linux-kernel - Re: [Resend PATCH v2] tracing: Disable interrupt or preemption before acquiring arch_spinlock

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Date:   Tue, 27 Sep 2022 13:12:21 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [Resend PATCH v2] tracing: Disable interrupt or preemption
 before acquiring arch_spinlock_t

On Tue, 27 Sep 2022 11:28:13 -0400
Waiman Long <longman@...hat.com> wrote:

> On 9/22/22 10:56, Waiman Long wrote:
> > It was found that some tracing functions in kernel/trace/trace.c acquire
> > an arch_spinlock_t with preemption and irqs enabled. An example is the
> > tracing_saved_cmdlines_size_read() function which intermittently causes
> > a "BUG: using smp_processor_id() in preemptible" warning when the LTP
> > read_all_proc test is run.
> >
> > That can be problematic in case preemption happens after acquiring the
> > lock. Add the necessary preemption or interrupt disabling code in the
> > appropriate places before acquiring an arch_spinlock_t.
> >
> > The convention here is to disable preemption for trace_cmdline_lock and
> > interupt for max_lock.
> >
> > Fixes: a35873a0993b ("tracing: Add conditional snapshot")
> > Fixes: 939c7a4f04fc ("tracing: Introduce saved_cmdlines_size file")
> > Suggested-by: Steven Rostedt <rostedt@...dmis.org>
> > Signed-off-by: Waiman Long <longman@...hat.com>
> > ---
> >   kernel/trace/trace.c | 23 +++++++++++++++++++++++
> >   1 file changed, 23 insertions(+)  
> 
> Ping!
> 
> Any comment on this patch?

You may have noticed (from today's emailing) I applied the patch ;-)

-- Steve