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ftrace/x86: Add a counter to test function_graph with direct 

As testing for direct calls from the function graph tracer adds a little
overhead (which is a lot when tracing every function), add a counter that
can be used to test if function_graph tracer needs to test for a direct
caller or not.

It would have been nicer if we could use a static branch, but the static
branch logic fails when used within the function graph tracer trampoline.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (VMware) 2019-11-08 13:12:57 -05:00
parent 562955fe6a
commit a3ad1a7e39
3 changed files with 11 additions and 3 deletions
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8
arch/x86/kernel/ftrace.c
View File

@ -1049,9 +1049,11 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
* return address is actually off by one word, and we
* need to adjust for that.
*/
if (ftrace_find_direct_func(self_addr + MCOUNT_INSN_SIZE)) {
self_addr = *parent;
parent++;
if (ftrace_direct_func_count) {
if (ftrace_find_direct_func(self_addr + MCOUNT_INSN_SIZE)) {
self_addr = *parent;
parent++;
}
}
/*

2
include/linux/ftrace.h
View File

@ -247,10 +247,12 @@ static inline void ftrace_free_mem(struct module *mod, void *start, void *end) {
#endif /* CONFIG_FUNCTION_TRACER */
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
extern int ftrace_direct_func_count;
int register_ftrace_direct(unsigned long ip, unsigned long addr);
int unregister_ftrace_direct(unsigned long ip, unsigned long addr);
struct ftrace_direct_func *ftrace_find_direct_func(unsigned long addr);
#else
# define ftrace_direct_func_count 0
static inline int register_ftrace_direct(unsigned long ip, unsigned long addr)
{
return -ENODEV;

4
kernel/trace/ftrace.c
View File

@ -2364,6 +2364,7 @@ ftrace_find_tramp_ops_new(struct dyn_ftrace *rec)
/* Protected by rcu_tasks for reading, and direct_mutex for writing */
static struct ftrace_hash *direct_functions = EMPTY_HASH;
static DEFINE_MUTEX(direct_mutex);
int ftrace_direct_func_count;
/*
* Search the direct_functions hash to see if the given instruction pointer
@ -5056,6 +5057,7 @@ int register_ftrace_direct(unsigned long ip, unsigned long addr)
direct->addr = addr;
direct->count = 0;
list_add_rcu(&direct->next, &ftrace_direct_funcs);
ftrace_direct_func_count++;
}
entry->ip = ip;
@ -5081,6 +5083,7 @@ int register_ftrace_direct(unsigned long ip, unsigned long addr)
if (free_hash)
free_ftrace_hash(free_hash);
free_hash = NULL;
ftrace_direct_func_count--;
}
} else {
if (!direct->count)
@ -5141,6 +5144,7 @@ int unregister_ftrace_direct(unsigned long ip, unsigned long addr)
list_del_rcu(&direct->next);
synchronize_rcu_tasks();
kfree(direct);
ftrace_direct_func_count--;
}
}
out_unlock: