ftrace: Remove unused global 'ftrace_direct_func_count'

JIRA: https://issues.redhat.com/browse/RHEL-101598

commit d2cc859
Author: Dr. David Alan Gilbert <linux@treblig.org>
Date:   Tue May 7 00:33:05 2024 +0100

    ftrace: Remove unused global 'ftrace_direct_func_count'

    Commit 8788ca1 ("ftrace: Remove the legacy _ftrace_direct API")
    stopped setting the 'ftrace_direct_func_count' variable, but left
    it around.  Clean it up.

    Link: https://lore.kernel.org/linux-trace-kernel/20240506233305.215735-1-linux@treblig.org

    Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
    Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Conflicts:
- Minor context change due to missing commit d05cb47 ("ftrace:
Fix modification of direct_function hash while in use")

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>

Author: jeromemarchand

include/linux/ftrace.h

@@ -397,7 +397,6 @@ struct ftrace_func_entry {
 };
 
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
-extern int ftrace_direct_func_count;
 unsigned long ftrace_find_rec_direct(unsigned long ip);
 int register_ftrace_direct(struct ftrace_ops *ops, unsigned long addr);
 int unregister_ftrace_direct(struct ftrace_ops *ops, unsigned long addr,
@@ -409,7 +408,6 @@ void ftrace_stub_direct_tramp(void);
 
 #else
 struct ftrace_ops;
-# define ftrace_direct_func_count 0
 static inline unsigned long ftrace_find_rec_direct(unsigned long ip)
 {
 	return 0;

kernel/trace/fgraph.c

@@ -135,17 +135,6 @@ int function_graph_enter(unsigned long ret, unsigned long func,
 {
 	struct ftrace_graph_ent trace;
 
-#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
-	/*
-	 * Skip graph tracing if the return location is served by direct trampoline,
-	 * since call sequence and return addresses are unpredictable anyway.
-	 * Ex: BPF trampoline may call original function and may skip frame
-	 * depending on type of BPF programs attached.
-	 */
-	if (ftrace_direct_func_count &&
-	    ftrace_find_rec_direct(ret - MCOUNT_INSN_SIZE))
-		return -EBUSY;
-#endif
 	trace.func = func;
 	trace.depth = ++current->curr_ret_depth;
 

kernel/trace/ftrace.c

@@ -2533,7 +2533,6 @@ ftrace_find_unique_ops(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