[RFC PATCH] perf: fix panic by mark recursion inside perf_log_throttle

[王贇]

When running with ftrace function enabled, we observed panic
as below:

  traps: PANIC: double fault, error_code: 0x0
  [snip]
  RIP: 0010:perf_swevent_get_recursion_context+0x0/0x70
  [snip]
  Call Trace:
   <NMI>
   perf_trace_buf_alloc+0x26/0xd0
   perf_ftrace_function_call+0x18f/0x2e0
   kernelmode_fixup_or_oops+0x5/0x120
   __bad_area_nosemaphore+0x1b8/0x280
   do_user_addr_fault+0x410/0x920
   exc_page_fault+0x92/0x300
   asm_exc_page_fault+0x1e/0x30
  RIP: 0010:__get_user_nocheck_8+0x6/0x13
   perf_callchain_user+0x266/0x2f0
   get_perf_callchain+0x194/0x210
   perf_callchain+0xa3/0xc0
   perf_prepare_sample+0xa5/0xa60
   perf_event_output_forward+0x7b/0x1b0
   __perf_event_overflow+0x67/0x120
   perf_swevent_overflow+0xcb/0x110
   perf_swevent_event+0xb0/0xf0
   perf_tp_event+0x292/0x410
   perf_trace_run_bpf_submit+0x87/0xc0
   perf_trace_lock_acquire+0x12b/0x170
   lock_acquire+0x1bf/0x2e0
   perf_output_begin+0x70/0x4b0
   perf_log_throttle+0xe2/0x1a0
   perf_event_nmi_handler+0x30/0x50
   nmi_handle+0xba/0x2a0
   default_do_nmi+0x45/0xf0
   exc_nmi+0x155/0x170
   end_repeat_nmi+0x16/0x55

According to the trace we know the story is like this, the NMI
triggered perf IRQ throttling and call perf_log_throttle(),
which triggered the swevent overflow, and the overflow process
do perf_callchain_user() which triggered a user PF, and the PF
process triggered perf ftrace which finally lead into a suspected
stack overflow.

This patch marking the context as recursion during perf_log_throttle()
, so no more swevent during the process and no more panic.

Signed-off-by: Michael Wang <yun.wang@xxxxxxxxxxxxxxxxx>
---
 kernel/events/core.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 744e872..6063443 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8716,6 +8716,7 @@ static void perf_log_throttle(struct perf_event *event, int enable)
 	struct perf_output_handle handle;
 	struct perf_sample_data sample;
 	int ret;
+	int rctx;

 	struct {
 		struct perf_event_header	header;
@@ -8738,14 +8739,17 @@ static void perf_log_throttle(struct perf_event *event, int enable)

 	perf_event_header__init_id(&throttle_event.header, &sample, event);

+	rctx = perf_swevent_get_recursion_context();
 	ret = perf_output_begin(&handle, &sample, event,
 				throttle_event.header.size);
-	if (ret)
-		return;
+	if (!ret) {
+		perf_output_put(&handle, throttle_event);
+		perf_event__output_id_sample(event, &handle, &sample);
+		perf_output_end(&handle);
+	}

-	perf_output_put(&handle, throttle_event);
-	perf_event__output_id_sample(event, &handle, &sample);
-	perf_output_end(&handle);
+	if (rctx >= 0)
+		perf_swevent_put_recursion_context(rctx);
 }

 /*
-- 
1.8.3.1