ftrace: remove old pointers to mcount

When a mcount pointer is recorded into a table, it is used to add or
remove calls to mcount (replacing them with nops). If the code is removed
via removing a module, the pointers still exist.  At modifying the code
a check is always made to make sure the code being replaced is the code
expected. In-other-words, the code being replaced is compared to what
it is expected to be before being replaced.

There is a very small chance that the code being replaced just happens
to look like code that calls mcount (very small since the call to mcount
is relative). To remove this chance, this patch adds ftrace_release to
allow module unloading to remove the pointers to mcount within the module.

Another change for init calls is made to not trace calls marked with
__init. The tracing can not be started until after init is done anyway.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 4936489f9ed8..6b232a2460c0 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -165,10 +165,12 @@ ftrace_special(unsigned long arg1, unsigned long arg2, unsigned long arg3) { }
 #ifdef CONFIG_FTRACE_MCOUNT_RECORD
 extern void ftrace_init(void);
 extern void ftrace_init_module(unsigned long *start, unsigned long *end);
+extern void ftrace_release(void *start, unsigned long size);
 #else
 static inline void ftrace_init(void) { }
 static inline void
 ftrace_init_module(unsigned long *start, unsigned long *end) { }
+static inline void ftrace_release(void *start, unsigned long size) { }
 #endif
 
 #endif /* _LINUX_FTRACE_H */