[tip: core/debugobjects] debugobjects: Free per CPU pool after CPU unplug

[tip-bot2 for Zqiang]

The following commit has been merged into the core/debugobjects branch of tip:

Commit-ID:     88451f2cd3cec2abc30debdf129422d2699d1eba
Gitweb:        https://git.kernel.org/tip/88451f2cd3cec2abc30debdf129422d2699d1eba
Author:        Zqiang <qiang.zhang@xxxxxxxxxxxxx>
AuthorDate:    Tue, 08 Sep 2020 14:27:09 +08:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Thu, 01 Oct 2020 16:13:54 +02:00

debugobjects: Free per CPU pool after CPU unplug

If a CPU is offlined the debug objects per CPU pool is not cleaned up. If
the CPU is never onlined again then the objects in the pool are wasted.

Add a CPU hotplug callback which is invoked after the CPU is dead to free
the pool.

[ tglx: Massaged changelog and added comment about remote access safety ]

Signed-off-by: Zqiang <qiang.zhang@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20200908062709.11441-1-qiang.zhang@xxxxxxxxxxxxx

---
 include/linux/cpuhotplug.h |  1 +
 lib/debugobjects.c         | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index bf9181c..6f524bb 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -36,6 +36,7 @@ enum cpuhp_state {
 	CPUHP_X86_MCE_DEAD,
 	CPUHP_VIRT_NET_DEAD,
 	CPUHP_SLUB_DEAD,
+	CPUHP_DEBUG_OBJ_DEAD,
 	CPUHP_MM_WRITEBACK_DEAD,
 	CPUHP_MM_VMSTAT_DEAD,
 	CPUHP_SOFTIRQ_DEAD,
diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index e2a3171..9e14ae0 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -19,6 +19,7 @@
 #include <linux/slab.h>
 #include <linux/hash.h>
 #include <linux/kmemleak.h>
+#include <linux/cpu.h>
 
 #define ODEBUG_HASH_BITS	14
 #define ODEBUG_HASH_SIZE	(1 << ODEBUG_HASH_BITS)
@@ -433,6 +434,25 @@ static void free_object(struct debug_obj *obj)
 	}
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+static int object_cpu_offline(unsigned int cpu)
+{
+	struct debug_percpu_free *percpu_pool;
+	struct hlist_node *tmp;
+	struct debug_obj *obj;
+
+	/* Remote access is safe as the CPU is dead already */
+	percpu_pool = per_cpu_ptr(&percpu_obj_pool, cpu);
+	hlist_for_each_entry_safe(obj, tmp, &percpu_pool->free_objs, node) {
+		hlist_del(&obj->node);
+		kmem_cache_free(obj_cache, obj);
+	}
+	percpu_pool->obj_free = 0;
+
+	return 0;
+}
+#endif
+
 /*
  * We run out of memory. That means we probably have tons of objects
  * allocated.
@@ -1367,6 +1387,11 @@ void __init debug_objects_mem_init(void)
 	} else
 		debug_objects_selftest();
 
+#ifdef CONFIG_HOTPLUG_CPU
+	cpuhp_setup_state_nocalls(CPUHP_DEBUG_OBJ_DEAD, "object:offline", NULL,
+					object_cpu_offline);
+#endif
+
 	/*
 	 * Increase the thresholds for allocating and freeing objects
 	 * according to the number of possible CPUs available in the system.