.com> <20210325182046.GA15860@willie-the-truck> <20210325191006.GE15860@willie-the-truck> <20210325192918.GB16123@willie-the-truck> In-Reply-To: <20210325192918.GB16123@willie-the-truck> From: Dmitry Vyukov Date: Fri, 17 Sep 2021 09:32:16 +0200 Message-ID: Subject: Re: [syzbot] BUG: soft lockup in do_wp_page (4) To: Will Deacon Cc: syzbot , kernel-team@android.com, Andrew Morton , LKML , Linux-MM , syzkaller-bugs , Linux ARM , syzkaller Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: B1162B0000A3 X-Stat-Signature: thkxzi5jfogu8obtuhyrpeosmk397cjf Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=f659RD4A; spf=pass (imf19.hostedemail.com: domain of dvyukov@google.com designates 209.85.167.182 as permitted sender) smtp.mailfrom=dvyukov@google.com; dmarc=pass (policy=reject) header.from=google.com X-HE-Tag: 1631863947-227978 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 Thu, 25 Mar 2021 at 20:29, Will Deacon wrote: > > On Thu, Mar 25, 2021 at 08:24:53PM +0100, Dmitry Vyukov wrote: > > On Thu, Mar 25, 2021 at 8:10 PM Will Deacon wrote: > > > On Thu, Mar 25, 2021 at 07:34:54PM +0100, Dmitry Vyukov wrote: > > > > On Thu, Mar 25, 2021 at 7:20 PM Will Deacon wrote: > > > > > On Thu, Mar 18, 2021 at 08:34:16PM +0100, Dmitry Vyukov wrote: > > > > > > On Thu, Mar 18, 2021 at 8:31 PM syzbot > > > > > > wrote: > > > > > > commit cae118b6acc309539b33339e846cbb19187c164c > > > > > > Author: Will Deacon > > > > > > Date: Wed Mar 3 13:49:27 2021 +0000 > > > > > > arm64: Drop support for CMDLINE_EXTEND > > > > > > > > > > > > syzbot passes lots of critical things in CONFIG_CMDLINE: > > > > > > https://github.com/google/syzkaller/blob/c3c81c94865791469d376eba84f4a2d7763d3f71/dashboard/config/linux/upstream-arm64-kasan.config#L495 > > > > > > but also wants the bootloader args to be appended. > > > > > > What is the way to do it now? > > > > > > > > > > For now, there isn't a way to do it with CONFIG_CMDLINE, so I think you can > > > > > either: > > > > > > > > > > * Revert my patch for your kernels > > > > > * Pass the arguments via QEMU's -append option > > > > > * Take a look at one of the series which should hopefully add this > > > > > functionality back (but with well-defined semantics) [1] [2] > > > > > > > > Unfortunately none of these work for syzbot (and I assume other > > > > testing environments). > > > > > > > > syzbot does not support custom patches by design: > > > > http://bit.do/syzbot#no-custom-patches > > > > As any testing system, it tests the official trees. > > > > > > > > It's not humans who start these VMs, so it's not as easy as changing > > > > the command line after typing... > > > > There is no support for passing args specifically to qemu, syzkaller > > > > support not just qemu, so these things are specifically localized in > > > > the config. Additionally there is an issue of communicating all these > > > > scattered details to developers in bug reports. Currently syzbot > > > > reports the kernel config and it as well captures command line. > > > > > > > > Could you revert the patch? Is there any point in removing the > > > > currently supported feature before the new feature lands? > > > > > > Well, we only just merged it (in 5.10 I think?), and the semantics of the > > > new version will be different, so I really don't see the value in supporting > > > both (even worse, Android has its own implementation which is different > > > again). The timeline was: we merged CMDLINE_EXTEND, then we noticed it was > > > broken, my fixes were rejected, so we removed the feature rather than > > > support the broken version. In the relatively small window while it was > > > merged, syzbot started using it :( > > > > I didn't realize it was just introduced :) > > We used CMDLINE_EXTEND on x86, and I looked for a similar option for > > arm64 and found it. > > > > > So I really think the best bet is to wait until the patches are sorted out. > > > I think Christophe is about to spin a new version, and I reviewed his last > > > copy, so I don't see this being far off, > > > > If it's expected to be merged soon, let's wait. > > Thanks, and knowing that we have a keen user helps to prioritise the review > :) Any updates on proper CMDLINE support for arm64? This is still broken for syzbot and it periodically reports false positives due to incorrect cmdline.