Re: [PATCH 02b/10] perf, trace: Fix probe unregister race

Frederic Weisbecker
2010-05-21T10:44:11Z

On Fri, May 21, 2010 at 12:41:16PM +0200, Peter Zijlstra wrote:
> tracepoint_probe_unregister() does not synchronize against the probe callbacks,
> so do that explicitly. This properly serializes the callbacks and the free of
> the data used therein.
>
> Also, use this_cpu_ptr() where possible.
>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

Acked-by: Frederic Weisbecker <fweisbec@gmail.com>

(and you previous patches too)

> ---
> include/trace/ftrace.h | 2 +-
> kernel/trace/trace_event_perf.c | 10 ++++++++--
> kernel/trace/trace_kprobe.c | 4 ++--
> kernel/trace/trace_syscalls.c | 4 ++--
> 4 files changed, 13 insertions(+), 7 deletions(-)
>
> Index: linux-2.6/include/trace/ftrace.h
> ===================================================================
> --- linux-2.6.orig/include/trace/ftrace.h
> +++ linux-2.6/include/trace/ftrace.h
> @@ -791,7 +791,7 @@ perf_trace_templ_##call(struct ftrace_ev
> \
> { assign; } \
> \
> - head = per_cpu_ptr(event_call->perf_events, smp_processor_id());\
> + head = this_cpu_ptr(event_call->perf_events); \
> perf_trace_buf_submit(entry, __entry_size, rctx, __addr, \
> __count, __regs, head); \
> }
> Index: linux-2.6/kernel/trace/trace_event_perf.c
> ===================================================================
> --- linux-2.6.orig/kernel/trace/trace_event_perf.c
> +++ linux-2.6/kernel/trace/trace_event_perf.c
> @@ -109,7 +109,7 @@ int perf_trace_enable(struct perf_event
> if (WARN_ON_ONCE(!list))
> return -EINVAL;
>
> - list = per_cpu_ptr(list, smp_processor_id());
> + list = this_cpu_ptr(list);
> hlist_add_head_rcu(&p_event->hlist_entry, list);
>
> return 0;
> @@ -130,6 +130,12 @@ void perf_trace_destroy(struct perf_even
>
> tp_event->perf_event_disable(tp_event);
>
> + /*
> + * Ensure our callback won't be called anymore. See
> + * tracepoint_probe_unregister() and __DO_TRACE().
> + */
> + synchronize_sched();
> +
> free_percpu(tp_event->perf_events);
> tp_event->perf_events = NULL;
>
> @@ -156,7 +162,7 @@ __kprobes void *perf_trace_buf_prepare(i
> if (*rctxp < 0)
> return NULL;
>
> - raw_data = per_cpu_ptr(perf_trace_buf[*rctxp], smp_processor_id());
> + raw_data = this_cpu_ptr(perf_trace_buf[*rctxp]);
>
> /* zero the dead bytes from align to not leak stack to user */
> memset(&raw_data[size - sizeof(u64)], 0, sizeof(u64));
> Index: linux-2.6/kernel/trace/trace_kprobe.c
> ===================================================================
> --- linux-2.6.orig/kernel/trace/trace_kprobe.c
> +++ linux-2.6/kernel/trace/trace_kprobe.c
> @@ -1362,7 +1362,7 @@ static __kprobes void kprobe_perf_func(s
> for (i = 0; i < tp->nr_args; i++)
> call_fetch(&tp->args[i].fetch, regs, data + tp->args[i].offset);
>
> - head = per_cpu_ptr(call->perf_events, smp_processor_id());
> + head = this_cpu_ptr(call->perf_events);
> perf_trace_buf_submit(entry, size, rctx, entry->ip, 1, regs, head);
> }
>
> @@ -1395,7 +1395,7 @@ static __kprobes void kretprobe_perf_fun
> for (i = 0; i < tp->nr_args; i++)
> call_fetch(&tp->args[i].fetch, regs, data + tp->args[i].offset);
>
> - head = per_cpu_ptr(call->perf_events, smp_processor_id());
> + head = this_cpu_ptr(call->perf_events);
> perf_trace_buf_submit(entry, size, rctx, entry->ret_ip, 1, regs, head);
> }
>
> Index: linux-2.6/kernel/trace/trace_syscalls.c
> ===================================================================
> --- linux-2.6.orig/kernel/trace/trace_syscalls.c
> +++ linux-2.6/kernel/trace/trace_syscalls.c
> @@ -469,7 +469,7 @@ static void perf_syscall_enter(struct pt
> syscall_get_arguments(current, regs, 0, sys_data->nb_args,
> (unsigned long *)&rec->args);
>
> - head = per_cpu_ptr(sys_data->enter_event->perf_events, smp_processor_id());
> + head = this_cpu_ptr(sys_data->enter_event->perf_events);
> perf_trace_buf_submit(rec, size, rctx, 0, 1, regs, head);
> }
>
> @@ -545,7 +545,7 @@ static void perf_syscall_exit(struct pt_
> rec->nr = syscall_nr;
> rec->ret = syscall_get_return_value(current, regs);
>
> - head = per_cpu_ptr(sys_data->exit_event->perf_events, smp_processor_id());
> + head = this_cpu_ptr(sys_data->exit_event->perf_events);
> perf_trace_buf_submit(rec, size, rctx, 0, 1, regs, head);
> }
>
>
>