perf, hw_breakpoint: Fix crash in hw_breakpoint creation

hw_breakpoint creation needs to account stuff per-task to ensure there
is always sufficient hardware resources to back these things due to
ptrace.

With the perf per pmu context changes the event initialization no
longer has access to the event context, for the simple reason that we
need to first find the pmu (result of initialization) before we can
find the context.

This makes hw_breakpoints unhappy, because it can no longer do per
task accounting, cure this by frobbing a task pointer in the event::hw
bits for now...

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20101014203625.391543667@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 2ebfc9ae4755..97965fac55fe 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -536,6 +536,12 @@ struct hw_perf_event {
                 struct { /* breakpoint */
                         struct arch_hw_breakpoint       info;
                         struct list_head                bp_list;
+                        /*
+                         * Crufty hack to avoid the chicken and egg
+                         * problem hw_breakpoint has with context
+                         * creation and event initalization.
+                         */
+                        struct task_struct              *bp_target;
                 };
 #endif
         };
@@ -693,6 +699,7 @@ struct swevent_hlist {
 
 #define PERF_ATTACH_CONTEXT     0x01
 #define PERF_ATTACH_GROUP       0x02
+#define PERF_ATTACH_TASK        0x04
 
 /**
  * struct perf_event - performance event kernel representation: