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Date:   Tue, 27 Sep 2022 13:12:21 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Waiman Long <longman@redhat.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>, linux-kernel@vger.kernel.org
Subject: Re: [Resend PATCH v2] tracing: Disable interrupt or preemption
 before acquiring arch_spinlock_t
Message-ID: <20220927131221.1b3a736b@gandalf.local.home>
In-Reply-To: <9c798af6-aa2c-5f76-7a50-ef1983f9bdcd@redhat.com>
References: <20220922133158.1731333-1-longman@redhat.com>
        <20220922145622.1744826-1-longman@redhat.com>
        <9c798af6-aa2c-5f76-7a50-ef1983f9bdcd@redhat.com>
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On Tue, 27 Sep 2022 11:28:13 -0400
Waiman Long <longman@redhat.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@goodmis.org>
> > Signed-off-by: Waiman Long <longman@redhat.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