linux-kernel - Re: [PATCH v1 2/8] tracing/ftrace: guard syscall probe with preempt

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Message-ID: <20241003182304.2b04b74a@gandalf.local.home>
Date: Thu, 3 Oct 2024 18:23:04 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, linux-kernel@...r.kernel.org,
 Peter Zijlstra <peterz@...radead.org>, Alexei Starovoitov <ast@...nel.org>,
 Yonghong Song <yhs@...com>, "Paul E . McKenney" <paulmck@...nel.org>, Ingo
 Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Mark
 Rutland <mark.rutland@....com>, Alexander Shishkin
 <alexander.shishkin@...ux.intel.com>, Namhyung Kim <namhyung@...nel.org>,
 Andrii Nakryiko <andrii.nakryiko@...il.com>, bpf@...r.kernel.org, Joel
 Fernandes <joel@...lfernandes.org>, linux-trace-kernel@...r.kernel.org,
 Michael Jeanson <mjeanson@...icios.com>
Subject: Re: [PATCH v1 2/8] tracing/ftrace: guard syscall probe with
 preempt_notrace

On Thu,  3 Oct 2024 11:16:32 -0400
Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

> In preparation for allowing system call enter/exit instrumentation to
> handle page faults, make sure that ftrace can handle this change by
> explicitly disabling preemption within the ftrace system call tracepoint
> probes to respect the current expectations within ftrace ring buffer
> code.

The ftrace ring buffer doesn't expect preemption being disabled before use.
It will explicitly disable preemption.

I don't think this patch is needed.

-- Steve

> 
> This change does not yet allow ftrace to take page faults per se within
> its probe, but allows its existing probes to adapt to the upcoming
> change.
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> Cc: Michael Jeanson <mjeanson@...icios.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Yonghong Song <yhs@...com>
> Cc: Paul E. McKenney <paulmck@...nel.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
> Cc: bpf@...r.kernel.org
> Cc: Joel Fernandes <joel@...lfernandes.org>