linux-kernel - [PATCH 2/3] static_call: Align static_call_is

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Message-ID: <20210318113610.636651340@infradead.org>
Date:   Thu, 18 Mar 2021 12:31:58 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org, jpoimboe@...hat.com, jbaron@...mai.com,
        rostedt@...dmis.org, ardb@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        sumit.garg@...aro.org, oliver.sang@...el.com, jarkko@...nel.org
Subject: [PATCH 2/3] static_call: Align static_call_is_init() patching condition

The intent is to avoid writing init code after init (because the text
might have been freed). The code is needlessly different between
jump_label and static_call and not obviously correct.

The existing code relies on the fact that the module loader clears the
init layout, such that within_module_init() always fails, while
jump_label relies on the module state which is more obvious and
matches the kernel logic.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/static_call.c |   14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

--- a/kernel/static_call.c
+++ b/kernel/static_call.c
@@ -149,6 +149,7 @@ void __static_call_update(struct static_
 	};
 
 	for (site_mod = &first; site_mod; site_mod = site_mod->next) {
+		bool init = system_state < SYSTEM_RUNNING;
 		struct module *mod = site_mod->mod;
 
 		if (!site_mod->sites) {
@@ -168,6 +169,7 @@ void __static_call_update(struct static_
 		if (mod) {
 			stop = mod->static_call_sites +
 			       mod->num_static_call_sites;
+			init = mod->state == MODULE_STATE_COMING;
 		}
 #endif
 
@@ -175,16 +177,8 @@ void __static_call_update(struct static_
 		     site < stop && static_call_key(site) == key; site++) {
 			void *site_addr = static_call_addr(site);
 
-			if (static_call_is_init(site)) {
-				/*
-				 * Don't write to call sites which were in
-				 * initmem and have since been freed.
-				 */
-				if (!mod && system_state >= SYSTEM_RUNNING)
-					continue;
-				if (mod && !within_module_init((unsigned long)site_addr, mod))
-					continue;
-			}
+			if (!init && static_call_is_init(site))
+				continue;
 
 			if (!kernel_text_address((unsigned long)site_addr)) {
 				WARN_ONCE(1, "can't patch static call site at %pS",