[Patch 1/1] Introduce register_user_hbp_by_pid() and unregister_user_hbp_by_pid()

["K.Prasad" <prasad@linux.vnet.ibm.com>]

Provide an interface to (un)register user-space breakpoints using a
process' pid.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 include/linux/hw_breakpoint.h |    8 +++
 kernel/hw_breakpoint.c        |   92 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 100 insertions(+)

Index: linux-2.6-tip.reg_by_pid/include/linux/hw_breakpoint.h
===================================================================
--- linux-2.6-tip.reg_by_pid.orig/include/linux/hw_breakpoint.h
+++ linux-2.6-tip.reg_by_pid/include/linux/hw_breakpoint.h
@@ -54,6 +54,10 @@ register_user_hw_breakpoint(struct perf_
 			    perf_overflow_handler_t triggered,
 			    struct task_struct *tsk);
 
+extern int register_user_hbp_by_pid(struct perf_event_attr *attr,
+			 perf_overflow_handler_t triggered,
+			 pid_t pid);
+extern void unregister_user_hbp_by_pid(pid_t pid);
 /* FIXME: only change from the attr, and don't unregister */
 extern int
 modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr);
@@ -91,6 +95,10 @@ static inline struct perf_event *
 register_user_hw_breakpoint(struct perf_event_attr *attr,
 			    perf_overflow_handler_t triggered,
 			    struct task_struct *tsk)	{ return NULL; }
+int register_user_hbp_by_pid(struct perf_event_attr *attr,
+			 perf_overflow_handler_t triggered,
+			 pid_t pid)	{ return 0; }
+void unregister_user_hbp_by_pid(pid_t pid) {}
 static inline int
 modify_user_hw_breakpoint(struct perf_event *bp,
 			  struct perf_event_attr *attr)	{ return -ENOSYS; }
Index: linux-2.6-tip.reg_by_pid/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6-tip.reg_by_pid.orig/kernel/hw_breakpoint.c
+++ linux-2.6-tip.reg_by_pid/kernel/hw_breakpoint.c
@@ -298,6 +298,98 @@ int register_perf_hw_breakpoint(struct p
 	return ret;
 }
 
+/*
+ * Unregister breakpoints thread-by-thread, for all threads ranging from
+ * @start to @end.
+ */
+static inline void __unregister_user_hbp_for_threads(struct task_struct *start,
+						struct task_struct *end)
+{
+	struct perf_event *bp, *temp_bp;
+
+	do {
+		mutex_lock(&start->perf_event_mutex);
+		list_for_each_entry_safe(bp, temp_bp, &start->perf_event_list,
+					 owner_entry) {
+			if (bp->attr.type != PERF_TYPE_BREAKPOINT)
+				continue;
+			unregister_hw_breakpoint(bp);
+			break;
+		}
+		mutex_unlock(&start->perf_event_mutex);
+	} while_each_thread(start, end);
+}
+
+/**
+ * register_user_hbp_by_pid - register a hardware breakpoint for user space using pid
+ * @attr: breakpoint attributes
+ * @triggered: callback to trigger when we hit the breakpoint
+ * @pid: pid of the thread group for which breakpoints must be registered
+ */
+int register_user_hbp_by_pid(struct perf_event_attr *attr,
+			 perf_overflow_handler_t triggered,
+			 pid_t pid)
+{
+	int ret;
+	struct task_struct *t1, *t2;
+
+	t1 = t2 = find_task_by_vpid(pid);
+	if (t1 == NULL)
+		return -ESRCH;
+
+	/*
+	 * Ensure that the breakpoint propogates to every new thread created in
+	 * this thread_group.
+	 */
+	attr->inherit = 1;
+	/*
+	 * Register a breakpoint individually for every thread of the
+	 * thread_group using register_user_hw_breakpoint() interface.
+	 * Warning: Involves redundant validation checks using
+	 * arch_validate_hwbkpt_settings().
+	 */
+	do {
+		ret = IS_ERR(register_user_hw_breakpoint(attr, triggered, t1));
+		if (ret)
+			goto fail;
+		t1 = next_thread(t1);
+	} while (t1 != t2);
+
+	return 0;
+fail:
+	/*
+	 * Check if the very first register_user_hw_breakpoint() request
+	 * failed. If then, do nothing but return the error value.
+	 */
+	if (t1 == t2)
+		return ret;
+	/*
+	 * Since there exists a thread where the breakpoint request was not
+	 * successful, we are unable to provide a process-wide breakpoint. Hence
+	 * cleanup the breakpoints from the previously registered threads.
+	 */
+	__unregister_user_hbp_for_threads(t2, t1);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(register_user_hbp_by_pid);
+
+/**
+ * unregister_hbp_by_pid - unregister a user-space hardware breakpoint previously registered using a pid
+ * @pid: pid of the process for which breakpoint must be unregistered
+ */
+void unregister_user_hbp_by_pid(pid_t pid)
+{
+	struct task_struct *t1, *t2;
+
+	t1 = t2 = find_task_by_vpid(pid);
+	if (t1 == NULL)
+		return;
+
+	__unregister_user_hbp_for_threads(t1, t2);
+}
+EXPORT_SYMBOL_GPL(unregister_user_hbp_by_pid);
+
 /**
  * register_user_hw_breakpoint - register a hardware breakpoint for user space
  * @attr: breakpoint attributes