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-rw-r--r--include/linux/rcupdate.h18
1 files changed, 18 insertions, 0 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 20fb776a1d4a..d5dfb109dfe1 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -922,6 +922,21 @@ void __kfree_rcu(struct rcu_head *head, unsigned long offset)
kfree_call_rcu(head, (rcu_callback)offset);
}
+/*
+ * Does the specified offset indicate that the corresponding rcu_head
+ * structure can be handled by kfree_rcu()?
+ */
+#define __is_kfree_rcu_offset(offset) ((offset) < 4096)
+
+/*
+ * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
+ */
+#define __kfree_rcu(head, offset) \
+ do { \
+ BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
+ call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \
+ } while (0)
+
/**
* kfree_rcu() - kfree an object after a grace period.
* @ptr: pointer to kfree
@@ -944,6 +959,9 @@ void __kfree_rcu(struct rcu_head *head, unsigned long offset)
*
* Note that the allowable offset might decrease in the future, for example,
* to allow something like kmem_cache_free_rcu().
+ *
+ * The BUILD_BUG_ON check must not involve any function calls, hence the
+ * checks are done in macros here.
*/
#define kfree_rcu(ptr, rcu_head) \
__kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))