From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Heiko Carstens <hca@linux.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org, Sven Schnelle <svens@linux.ibm.com>
Subject: Re: __local_bh_enable_ip() vs lockdep
Date: Wed, 16 Dec 2020 18:52:59 +0100 [thread overview]
Message-ID: <20201216175259.GP3040@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20201215144724.40ab7612@gandalf.local.home>
On Tue, Dec 15, 2020 at 02:47:24PM -0500, Steven Rostedt wrote:
> On Tue, 15 Dec 2020 20:01:52 +0100
> Heiko Carstens <hca@linux.ibm.com> wrote:
>
> > Hello,
> >
> > the ftrace stack tracer kernel selftest is able to trigger the warning
> > below from time to time. This looks like there is an ordering problem
> > in __local_bh_enable_ip():
> > first there is a call to lockdep_softirqs_on() and afterwards
> > preempt_count_sub() is ftraced before it was able to modify
> > preempt_count:
>
> Don't run ftrace stack tracer when debugging lockdep. ;-)
>
> /me runs!
Ha!, seriously though; that seems like something we've encountered
before, but my google-fu is failing me.
Do you remember what, if anything, was the problem with this?
---
diff --git a/kernel/softirq.c b/kernel/softirq.c
index d5bfd5e661fc..9d71046ea247 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -186,7 +186,7 @@ void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
* Keep preemption disabled until we are done with
* softirq processing:
*/
- preempt_count_sub(cnt - 1);
+ __preempt_count_sub(cnt - 1);
if (unlikely(!in_interrupt() && local_softirq_pending())) {
/*
next prev parent reply other threads:[~2020-12-16 17:53 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-15 19:01 __local_bh_enable_ip() vs lockdep Heiko Carstens
2020-12-15 19:47 ` Steven Rostedt
2020-12-16 17:52 ` Peter Zijlstra [this message]
2020-12-16 18:35 ` Heiko Carstens
2020-12-18 15:33 ` Heiko Carstens
2020-12-18 15:37 ` Peter Zijlstra
2020-12-18 15:45 ` Peter Zijlstra
2020-12-18 16:02 ` [tip: locking/urgent] softirq: Avoid bad tracing / lockdep interaction tip-bot2 for Peter Zijlstra
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