Messages in this thread Patch in this message | | | From | Jiri Olsa <> | Subject | [PATCHv2 1/2] tracing - fix recursive user stack trace | Date | Thu, 11 Nov 2010 10:09:08 +0100 |
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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.
Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Jiri Olsa <jolsa@redhat.com> --- kernel/trace/trace.c | 17 +++++++++++++++++ 1 files changed, 17 insertions(+), 0 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 82d9b81..1905a72 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -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 +1304,16 @@ 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 (__get_cpu_var(user_stack_count)) + goto out; + + __get_cpu_var(user_stack_count)++; + event = trace_buffer_lock_reserve(buffer, TRACE_USER_STACK, sizeof(*entry), flags, pc); if (!event) @@ -1319,6 +1331,11 @@ 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); + + __get_cpu_var(user_stack_count)--; + + out: + preempt_enable(); } #ifdef UNUSED -- 1.7.1
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