linux-kernel - Re: [WARNING] kernel/rcu/tree.c:1058 rcu_irq

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Message-ID: <20201002181313.GM29142@worktop.programming.kicks-ass.net>
Date:   Fri, 2 Oct 2020 20:13:13 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [WARNING] kernel/rcu/tree.c:1058 rcu_irq_enter+0x15/0x20

On Fri, Oct 02, 2020 at 01:56:44PM -0400, Steven Rostedt wrote:
> On Wed, 30 Sep 2020 20:13:23 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > Blergh, IIRC there's header hell that way. The sane fix is killing off
> > that trace_*_rcuidle() disease.
> > 
> > But I think this will also cure it.
> 
> I guess you still don't build modules ;-). I had to add a
> EXPORT_SYMBOL(lockdep_recursion) to get it to build, and then move the

Correct, my regular configs are all without modules.

> checks within the irq disabling to get rid of the using cpu pointers within
> preemptable code warnings

Ah, I think I lost a s/__this_cpu_read/raw_cpu_read/ somewhere. The
thing is, if we're preemptible/migratable it will be 0 on both CPUs and
it doesn't matter which 0 we read. If it is !0, IRQs will be disabled
and we can't get migrated.

Anyway, let me go write a Changelog to go with it.