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Message-ID: <60d293cb-3863-41c8-868d-59c7468e270e@efficios.com>
Date: Tue, 3 Sep 2024 09:42:22 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
Greg KH <gregkh@...uxfoundation.org>, Sean Christopherson
<seanjc@...gle.com>, Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
Yonghong Song <yhs@...com>, "Paul E . McKenney" <paulmck@...nel.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Namhyung Kim <namhyung@...nel.org>, bpf@...r.kernel.org,
Joel Fernandes <joel@...lfernandes.org>, linux-trace-kernel@...r.kernel.org,
Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v1 2/2] cleanup.h: Introduce DEFINE_INACTIVE_GUARD and
activate_guard
On 2024-09-02 14:46, Linus Torvalds wrote:
[...]
> IOW, that code should just have been something like this:
>
> #define __BPF_DECLARE_TRACE(call, proto, args, tp_flags) \
> static notrace void \
> __bpf_trace_##call(void *__data, proto) \
> { \
> \
> if ((tp_flags) & TRACEPOINT_MAY_FAULT) { \
> might_fault(); \
> guard(preempt_notrace)(); \
> CONCATENATE(bpf_trace_run, ... \
> return; \
> } \
> CONCATENATE(bpf_trace_run, ... \
> }
>
> instead.
If we look at perf_trace_##call(), with the conditional guard, it looks
like the following. It is not clear to me that code duplication would
be acceptable here.
I agree with you that the conditional guard is perhaps not something we
want at this stage, but in this specific case perhaps we should go back
to goto and labels ?
One alternative is to add yet another level of macros to handle the
code duplication.
#define _DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print, tp_flags) \
static notrace void \
perf_trace_##call(void *__data, proto) \
{ \
struct trace_event_call *event_call = __data; \
struct trace_event_data_offsets_##call __maybe_unused __data_offsets;\
struct trace_event_raw_##call *entry; \
struct pt_regs *__regs; \
u64 __count = 1; \
struct task_struct *__task = NULL; \
struct hlist_head *head; \
int __entry_size; \
int __data_size; \
int rctx; \
\
DEFINE_INACTIVE_GUARD(preempt_notrace, trace_event_guard); \
\
if ((tp_flags) & TRACEPOINT_MAY_FAULT) { \
might_fault(); \
activate_guard(preempt_notrace, trace_event_guard)(); \
} \
\
__data_size = trace_event_get_offsets_##call(&__data_offsets, args); \
\
head = this_cpu_ptr(event_call->perf_events); \
if (!bpf_prog_array_valid(event_call) && \
__builtin_constant_p(!__task) && !__task && \
hlist_empty(head)) \
return; \
\
__entry_size = ALIGN(__data_size + sizeof(*entry) + sizeof(u32),\
sizeof(u64)); \
__entry_size -= sizeof(u32); \
\
entry = perf_trace_buf_alloc(__entry_size, &__regs, &rctx); \
if (!entry) \
return; \
\
perf_fetch_caller_regs(__regs); \
\
tstruct \
\
{ assign; } \
\
perf_trace_run_bpf_submit(entry, __entry_size, rctx, \
event_call, __count, __regs, \
head, __task); \
}
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
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