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

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Date:   Thu, 22 Sep 2022 10:48:59 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 9/22/22 10:31, Peter Zijlstra wrote:
> 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 :-)

Sorry for the omission. The patch should have the following fixes tags.

Fixes: a35873a0993b ("tracing: Add conditional snapshot")
Fixes: 939c7a4f04fc ("tracing: Introduce saved_cmdlines_size file")

Cheers,
Longman