From: Florian Weimer <fweimer@redhat.com>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Carlos O'Donell <carlos@redhat.com>,
Joseph Myers <joseph@codesourcery.com>,
Szabolcs Nagy <szabolcs.nagy@arm.com>,
libc-alpha@sourceware.org, Thomas Gleixner <tglx@linutronix.de>,
Ben Maurer <bmaurer@fb.com>,
Peter Zijlstra <peterz@infradead.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Boqun Feng <boqun.feng@gmail.com>,
Will Deacon <will.deacon@arm.com>, Paul Turner <pjt@google.com>,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org
Subject: Re: [PATCH 2/3] Linux: Use rseq in sched_getcpu if available (v9)
Date: Mon, 06 Jul 2020 15:59:35 +0200 [thread overview]
Message-ID: <877dvg4ud4.fsf@oldenburg2.str.redhat.com> (raw)
In-Reply-To: <20200629190036.26982-3-mathieu.desnoyers@efficios.com> (Mathieu Desnoyers's message of "Mon, 29 Jun 2020 15:00:35 -0400")
* Mathieu Desnoyers:
> When available, use the cpu_id field from __rseq_abi on Linux to
> implement sched_getcpu(). Fall-back on the vgetcpu vDSO if
> unavailable.
I've pushed this to glibc master, but unfortunately it looks like this
exposes a kernel bug related to affinity mask changes.
After building and testing glibc, this
for x in {1..2000} ; do posix/tst-affinity-static & done
produces some “error:” lines for me:
error: Unexpected CPU 2, expected 0
error: Unexpected CPU 2, expected 0
error: Unexpected CPU 2, expected 0
error: Unexpected CPU 2, expected 0
error: Unexpected CPU 138, expected 0
error: Unexpected CPU 138, expected 0
error: Unexpected CPU 138, expected 0
error: Unexpected CPU 138, expected 0
“expected 0” is a result of how the test has been written, it bails out
on the first failure, which happens with CPU ID 0.
Smaller systems can use a smaller count than 2000 to reproduce this. It
also happens sporadically when running the glibc test suite itself
(which is why it took further testing to reveal this issue).
I can reproduce this with the Debian 4.19.118-2+deb10u1 kernel, the
Fedora 5.6.19-300.fc32 kernel, and the Red Hat Enterprise Linux kernel
4.18.0-193.el8 (all x86_64).
As to the cause, I'd guess that the exit path in the sched_setaffinity
system call fails to update the rseq area, so that userspace can observe
the outdated CPU ID there.
Thanks,
Florian
next prev parent reply other threads:[~2020-07-06 13:59 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200629190036.26982-1-mathieu.desnoyers@efficios.com>
2020-06-29 19:00 ` [PATCH 1/3] glibc: Perform rseq registration at C startup and thread creation (v22) Mathieu Desnoyers
2020-07-02 14:46 ` Florian Weimer
2020-07-03 17:50 ` Carlos O'Donell
2020-06-29 19:00 ` [PATCH 2/3] Linux: Use rseq in sched_getcpu if available (v9) Mathieu Desnoyers
2020-07-06 13:59 ` Florian Weimer [this message]
2020-07-06 14:49 ` Mathieu Desnoyers
2020-07-06 17:33 ` Mathieu Desnoyers
2020-07-06 17:50 ` Florian Weimer
2020-07-06 18:02 ` Mathieu Desnoyers
2020-07-06 18:11 ` Florian Weimer
2020-07-06 21:08 ` Mathieu Desnoyers
[not found] <20200622180803.1449-1-mathieu.desnoyers@efficios.com>
2020-06-22 18:08 ` Mathieu Desnoyers
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=877dvg4ud4.fsf@oldenburg2.str.redhat.com \
--to=fweimer@redhat.com \
--cc=bmaurer@fb.com \
--cc=boqun.feng@gmail.com \
--cc=carlos@redhat.com \
--cc=joseph@codesourcery.com \
--cc=libc-alpha@sourceware.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=paulmck@linux.vnet.ibm.com \
--cc=peterz@infradead.org \
--cc=pjt@google.com \
--cc=szabolcs.nagy@arm.com \
--cc=tglx@linutronix.de \
--cc=will.deacon@arm.com \
/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).