x86, mm, perf: Allow recursive faults from interrupts

x86, mm, perf: Allow recursive faults from interrupts

Waiman managed to trigger a PMI while in a emulate_vsyscall() fault,
the PMI in turn managed to trigger a fault while obtaining a stack
trace. This triggered the sig_on_uaccess_error recursive fault logic
and killed the process dead.

Fix this by explicitly excluding interrupts from the recursive fault
logic.

Reported-and-Tested-by: Waiman Long <[email protected]>
Fixes: e00b12e64be9 ("perf/x86: Further optimize copy_from_user_nmi()")
Cc: Aswin Chandramouleeswaran <[email protected]>
Cc: Scott J Norton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Andrew Morton <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>