linux-kernel - Re: BUG: using __this_cpu_read() in preemptible code in trace_hardirqs

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Message-ID: <20201022163247.5bb93ab3@gandalf.local.home>
Date:   Thu, 22 Oct 2020 16:32:47 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     syzbot <syzbot+53f8ce8bbc07924b6417@...kaller.appspotmail.com>,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: BUG: using __this_cpu_read() in preemptible code in
 trace_hardirqs_on

On Thu, 22 Oct 2020 12:30:28 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> Subject: lockdep: Fix preemption WARN for spurious IRQ-enable
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Thu Oct 22 12:23:02 CEST 2020
> 
> It is valid (albeit uncommon) to call local_irq_enable() without first
> having called local_irq_disable(). In this case we enter
> lockdep_hardirqs_on*() with IRQs enabled and trip a preemption warning
> for using __this_cpu_read().
> 
> Use this_cpu_read() instead to avoid the warning.

I was wondering why you were using __this_cpu_read() in the first place.

Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve


> 
> Fixes: 4d004099a6 ("lockdep: Fix lockdep recursion")
> Reported-by: syzbot+53f8ce8bbc07924b6417@...kaller.appspotmail.com
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>