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Commit 91e86e56 authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt
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tracing: Fix recursive user stack trace 



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: default avatarJiri Olsa <jolsa@redhat.com>
LKML-Reference: <1289390172-9730-3-git-send-email-jolsa@redhat.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent b5908548

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