hw_breakpoint: Simplify list/idx mess in toggle_bp_slot() paths

The enable/disable logic in toggle_bp_slot() is not symmetrical and imho very confusing. "old_count" in toggle_bp_task_slot() is actually new_count because this bp was already removed from the list. Change toggle_bp_slot() to always call list_add/list_del after toggle_bp_task_slot(). This way old_idx is task_bp_pinned() and this entry should be decremented, new_idx is +/-weight and we need to increment this element. The code/logic looks obvious. Reported-by: Vince Weaver <vincent.weaver@maine.edu> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Frederic Weisbecker <fweisbec@gmail.com> Link: http://lkml.kernel.org/r/20130620155011.GA6330@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>

hw_breakpoint: Simplify list/idx mess in toggle_bp_slot() paths
The enable/disable logic in toggle_bp_slot() is not symmetrical and imho very confusing. "old_count" in toggle_bp_task_slot() is actually new_count because this bp was already removed from the list. Change toggle_bp_slot() to always call list_add/list_del after toggle_bp_task_slot(). This way old_idx is task_bp_pinned() and this entry should be decremented, new_idx is +/-weight and we need to increment this element. The code/logic looks obvious. Reported-by: Vince Weaver <vincent.weaver@maine.edu> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Frederic Weisbecker <fweisbec@gmail.com> Link: http://lkml.kernel.org/r/20130620155011.GA6330@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Oleg Nesterov · Ingo Molnar
1 parent f070a4dba9
Showing 1 changed file with 16 additions and 24 deletions Side-by-side Diff
kernel/events/hw_breakpoint.c
@@ -185,26 +185,20 @@
 static void toggle_bp_task_slot(struct perf_event *bp, int cpu, bool enable,
 				enum bp_type_idx type, int weight)
 {
-	unsigned int *tsk_pinned;
-	int old_count = 0;
-	int old_idx = 0;
-	int idx = 0;
+	/* tsk_pinned[n-1] is the number of tasks having n>0 breakpoints */
+	unsigned int *tsk_pinned = per_cpu(nr_task_bp_pinned[type], cpu);
+	int old_idx, new_idx;
  
-	old_count = task_bp_pinned(cpu, bp, type);
-	old_idx = old_count - 1;
-	idx = old_idx + weight;
+	old_idx = task_bp_pinned(cpu, bp, type) - 1;
+	if (enable)
+		new_idx = old_idx + weight;
+	else
+		new_idx = old_idx - weight;
  
-	/* tsk_pinned[n] is the number of tasks having n breakpoints */
-	tsk_pinned = per_cpu(nr_task_bp_pinned[type], cpu);
-	if (enable) {
-		tsk_pinned[idx]++;
-		if (old_count > 0)
-			tsk_pinned[old_idx]--;
-	} else {
-		tsk_pinned[idx]--;
-		if (old_count > 0)
-			tsk_pinned[old_idx]++;
-	}
+	if (old_idx >= 0)
+		tsk_pinned[old_idx]--;
+	if (new_idx >= 0)
+		tsk_pinned[new_idx]++;
 }
  
 /*
@@ -228,10 +222,6 @@
 	}
  
 	/* Pinned counter task profiling */
-
-	if (!enable)
-		list_del(&bp->hw.bp_list);
-
 	if (cpu >= 0) {
 		toggle_bp_task_slot(bp, cpu, enable, type, weight);
 	} else {
@@ -241,6 +231,8 @@
  
 	if (enable)
 		list_add_tail(&bp->hw.bp_list, &bp_task_head);
+	else
+		list_del(&bp->hw.bp_list);
 }
  
 /*
...	...	@@ -185,26 +185,20 @@
185	185	static void toggle_bp_task_slot(struct perf_event *bp, int cpu, bool enable,
186	186	enum bp_type_idx type, int weight)
187	187	{
188		- unsigned int *tsk_pinned;
189		- int old_count = 0;
190		- int old_idx = 0;
191		- int idx = 0;
	188	+ /* tsk_pinned[n-1] is the number of tasks having n>0 breakpoints */
	189	+ unsigned int *tsk_pinned = per_cpu(nr_task_bp_pinned[type], cpu);
	190	+ int old_idx, new_idx;
192	191
193		- old_count = task_bp_pinned(cpu, bp, type);
194		- old_idx = old_count - 1;
195		- idx = old_idx + weight;
	192	+ old_idx = task_bp_pinned(cpu, bp, type) - 1;
	193	+ if (enable)
	194	+ new_idx = old_idx + weight;
	195	+ else
	196	+ new_idx = old_idx - weight;
196	197
197		- /* tsk_pinned[n] is the number of tasks having n breakpoints */
198		- tsk_pinned = per_cpu(nr_task_bp_pinned[type], cpu);
199		- if (enable) {
200		- tsk_pinned[idx]++;
201		- if (old_count > 0)
202		- tsk_pinned[old_idx]--;
203		- } else {
204		- tsk_pinned[idx]--;
205		- if (old_count > 0)
206		- tsk_pinned[old_idx]++;
207		- }
	198	+ if (old_idx >= 0)
	199	+ tsk_pinned[old_idx]--;
	200	+ if (new_idx >= 0)
	201	+ tsk_pinned[new_idx]++;
208	202	}
209	203
210	204	/*
...	...	@@ -228,10 +222,6 @@
228	222	}
229	223
230	224	/* Pinned counter task profiling */
231		-
232		- if (!enable)
233		- list_del(&bp->hw.bp_list);
234		-
235	225	if (cpu >= 0) {
236	226	toggle_bp_task_slot(bp, cpu, enable, type, weight);
237	227	} else {
...	...	@@ -241,6 +231,8 @@
241	231
242	232	if (enable)
243	233	list_add_tail(&bp->hw.bp_list, &bp_task_head);
	234	+ else
	235	+ list_del(&bp->hw.bp_list);
244	236	}
245	237
246	238	/*