tracing: Fix recursive user stack trace (91e86e56) · Commits · 戴 / test

The user stack trace can fault when examining the trace. Which would call the do_page_fault handler, which would trace again, which would do the user stack trace, which would fault and call do_page_fault again ... Thus this is causing a recursive bug. We need to have a recursion detector here. [ Resubmitted by Jiri Olsa ] [ Eric Dumazet recommended using __this_cpu_* instead of __get_cpu_* ] Cc: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by:

Jiri Olsa <jolsa@redhat.com> LKML-Reference: <1289390172-9730-3-git-send-email-jolsa@redhat.com> Signed-off-by:

Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.c

+19 −0

Original line number	Diff line number	Diff line
		@@ -1284,6 +1284,8 @@ void trace_dump_stack(void)
		__ftrace_trace_stack(global_trace.buffer, flags, 3, preempt_count());
		}

		static DEFINE_PER_CPU(int, user_stack_count);

		void
		ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc)
		{
		@@ -1302,6 +1304,18 @@ ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc)
		if (unlikely(in_nmi()))
		return;

		/*
		* prevent recursion, since the user stack tracing may
		* trigger other kernel events.
		*/
		preempt_disable();
		if (__this_cpu_read(user_stack_count))
		goto out;

		__this_cpu_inc(user_stack_count);



		event = trace_buffer_lock_reserve(buffer, TRACE_USER_STACK,
		sizeof(*entry), flags, pc);
		if (!event)
		@@ -1319,6 +1333,11 @@ ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc)
		save_stack_trace_user(&trace);
		if (!filter_check_discard(call, entry, buffer, event))
		ring_buffer_unlock_commit(buffer, event);

		__this_cpu_dec(user_stack_count);

		out:
		preempt_enable();
		}

		#ifdef UNUSED

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