perf/hwbp: Simplify the perf-hwbp code, fix documentation

Annoyingly, modify_user_hw_breakpoint() unnecessarily complicates the
modification of a breakpoint - simplify it and remove the pointless
local variables.

Also update the stale Docbook while at it.

Signed-off-by: Linus Torvalds <[email protected]>
Acked-by: Thomas Gleixner <[email protected]>
Cc: <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Vince Weaver <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>

Author: torvalds

kernel/events/hw_breakpoint.c

@@ -427,16 +427,9 @@ EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
  * modify_user_hw_breakpoint - modify a user-space hardware breakpoint
  * @bp: the breakpoint structure to modify
  * @attr: new breakpoint attributes
- * @triggered: callback to trigger when we hit the breakpoint
- * @tsk: pointer to 'task_struct' of the process to which the address belongs
  */
 int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
 {
-	u64 old_addr = bp->attr.bp_addr;
-	u64 old_len = bp->attr.bp_len;
-	int old_type = bp->attr.bp_type;
-	int err = 0;
-
 	/*
 	 * modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
 	 * will not be possible to raise IPIs that invoke __perf_event_disable.
@@ -451,27 +444,18 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
 	bp->attr.bp_addr = attr->bp_addr;
 	bp->attr.bp_type = attr->bp_type;
 	bp->attr.bp_len = attr->bp_len;
+	bp->attr.disabled = 1;
 
-	if (attr->disabled)
-		goto end;
-
-	err = validate_hw_breakpoint(bp);
-	if (!err)
-		perf_event_enable(bp);
+	if (!attr->disabled) {
+		int err = validate_hw_breakpoint(bp);
 
-	if (err) {
-		bp->attr.bp_addr = old_addr;
-		bp->attr.bp_type = old_type;
-		bp->attr.bp_len = old_len;
-		if (!bp->attr.disabled)
-			perf_event_enable(bp);
+		if (err)
+			return err;
 
-		return err;
+		perf_event_enable(bp);
+		bp->attr.disabled = 0;
 	}
 
-end:
-	bp->attr.disabled = attr->disabled;
-
 	return 0;
 }
 EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);