On Fri, 28 Jun 2019, Steven Rostedt wrote:

quoted

quoted

quoted

How is that supposed to work?

    ftrace  	     	
	prepare()
	 setrw()
			setro()
	patch <- FAIL  

/me dodges frozen shark

You are right of course.  My brain has apparently already shut off for
the day.

Maybe a comment or two would help though.  

I'd actually prefer (perhaps in parallel to the comment) using the 
__acquires() and __releases() anotations, so that sparse and friends don't 
get confused by that either.

Care to send a patch? :-)

From: Jiri Kosina <redacted>
Subject: [PATCH] ftrace/x86: anotate text_mutex split between ftrace_arch_code_modify_post_process() and ftrace_arch_code_modify_prepare()

ftrace_arch_code_modify_prepare() is acquiring text_mutex, while the 
corresponding release is happening in ftrace_arch_code_modify_post_process().

This has already been documented in the code, but let's also make the fact 
that this is intentional clear to the semantic analysis tools such as 
sparse.

Fixes: 39611265edc1a ("ftrace/x86: Add a comment to why we take text_mutex in ftrace_arch_code_modify_prepare()")
Fixes: d5b844a2cf507 ("ftrace/x86: Remove possible deadlock between register_kprobe() and ftrace_run_update_code()")
Signed-off-by: Jiri Kosina <redacted>
---
 arch/x86/kernel/ftrace.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index d7e93b2783fd..76228525acd0 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c

@@ -35,6 +35,7 @@
 #ifdef CONFIG_DYNAMIC_FTRACE
 
 int ftrace_arch_code_modify_prepare(void)
+    __acquires(&text_mutex)
 {
 	/*
 	 * Need to grab text_mutex to prevent a race from module loading

@@ -48,6 +49,7 @@ int ftrace_arch_code_modify_prepare(void)
 }
 
 int ftrace_arch_code_modify_post_process(void)
+    __releases(&text_mutex)
 {
 	set_all_modules_text_ro();
 	set_kernel_text_ro();

-- 
Jiri Kosina
SUSE Labs