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

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Date:   Thu, 22 Sep 2022 16:31:46 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tracing: Disable interrupt or preemption before
 acquiring arch_spinlock_t

On Thu, Sep 22, 2022 at 09:31:58AM -0400, 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.
> 
> Suggested-by: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Waiman Long <longman@...hat.com>

This seems to be missing a Fixes: tag :-)