[RFC Patch 3/5] PERF-HW_BKPT: Fix traceback seen when resumingafter suspend-to-ram

[K.Prasad]

Load the debug registers (when a CPU turns online) through a tasklet. This
helps to keep routines (using protected hw-breakpoint data) to be invoked
only from non-interrupt context, thus making the spin_lock_bh() locking
sufficient.

Signed-off-by: K.Prasad <prasad@xxxxxxxxxxxxxxxxxx>
---
 kernel/hw_breakpoint.c |   26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

Index: linux-2.6-tip.perf_hbkpt/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6-tip.perf_hbkpt.orig/kernel/hw_breakpoint.c
+++ linux-2.6-tip.perf_hbkpt/kernel/hw_breakpoint.c
@@ -23,6 +23,7 @@
  * This file contains the arch-independent routines.
  */
 
+#include <linux/interrupt.h>
 #include <linux/irqflags.h>
 #include <linux/kallsyms.h>
 #include <linux/notifier.h>
@@ -69,20 +70,19 @@ unsigned int hbp_user_refcount[HBP_NUM];
 static DEFINE_PER_CPU(int, hbp_consumed);
 
 /*
- * Load the debug registers during startup of a CPU.
+ * A tasklet to populate the debug register's values from the
+ * breakpoint structure
  */
-void load_debug_registers(void)
+static struct tasklet_struct hbp_tasklet;
+
+/* Tasklet function that populates the debug registers */
+void hbp_tasklet_function(unsigned long unused)
 {
-	unsigned long flags;
 	struct task_struct *tsk = current;
 
 	spin_lock_bh(&hw_breakpoint_lock);
 
-	/* Prevent IPIs for new kernel breakpoint updates */
-	local_irq_save(flags);
 	arch_update_kernel_hw_breakpoint(NULL);
-	local_irq_restore(flags);
-
 	if (test_tsk_thread_flag(tsk, TIF_DEBUG))
 		arch_install_thread_hw_breakpoint(tsk);
 
@@ -90,6 +90,18 @@ void load_debug_registers(void)
 }
 
 /*
+ * Load the debug registers during startup of a CPU.
+ */
+void load_debug_registers(void)
+{
+	unsigned long flags;
+
+	if (!hbp_tasklet.func)
+		tasklet_init(&hbp_tasklet, &hbp_tasklet_function, 0UL);
+	tasklet_schedule(&hbp_tasklet);
+}
+
+/*
  * Erase all the hardware breakpoint info associated with a thread.
  *
  * If tsk != current then tsk must not be usable (for example, a


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