[PATCH 7/9] perf/ftrace: Add recursion protection to the ftrace callback

Steven Rostedt
2020-10-28T22:18:36Z

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

If a ftrace callback does not supply its own recursion protection and
does not set the RECURSION_SAFE flag in its ftrace_ops, then ftrace will
make a helper trampoline to do so before calling the callback instead of
just calling the callback directly.

The default for ftrace_ops is going to assume recursion protection unless
otherwise specified.

Cc: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/trace/trace_event_perf.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 643e0b19920d..fd58d83861d8 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -439,10 +439,15 @@ perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip,
struct hlist_head head;
struct pt_regs regs;
int rctx;
+ int bit;

if ((unsigned long)ops->private != smp_processor_id())
return;

+ bit = ftrace_test_recursion_trylock();
+ if (bit < 0)
+ return;
+
event = container_of(ops, struct perf_event, ftrace_ops);

/*
@@ -463,13 +468,15 @@ perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip,

entry = perf_trace_buf_alloc(ENTRY_SIZE, NULL, &rctx);
if (!entry)
- return;
+ goto out;

entry->ip = ip;
entry->parent_ip = parent_ip;
perf_trace_buf_submit(entry, ENTRY_SIZE, rctx, TRACE_FN,
1, &regs, &head, NULL);

+out:
+ ftrace_test_recursion_unlock(bit);
#undef ENTRY_SIZE
}

--
2.28.0