linux-kernel - Re: [PATCH v4 5/5] blktrace: Make init_blk_tracer() asynchronous when trace_async

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Message-ID: <20260129152958.05c1ca46@gandalf.local.home>
Date: Thu, 29 Jan 2026 15:29:58 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Jens Axboe <axboe@...nel.dk>
Cc: Yaxiong Tian <tianyaxiong@...inos.cn>, mhiramat@...nel.org,
 mathieu.desnoyers@...icios.com, corbet@....net, skhan@...uxfoundation.org,
 linux-trace-kernel@...r.kernel.org, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v4 5/5] blktrace: Make init_blk_tracer() asynchronous
 when trace_async_init set

On Wed, 28 Jan 2026 19:25:46 -0700
Jens Axboe <axboe@...nel.dk> wrote:

> On Jan 28, 2026, at 5:40 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> > 
> > 
> > Jens,
> > 
> > Can you give me an acked-by on this patch and I can take the series through
> > my tree.  
> 
> On phone, hope this works:
> 
> Acked-by: Jens Axboe <axboe@...nel.dk>

Thanks!

> 
> > Or perhaps this doesn't even need to test the trace_async_init flag and can
> > always do the work queue? Does blk_trace ever do tracing at boot up? That
> > is, before user space starts?  
> 
> Not via the traditonal way of running blktrace.

Masami and Yaxiong,

I've been thinking about this more and I'm not sure we need the
trace_async_init kernel parameter at all. As blktrace should only be
enabled by user space, it can always use the work queue.

For kprobes, if someone is adding a kprobe on the kernel command line, then
they are already specifying that tracing is more important.

Patch 3 already keeps kprobes from being an issue with contention of the
tracing locks, so I don't think it ever needs to use the work queue.

Wouldn't it just be better to remove the trace_async_init and make blktrace
always use the work queue and kprobes never do it (but exit out early if
there were no kprobes registered)?

That is, remove patch 2 and 4 and make this patch always use the work queue.

-- Steve