From: Steven Rostedt <rostedt@goodmis.org>
To: patrick wang <patrick.wang.shcn@gmail.com>
Cc: paulmck@kernel.org, frederic@kernel.org,
quic_neeraju@quicinc.com, josh@joshtriplett.org,
mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
joel@joelfernandes.org, rcu@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] rcu: ftrace: avoid tracing a few functions executed in multi_cpu_stop()
Date: Thu, 21 Apr 2022 08:50:47 -0400 [thread overview]
Message-ID: <20220421085047.2cb8edf9@gandalf.local.home> (raw)
In-Reply-To: <CAGcnep86pd2trfTovU8_z1msOstx7gKCdndm=pHLDGTy+_K7=g@mail.gmail.com>
On Thu, 21 Apr 2022 19:36:06 +0800
patrick wang <patrick.wang.shcn@gmail.com> wrote:
> On Thu, Apr 21, 2022 at 12:26 AM Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > On Wed, 20 Apr 2022 11:44:54 -0400
> > Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> >
> > Interesting. On x86 when we used stop machine[*] it was not an issue to
> > modify the code that is being executed in stop machine. I'm curious to
> > exactly what the issue is if something does get traced in the stop machine
> > processing. Why does it crash?
>
> I looked up the commit history. When x86 turned to breakpoints, stop
> machine's state machine loop had no calls during waiting. So there
> was no function being called during modifying code. Which means
> there were no other cpus would load those instructions to be updated
> in this period. While the stop machine currently will call other functions
> and the call chain is fairly deep. So it may not quite be suitable for ftrace
> now because it can not make sure the instructions within its own call
> chain are updated atomically.
Are you saying that the RISC-V stop machine implementation has code being
called on the other CPUs while they wait?
-- Steve
next prev parent reply other threads:[~2022-04-21 12:50 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-18 4:37 [PATCH] rcu: ftrace: avoid tracing a few functions executed in multi_cpu_stop() Patrick Wang
2022-04-18 16:28 ` Paul E. McKenney
2022-04-18 18:34 ` Steven Rostedt
2022-04-19 4:06 ` patrick wang
2022-04-20 10:34 ` patrick wang
2022-04-20 15:44 ` Steven Rostedt
2022-04-20 16:26 ` Steven Rostedt
2022-04-21 11:36 ` patrick wang
2022-04-21 12:50 ` Steven Rostedt [this message]
2022-04-22 10:45 ` patrick wang
2022-04-22 15:52 ` Steven Rostedt
2022-04-23 9:43 ` patrick wang
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