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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: Jiri Olsa <jolsa@redhat.com>
LKML-Reference: <1289390172-9730-3-git-send-email-jolsa@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2010-11-10 12:56:12 +01:00 committed by Steven Rostedt
parent b590854853
commit 91e86e560d
1 changed files with 19 additions and 0 deletions
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19
kernel/trace/trace.c
View File

@ -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