compat: backport kfree_rcu()

This adds a nested function everywhere kfree_rcu() was called. This
function frees the memory and is given as a function to call_rcu().
The kfree_rcu define was made by Johannes Berg.
The rcu callback could happen every time also after the module was
unloaded and this will cause problems.
A rcu_barrier() was added into every module_exit so that this will not
be called after the module was unloaded.

The define overwriting module_exit is based on the original module_exit
which looks like this:
/* This is only required if you want to be unloadable. */
/#define module_exit(exitfn)                                    \
        static inline exitcall_t __exittest(void)               \
        { return exitfn; }                                      \
        void cleanup_module(void) __attribute__((alias(#exitfn)));

We replaced the call to the actual function exitfn() with a call to our
function which calls the original exitfn() and then rcu_barrier()

As a module will not be unloaded that ofter it should not have a big
performance impact when rcu_barrier() is called on every module exit,
also when no kfree_rcu() backport is used in that module.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
CC: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Luis R. Rodriguez <mcgrof@qca.qualcomm.com>

diff --git a/include/linux/compat-3.0.h b/include/linux/compat-3.0.h
index 8c8720e0a5fc99e6ff9e7b107953d8d9985a00b4..22ab5399ad12da2084f38a82a19c7f3c35f3e07e 100644 (file)
--- a/include/linux/compat-3.0.h
+++ b/include/linux/compat-3.0.h
@@ -5,6 +5,8 @@
 
 #if (LINUX_VERSION_CODE < KERNEL_VERSION(3,0,0))
 
+#include <linux/rcupdate.h>
+
 /*
  * since commit 1c5cae815d19ffe02bdfda1260949ef2b1806171
  * "net: call dev_alloc_name from register_netdevice" dev_alloc_name is
@@ -79,6 +81,50 @@ static inline int __must_check kstrtos32_from_user(const char __user *s, size_t
        return kstrtoint_from_user(s, count, base, res);
 }
 
+/* 
+ * This adds a nested function everywhere kfree_rcu() was called. This
+ * function frees the memory and is given as a function to call_rcu().
+ * The rcu callback could happen every time also after the module was
+ *  unloaded and this will cause problems.
+ */
+#define kfree_rcu(data, rcuhead)               do {                    \
+               void __kfree_rcu_fn(struct rcu_head *rcu_head)          \
+               {                                                       \
+                       void *___ptr;                                   \
+                       ___ptr = container_of(rcu_head, typeof(*(data)), rcuhead);\
+                       kfree(___ptr);                                  \
+               }                                                       \
+               call_rcu(&(data)->rcuhead, __kfree_rcu_fn);             \
+       } while (0)
+
+#ifdef MODULE
+
+/*
+ * The define overwriting module_exit is based on the original module_exit
+ * which looks like this:
+ * #define module_exit(exitfn)                                    \
+ *         static inline exitcall_t __exittest(void)               \
+ *         { return exitfn; }                                      \
+ *         void cleanup_module(void) __attribute__((alias(#exitfn)));
+ *
+ * We replaced the call to the actual function exitfn() with a call to our
+ * function which calls the original exitfn() and then rcu_barrier()
+ *
+ * As a module will not be unloaded that ofter it should not have a big
+ * performance impact when rcu_barrier() is called on every module exit,
+ * also when no kfree_rcu() backport is used in that module.
+ */
+#undef module_exit
+#define module_exit(exitfn)                                            \
+       static void __exit __exit_compat(void)                          \
+       {                                                               \
+               exitfn();                                               \
+               rcu_barrier();                                          \
+       }                                                               \
+       void cleanup_module(void) __attribute__((alias("__exit_compat")));
+
+#endif
+
 #endif /* (LINUX_VERSION_CODE < KERNEL_VERSION(3,0,0)) */
 
 #endif /* LINUX_3_0_COMPAT_H */