x86/ftrace: fix boot time slowdown

Commit Message

Mike Rapoport Nov. 24, 2024, 2:07 p.m. UTC

From: "Mike Rapoport (Microsoft)" <[e-mail]>

Steven Rostedt reported slowdown by over 30ms caused by commit 9bfc4824fd48
("x86/module: prepare module loading for ROX allocations of text")

  Before:

   # cat /sys/kernel/tracing/dyn_ftrace_total_info
  57695 pages:231 groups: 9
  ftrace boot update time = 14733459 (ns)
  ftrace module total update time = 449016 (ns)

  After:

   # cat /sys/kernel/tracing/dyn_ftrace_total_info
  57708 pages:231 groups: 9
  ftrace boot update time = 47195374 (ns)
  ftrace module total update time = 592080 (ns)

The slowdown happened because initial patching of kernel code for ftrace
was switched from text_poke_early() to text_poke() to accommodate ftrace
updates of module text allocated as ROX.

Restore the use of text_poke_early() for boot time patching of the kernel
code.

Reported-by: Steven Rostedt <[e-mail]>
Closes: https://lore.kernel.org/all/[e-mail]
Fixes: 9bfc4824fd48 ("x86/module: prepare module loading for ROX allocations of text")
Signed-off-by: Mike Rapoport (Microsoft) <[e-mail]>
---
 arch/x86/kernel/ftrace.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)


base-commit: 9f16d5e6f220661f73b36a4be1b21575651d8833

Patch

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 4dd0ad6c94d6..9e50288abbaa 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -111,7 +111,7 @@  static int ftrace_verify_code(unsigned long ip, const char *old_code)
  */
 static int __ref
 ftrace_modify_code_direct(unsigned long ip, const char *old_code,
-			  const char *new_code)
+			  const char *new_code, struct module *mod)
 {
 	int ret = ftrace_verify_code(ip, old_code);
 	if (ret)
@@ -120,6 +120,8 @@  ftrace_modify_code_direct(unsigned long ip, const char *old_code,
 	/* replace the text with the new text */
 	if (ftrace_poke_late) {
 		text_poke_queue((void *)ip, new_code, MCOUNT_INSN_SIZE, NULL);
+	} else if (!mod) {
+		text_poke_early((void *)ip, new_code, MCOUNT_INSN_SIZE);
 	} else {
 		mutex_lock(&text_mutex);
 		text_poke((void *)ip, new_code, MCOUNT_INSN_SIZE);
@@ -145,7 +147,7 @@  int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long ad
 	 * just modify the code directly.
 	 */
 	if (addr == MCOUNT_ADDR)
-		return ftrace_modify_code_direct(ip, old, new);
+		return ftrace_modify_code_direct(ip, old, new, mod);
 
 	/*
 	 * x86 overrides ftrace_replace_code -- this function will never be used
@@ -164,7 +166,7 @@  int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 	new = ftrace_call_replace(ip, addr);
 
 	/* Should only be called when module is loaded */
-	return ftrace_modify_code_direct(rec->ip, old, new);
+	return ftrace_modify_code_direct(rec->ip, old, new, NULL);
 }
 
 /*