linux-kernel - Re: [PATCH v5 1/1] blktrace: switch trace spinlock to a raw spinlock

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Message-ID: <b07b97b4-dff2-5915-ce56-a039a14a74dd@kernel.dk>
Date:   Mon, 20 Dec 2021 13:24:52 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Wander Costa <wcosta@...hat.com>
Cc:     Wander Lairson Costa <wander@...hat.com>,
        open list <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        "open list:BLOCK LAYER" <linux-block@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH v5 1/1] blktrace: switch trace spinlock to a raw spinlock

On 12/20/21 12:49 PM, Wander Costa wrote:
> On Mon, Dec 20, 2021 at 4:38 PM Jens Axboe <axboe@...nel.dk> wrote:
>>
>> On 12/20/21 12:28 PM, Wander Lairson Costa wrote:
>>> The running_trace_lock protects running_trace_list and is acquired
>>> within the tracepoint which implies disabled preemption. The spinlock_t
>>> typed lock can not be acquired with disabled preemption on PREEMPT_RT
>>> because it becomes a sleeping lock.
>>> The runtime of the tracepoint depends on the number of entries in
>>> running_trace_list and has no limit. The blk-tracer is considered debug
>>> code and higher latencies here are okay.
>>
>> You didn't put a changelog in here. Was this one actually compiled? Was
>> it runtime tested?
> 
> It feels like the changelog reached the inboxes after patch (at least
> mine was so). Would you like that I send a v6 in the hope things
> arrive in order?

Not sure how you are sending them, but they don't appear to thread
properly. But the changelog in the cover letter isn't really a
changelog, it doesn't say what changed.

-- 
Jens Axboe