From: Peter Zijlstra <peterz@infradead.org>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>,
Theodore Ts'o <tytso@mit.edu>,
syzbot <syzbot+4bfbbf28a2e50ab07368@syzkaller.appspotmail.com>,
Andreas Dilger <adilger.kernel@dilger.ca>,
David Miller <davem@davemloft.net>,
eladr@mellanox.com, Ido Schimmel <idosch@mellanox.com>,
Jiri Pirko <jiri@mellanox.com>,
John Stultz <john.stultz@linaro.org>,
linux-ext4@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
netdev <netdev@vger.kernel.org>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>
Subject: Re: INFO: rcu detected stall in ext4_write_checks
Date: Mon, 15 Jul 2019 15:46:51 +0200 [thread overview]
Message-ID: <20190715134651.GI3419@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CACT4Y+bmgdOExBHnLJ+jgWKWQzNK9CFT6_eTxFE3hoK=0YresQ@mail.gmail.com>
On Mon, Jul 15, 2019 at 03:33:11PM +0200, Dmitry Vyukov wrote:
> On Mon, Jul 15, 2019 at 3:29 PM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Sun, Jul 14, 2019 at 11:49:15AM -0700, Paul E. McKenney wrote:
> > > On Sun, Jul 14, 2019 at 05:48:00PM +0300, Dmitry Vyukov wrote:
> > > > But short term I don't see any other solution than stop testing
> > > > sched_setattr because it does not check arguments enough to prevent
> > > > system misbehavior. Which is a pity because syzkaller has found some
> > > > bad misconfigurations that were oversight on checking side.
> > > > Any other suggestions?
> > >
> > > Keep the times down to a few seconds? Of course, that might also
> > > fail to find interesting bugs.
> >
> > Right, if syzcaller can put a limit on the period/deadline parameters
> > (and make sure to not write "-1" to
> > /proc/sys/kernel/sched_rt_runtime_us) then per the in-kernel
> > access-control should not allow these things to happen.
>
> Since we are racing with emails, could you suggest a 100% safe
> parameters? Because I only hear people saying "safe", "sane",
> "well-behaving" :)
> If we move the check to user-space, it does not mean that we can get
> away without actually defining what that means.
Right, well, that's part of the problem. I think Paul just did the
reverse math and figured that 95% of X must not be larger than my
watchdog timeout and landed on 14 seconds.
I'm thinking 4 seconds (or rather 4.294967296) would be a very nice
number.
> Now thinking of this, if we come up with some simple criteria, could
> we have something like a sysctl that would allow only really "safe"
> parameters?
I suppose we could do that, something like:
sysctl_deadline_period_{min,max}. I'll have to dig back a bit on where
we last talked about that and what the problems where.
For one, setting the min is a lot harder, but I suppose we can start at
TICK_NSEC or something.
next prev parent reply other threads:[~2019-07-15 13:47 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-26 17:27 INFO: rcu detected stall in ext4_write_checks syzbot
2019-06-26 18:42 ` Theodore Ts'o
2019-06-26 21:03 ` Theodore Ts'o
2019-06-26 22:47 ` Theodore Ts'o
2019-07-05 13:24 ` Dmitry Vyukov
2019-07-05 15:16 ` Paul E. McKenney
2019-07-05 15:47 ` Amir Goldstein
2019-07-05 15:48 ` Dmitry Vyukov
2019-07-05 19:10 ` Paul E. McKenney
2019-07-06 4:28 ` Theodore Ts'o
2019-07-06 6:16 ` Paul E. McKenney
2019-07-06 15:02 ` Theodore Ts'o
2019-07-06 18:03 ` Paul E. McKenney
2019-07-07 1:16 ` Paul E. McKenney
2019-07-14 14:48 ` Dmitry Vyukov
2019-07-14 18:49 ` Paul E. McKenney
2019-07-15 13:29 ` Peter Zijlstra
2019-07-15 13:33 ` Dmitry Vyukov
2019-07-15 13:46 ` Peter Zijlstra [this message]
2019-07-15 14:02 ` Paul E. McKenney
2019-07-22 10:03 ` Dmitry Vyukov
2019-07-23 8:51 ` Dmitry Vyukov
2019-07-14 19:05 ` Theodore Ts'o
2019-07-14 19:29 ` Paul E. McKenney
2019-07-15 3:10 ` Paul E. McKenney
2019-07-15 13:01 ` Paul E. McKenney
2019-07-15 13:29 ` Dmitry Vyukov
2019-07-15 13:39 ` Peter Zijlstra
2019-07-15 14:03 ` Paul E. McKenney
2019-07-15 13:22 ` Peter Zijlstra
2019-07-05 13:18 ` Dmitry Vyukov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190715134651.GI3419@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=adilger.kernel@dilger.ca \
--cc=davem@davemloft.net \
--cc=dvyukov@google.com \
--cc=eladr@mellanox.com \
--cc=idosch@mellanox.com \
--cc=jiri@mellanox.com \
--cc=john.stultz@linaro.org \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=netdev@vger.kernel.org \
--cc=paulmck@linux.ibm.com \
--cc=syzbot+4bfbbf28a2e50ab07368@syzkaller.appspotmail.com \
--cc=syzkaller-bugs@googlegroups.com \
--cc=tglx@linutronix.de \
--cc=tytso@mit.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).