From: Sven Schnelle <svens@linux.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: hca@linux.ibm.com, linux-kernel@vger.kernel.org,
linux-s390@vger.kernel.org, rafael.j.wysocki@intel.com
Subject: Re: [PATCH] s390/idle: Fix suspicious RCU usage
Date: Thu, 08 Oct 2020 10:58:05 +0200 [thread overview]
Message-ID: <yt9dy2khrt5u.fsf@linux.ibm.com> (raw)
In-Reply-To: <20201007125625.GK2651@hirez.programming.kicks-ass.net> (Peter Zijlstra's message of "Wed, 7 Oct 2020 14:56:25 +0200")
Hi Peter,
Peter Zijlstra <peterz@infradead.org> writes:
> On Wed, Oct 07, 2020 at 12:05:51PM +0200, Peter Zijlstra wrote:
>> On Wed, Oct 07, 2020 at 09:53:25AM +0200, Sven Schnelle wrote:
>> > Hi Peter,
>> >
>> > peterz@infradead.org writes:
>> >
>> > > After commit eb1f00237aca ("lockdep,trace: Expose tracepoints") the
>> > > lock tracepoints are visible to lockdep and RCU-lockdep is finding a
>> > > bunch more RCU violations that were previously hidden.
>> > >
>> > > Switch the idle->seqcount over to using raw_write_*() to avoid the
>> > > lockdep annotation and thus the lock tracepoints.
>> > >
>> > > Reported-by: Guenter Roeck <linux@roeck-us.net>
>> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>> > > [..]
>> >
>> > I'm still seeing the splat below on s390 when irq tracing is enabled:
>>
>> Damn... :/
>>
>> This one is tricky, trouble seems to be that arch_cpu_idle() is defined
>> to enable interrupts (no doubt because ot x86 :/), but we call it before
>> rcu_exit_idle().
>>
>> What a mess... let me rummage around the various archs to see what makes
>> most sense here.
>
> Maybe something like so, I've not yet tested it. I need to figure out
> how to force x86 into this path.
I've gave this patch a quick test on linux-next from today and haven't
seen the splat again. However it wasn't happening all the time, so will
test it a bit longer. I haven't looked into the tracing code in detail,
but i guess it was only happening when the lock was contented.
The only thing with this patch is that rcu complains that it gets called
with interrupts enabled on s390 when rcu_irq_enter() is called. But a
few trace_hardirqs_{on,off} at the beginning and end of the IRQ handlers
are fixing this. Will check why this worked in the past.
Sven
prev parent reply other threads:[~2020-10-08 8:58 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-08 13:30 [PATCH] s390/idle: Fix suspicious RCU usage peterz
2020-09-08 13:41 ` Heiko Carstens
2020-10-07 7:53 ` Sven Schnelle
2020-10-07 10:05 ` Peter Zijlstra
2020-10-07 12:56 ` Peter Zijlstra
2020-10-08 8:58 ` Sven Schnelle [this message]
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=yt9dy2khrt5u.fsf@linux.ibm.com \
--to=svens@linux.ibm.com \
--cc=hca@linux.ibm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-s390@vger.kernel.org \
--cc=peterz@infradead.org \
--cc=rafael.j.wysocki@intel.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).