linux-kernel - Re: [PATCH v2 0/7] tracing: Allow system call tracepoints to handle page faults

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Message-ID: <1aff8385-083e-4d8d-9c81-ce8d54b688ed@efficios.com>
Date: Fri, 4 Oct 2024 10:49:36 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Steven Rostedt <rostedt@...dmis.org>,
 Masami Hiramatsu <mhiramat@...nel.org>
Cc: 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
Subject: Re: [PATCH v2 0/7] tracing: Allow system call tracepoints to handle
 page faults

On 2024-10-04 03:11, Mathieu Desnoyers wrote:
> Wire up the system call tracepoints with Tasks Trace RCU to allow
> the ftrace, perf, and eBPF tracers to handle page faults.
> 
> This series does the initial wire-up allowing tracers to handle page
> faults, but leaves out the actual handling of said page faults as future
> work.
> 
> This series was compile and runtime tested with ftrace and perf syscall
> tracing and raw syscall tracing, adding a WARN_ON_ONCE() in the
> generated code to validate that the intended probes are used for raw
> syscall tracing. The might_fault() added within those probes validate
> that they are called from a context where handling a page fault is OK.
> 
> This series replaces the "Faultable Tracepoints v6" series found at [1].
> 
> This has been rebased on v6.12-rc1 on top of two patches from Steven:
> 
> tracing: Remove definition of trace_*_rcuidle()
> tracepoint: Remove SRCU protection

I'll send an updated series which includes
"tracing: Declare system call tracepoints with TRACE_EVENT_SYSCALL"
(missing here), and which rework that patch to remove the mapping from
trace_sys_enter/exit to trace_syscall_sys_enter/exit which requires
modifying architecture code. A lot of churn for little value add.

Thanks,

Mathieu

> 
> Thanks,
> 
> Mathieu
> 
> Link: https://lore.kernel.org/lkml/20240828144153.829582-1-mathieu.desnoyers@efficios.com/ # [1]
> 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>
> Cc: linux-trace-kernel@...r.kernel.org
> 
> Mathieu Desnoyers (7):
>    tracing/ftrace: guard syscall probe with preempt_notrace
>    tracing/perf: guard syscall probe with preempt_notrace
>    tracing/bpf: guard syscall probe with preempt_notrace
>    tracing: Allow system call tracepoints to handle page faults
>    tracing/ftrace: Add might_fault check to syscall probes
>    tracing/perf: Add might_fault check to syscall probes
>    tracing/bpf: Add might_fault check to syscall probes
> 
>   include/linux/tracepoint.h    | 18 ++++++++++-----
>   include/trace/bpf_probe.h     | 12 +++++++++-
>   include/trace/perf.h          | 42 +++++++++++++++++++++++++++++++----
>   include/trace/trace_events.h  | 39 ++++++++++++++++++++++++++------
>   init/Kconfig                  |  1 +
>   kernel/trace/trace_syscalls.c | 28 +++++++++++++++++++++++
>   6 files changed, 123 insertions(+), 17 deletions(-)
> 

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com