From: "Theodore Ts'o" <tytso@mit.edu>
To: syzbot <syzbot+4bfbbf28a2e50ab07368@syzkaller.appspotmail.com>,
adilger.kernel@dilger.ca, davem@davemloft.net,
eladr@mellanox.com, idosch@mellanox.com, jiri@mellanox.com,
john.stultz@linaro.org, linux-ext4@vger.kernel.org,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
syzkaller-bugs@googlegroups.com, tglx@linutronix.de
Subject: Re: INFO: rcu detected stall in ext4_write_checks
Date: Wed, 26 Jun 2019 18:47:09 -0400 [thread overview]
Message-ID: <20190626224709.GH3116@mit.edu> (raw)
In-Reply-To: <20190626210351.GF3116@mit.edu>
More details about what is going on. First, it requires root, because
one of that is required is using sched_setattr (which is enough to
shoot yourself in the foot):
sched_setattr(0, {size=0, sched_policy=0x6 /* SCHED_??? */, sched_flags=0, sched_nice=0, sched_priority=0, sched_runtime=2251799813724439, sched_deadline=4611686018427453437, sched_period=0}, 0) = 0
This is setting the scheduler policy to be SCHED_DEADLINE, with a
runtime parameter of 2251799.813724439 seconds (or 26 days) and a
deadline of 4611686018.427453437 seconds (or 146 *years*). This means
a particular kernel thread can run for up to 26 **days** before it is
scheduled away, and if a kernel reads gets woken up or sent a signal,
no worries, it will wake up roughly seven times the interval that Rip
Van Winkle spent snoozing in a cave in the Catskill Mountains (in
Washington Irving's short story).
We then kick off a half-dozen threads all running:
sendfile(fd, fd, &pos, 0x8080fffffffe);
(and since count is a ridiculously large number, this gets cut down to):
sendfile(fd, fd, &pos, 2147479552);
Is it any wonder that we are seeing RCU stalls? :-)
- Ted
next prev parent reply other threads:[~2019-06-26 22:47 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 [this message]
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
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=20190626224709.GH3116@mit.edu \
--to=tytso@mit.edu \
--cc=adilger.kernel@dilger.ca \
--cc=davem@davemloft.net \
--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=netdev@vger.kernel.org \
--cc=syzbot+4bfbbf28a2e50ab07368@syzkaller.appspotmail.com \
--cc=syzkaller-bugs@googlegroups.com \
--cc=tglx@linutronix.de \
/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).