Signed-off-by: Hauke Mehrtens <hauke@xxxxxxxxxx>
---
include/linux/compat-2.6.40.h | 60 +++++++++++++++++++++++++++++++++++++++++
1 files changed, 60 insertions(+), 0 deletions(-)
diff --git a/include/linux/compat-2.6.40.h b/include/linux/compat-2.6.40.h
index 42f9fee..9ec8c1b 100644
--- a/include/linux/compat-2.6.40.h
+++ b/include/linux/compat-2.6.40.h
@@ -5,6 +5,8 @@
#if (LINUX_VERSION_CODE < KERNEL_VERSION(2,6,40))
+#include <linux/rcupdate.h>
+
/*
* This is not part of The 2.6.37 kernel yet but we
* we use it to optimize the backport code we
@@ -22,6 +24,64 @@
#define br_port_exists(dev) (dev->br_port)
#endif
+static __always_inline bool __is_kfree_rcu_offset(unsigned long offset)
+{
+ return offset < 4096;
+}
+
+static __always_inline
+void __kfree_rcu(struct rcu_head *head, unsigned long offset)
+{
+ typedef void (*rcu_callback)(struct rcu_head *);
+
+ /* This causes build failures with some kernel versions at positions
+ * where this methods is not used at all.
+ */
+ /* BUILD_BUG_ON(!__builtin_constant_p(offset)); */
+
+ /* See the kfree_rcu() header comment. */
+ /* BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); */
+
+ call_rcu(head, (rcu_callback)offset);
+}
+
+static inline void __rcu_reclaim(struct rcu_head *head)
+{
+ unsigned long offset = (unsigned long)head->func;
+
+ if (__is_kfree_rcu_offset(offset))
+ kfree((void *)head - offset);
+ else
+ head->func(head);
+}
+
+/**
+ * kfree_rcu() - kfree an object after a grace period.
+ * @ptr: pointer to kfree
+ * @rcu_head: the name of the struct rcu_head within the type of @ptr.
+ *
+ * Many rcu callbacks functions just call kfree() on the base structure.
+ * These functions are trivial, but their size adds up, and furthermore
+ * when they are used in a kernel module, that module must invoke the
+ * high-latency rcu_barrier() function at module-unload time.
+ *
+ * The kfree_rcu() function handles this issue. Rather than encoding a
+ * function address in the embedded rcu_head structure, kfree_rcu() instead
+ * encodes the offset of the rcu_head structure within the base structure.
+ * Because the functions are not allowed in the low-order 4096 bytes of
+ * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
+ * If the offset is larger than 4095 bytes, a compile-time error will
+ * be generated in __kfree_rcu(). If this error is triggered, you can
+ * either fall back to use of call_rcu() or rearrange the structure to
+ * position the rcu_head structure into the first 4096 bytes.
+ *
+ * Note that the allowable offset might decrease in the future, for example,
+ * to allow something like kmem_cache_free_rcu().
+ */
+#define kfree_rcu(ptr, rcu_head) \
+ __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
+
+
#endif /* (LINUX_VERSION_CODE < KERNEL_VERSION(2,6,40)) */
#endif /* LINUX_26_40_COMPAT_H */
--
1.7.4.1
--
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