Prev: Fwd: [RFC][PATCH v1 11/15] perf: export tracepoint events via sysfs: power
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From: Dongdong Deng on 22 Jul 2010 22:20
The hw_breakpoint subsystem consumes all the hardware
breakpoint exceptions since it hooks the notify_die
handlers first, this means that kgdb doesn't get the
opportunity to handle hw breakpoint exceptions generated
by kgdb itself.

This patch adds an extend flag to perf_event_attr for
hw_breakpoint_handler() to decide to pass or stop the
DIE_DEBUG notification.

As KGDB set that flag, hw_breakpoint_handler() will pass
the DIE_DEBUG notification, thus kgdb have the chance
to take DIE_DEBUG notification.

Signed-off-by: Dongdong Deng <dongdong.deng(a)windriver.com>
Reviewed-by: Bruce Ashfield <bruce.ashfield(a)windriver.com>
---
arch/x86/kernel/hw_breakpoint.c | 14 ++++++++++++++
arch/x86/kernel/kgdb.c | 2 ++
include/linux/perf_event.h | 9 +++++++++
3 files changed, 25 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index a8f1b80..b38f786 100644
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -406,6 +406,8 @@ EXPORT_SYMBOL_GPL(hw_breakpoint_restore);
* ii) When there are more bits than trap<n> set in DR6 register (such
* as BD, BS or BT) indicating that more than one debug condition is
* met and requires some more action in do_debug().
+ * iii) The source of hw breakpoint event want to handle the event
+ * by itself, currently just KGDB have this notion.
*
* NOTIFY_STOP returned for all other cases
*
@@ -464,6 +466,18 @@ static int __kprobes hw_breakpoint_handler(struct die_args *args)
break;
}

+ if (bp->attr.flag == SKIP_HWBP_EVENT_PERF_FLAG) {
+ /*
+ * when attr.flag is set to SKIP_HWBP_EVENT_PERF_FLAG
+ * it indicates currently hw breakpoint event
+ * source want to handle this event by itself.
+ * thus return NOTIFY_DONE here.
+ */
+ rc = NOTIFY_DONE;
+ rcu_read_unlock();
+ break;
+ }
+
perf_bp_event(bp, args->regs);

rcu_read_unlock();
diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index 4f4af75..bc3321f 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -641,6 +641,8 @@ void kgdb_arch_late(void)
attr.bp_len = HW_BREAKPOINT_LEN_1;
attr.bp_type = HW_BREAKPOINT_W;
attr.disabled = 1;
+ /* set kgdb's special requires flag to perf_event */
+ attr.flag = SKIP_HWBP_EVENT_PERF_FLAG;
for (i = 0; i < 4; i++) {
if (breakinfo[i].pev)
continue;
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 5d0266d..fcefb09 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -160,6 +160,11 @@ enum perf_event_read_format {

#define PERF_ATTR_SIZE_VER0 64 /* sizeof first published struct */

+enum perf_event_attr_flag {
+ NOSET_PERF_FLAG = 0,
+ SKIP_HWBP_EVENT_PERF_FLAG = 1,
+};
+
/*
* Hardware event_id to monitor via a performance monitoring event:
*/
@@ -225,6 +230,10 @@ struct perf_event_attr {
__u32 bp_type;
__u64 bp_addr;
__u64 bp_len;
+ /*
+ * Ext flag, currently just kgdb used it.
+ */
+ enum perf_event_attr_flag flag;
};

/*
--
1.6.0.4

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