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AJvYcCU2iUktJaD+T8YEV7GT+KA8CUZ5qW7W7rDbE1OY88Z4KbIZkbf/DyBO11lZsalGaQOd92jKmhJUyw==@kvack.org X-Gm-Message-State: AOJu0Yz2zuX6HMR/cf5DQxUmcYTFE5jJufcdEs3mTvFanzZ7c6I6fc4O +zYr7dBcYxoWxGVSQMcD0v6TzSROouU+QK5PIyGLEiwZcoIMfpNRsA7HNzxelJgvAF0xN/Shrx+ /MUsZwm+rIcexCKlUwLPPfNimR+506J6eKNTI X-Google-Smtp-Source: AGHT+IF5RsxrkU7RnBDrWCERFHp/phaVhnDnjzEPKD1Zfn0ZTcAn+P8iVv9SsYXnTvR1ARVmNpRkdcYvTanyF6RTtt8= X-Received: by 2002:a17:90b:2f03:b0:2e2:8995:dd1b with SMTP id 98e67ed59e1d1-2e93c1591e5mr8521696a91.3.1730462979114; Fri, 01 Nov 2024 05:09:39 -0700 (PDT) MIME-Version: 1.0 References: <6723b31e.050a0220.35b515.0165.GAE@google.com> <2928b6e8-3928-411d-82b8-6b17be266deb@lucifer.local> <2023ed50-9aa4-4bc9-8283-82a84c55bc36@lucifer.local> In-Reply-To: <2023ed50-9aa4-4bc9-8283-82a84c55bc36@lucifer.local> From: Aleksandr Nogikh Date: Fri, 1 Nov 2024 13:09:24 +0100 Message-ID: Subject: Re: [syzbot] [mm?] [input?] [usb?] INFO: rcu detected stall in brk (2) To: Lorenzo Stoakes Cc: syzbot , akpm@linux-foundation.org, jannh@google.com, liam.howlett@oracle.com, linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-usb@vger.kernel.org, syzkaller-bugs@googlegroups.com, vbabka@suse.cz, Alan Stern , Dmitry Vyukov Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Queue-Id: 33F6F40026 X-Rspamd-Server: rspam01 X-Stat-Signature: 8yh5k5s83rx5te3t7gnpbxj8w7fgg865 X-HE-Tag: 1730462940-927516 X-HE-Meta: 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 5ZozRLBC 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 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: List-Subscribe: List-Unsubscribe: On Fri, Nov 1, 2024 at 12:11=E2=80=AFPM Lorenzo Stoakes wrote: > > On Fri, Nov 01, 2024 at 12:02:25PM +0100, Aleksandr Nogikh wrote: > > Hi Lorenzo, > > > > On Thu, Oct 31, 2024 at 5:59=E2=80=AFPM 'Lorenzo Stoakes' via syzkaller= -bugs > > wrote: > > > > > > +Alan re: USB stalls > > > > > > On Thu, Oct 31, 2024 at 09:41:02AM -0700, syzbot wrote: > > > > Hello, > > > > > > > > syzbot has tested the proposed patch and the reproducer did not tri= gger any issue: > > > > > > > > Reported-by: syzbot+7402e6c8042635c93ead@syzkaller.appspotmail.com > > > > Tested-by: syzbot+7402e6c8042635c93ead@syzkaller.appspotmail.com > > > > > > > > Tested on: > > > > > > > > commit: cffcc47b mm/mlock: set the correct prev on failure > > > > git tree: git://git.kernel.org/pub/scm/linux/kernel/git/akpm/= mm.git/ mm-hotfixes-unstable > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=3D1304a63= 0580000 > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=3D6648774= f7c39d413 > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=3D7402e6c80= 42635c93ead > > > > compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils= for Debian) 2.40 > > > > > > > > Note: no patches were applied. > > > > Note: testing is done by a robot and is best-effort only. > > > > > > OK this seems likely to be intermittant (and unrelated to what's in > > > mm-unstable-fixes honestly) and does make me wonder if the fix refere= nced > > > in [0] really has sorted things out? Or whether it has perhaps help > > > mitigate the issue but not sufficiently in conjunction with debug thi= ngs > > > that slow things down. > > > > > > Because we keep getting these reports, that mysteriously don't occur = if we > > > re-run (or hit other code paths), they seem to hit somewhat arbitrary= parts > > > of mm, and because CONFIG_DEBUG_VM_MAPLE_TREE is set we spend a _long= _ time > > > in mm validating trees (this config option is REALLY REALLY heavy-han= ded). > > > > > > I note we also set CONFIG_KCOV and CONFIG_KCOV_INSTRUMENT_ALL which i= sn't > > > going to make anything quicker if the USB gets laggy. > > > > These are necessary for coverage-guided fuzzing. Though when we find > > and run reproducers, we don't actually set up /dev/kcov, so I guess > > the impact of coverage callbacks here is not that significant here. > > CONFIG_KASAN is likely slowing down things much more. > > > > > > > > I'm not sure if there's a human who can help tweak the config for the= se > > > hardware-centric tests at Google? At least tweaking the RCU stall tim= e > > > anyway? > > > > We currently set: > > > > CONFIG_RCU_CPU_STALL_TIMEOUT=3D100 > > CONFIG_RCU_EXP_CPU_STALL_TIMEOUT=3D21000 > > > > The expedited RCU timeout was limited to 21 seconds up to some time > > ago, but I guess now we can safely increase this number as well. I'll > > send a PR with syzbot config updates. > > Ah thanks, just sent a reply immediately prior to receiving this :) > > Maybe worth setting CONFIG_RCU_EXP_CPU_STALL_TIMEOUT to 0 so it matches t= he CPU > stall timeout? At least for builds that also set heavy debug options like > CONFIG_DEBUG_VM_MAPLE_TREE? Oh, that's even simpler than I thought it would be, thank you! I've sent https://github.com/google/syzkaller/pull/5455, it will come into effect in a few days. --=20 Aleksandr > > Cheers, Lorenzo > > > > > -- > > Aleksandr > > > > > > > > In any case this continues not to look likely to be an actual mm issu= e as > > > far as I can see. > > > > > > In [0] we were stalled in a validate call which would align with the = idea > > > that perhaps we were just dealing with a very very big tree and getti= ng > > > slow down that way. > > > > > > Cheers, Lorenzo > > > > > > [0]:https://lore.kernel.org/all/967f3aa0-447a-4121-b80b-299c926a33f5@= rowland.harvard.edu/ > > >