linux-kernel - [PATCH] livepatch: Move the result-invariant calculation out of the loop

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Date:   Fri, 30 Sep 2022 09:54:46 +0800
From:   Zhen Lei <thunder.leizhen@...wei.com>
To:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        <live-patching@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     Zhen Lei <thunder.leizhen@...wei.com>
Subject: [PATCH] livepatch: Move the result-invariant calculation out of the loop

The calculation results of the variables 'func_addr' and 'func_size' are
not affected by the for loop and do not change due to the changes of
entries[i]. The performance can be improved by moving it outside the loop.

No functional change.

Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
---
 kernel/livepatch/transition.c | 54 +++++++++++++++++------------------
 1 file changed, 27 insertions(+), 27 deletions(-)

diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index 5d03a2ad1066195..da93aa77715a306 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -196,36 +196,36 @@ static int klp_check_stack_func(struct klp_func *func, unsigned long *entries,
 	struct klp_ops *ops;
 	int i;
 
-	for (i = 0; i < nr_entries; i++) {
-		address = entries[i];
+	if (klp_target_state == KLP_UNPATCHED) {
+		 /*
+		  * Check for the to-be-unpatched function
+		  * (the func itself).
+		  */
+		func_addr = (unsigned long)func->new_func;
+		func_size = func->new_size;
+	} else {
+		/*
+		 * Check for the to-be-patched function
+		 * (the previous func).
+		 */
+		ops = klp_find_ops(func->old_func);
 
-		if (klp_target_state == KLP_UNPATCHED) {
-			 /*
-			  * Check for the to-be-unpatched function
-			  * (the func itself).
-			  */
-			func_addr = (unsigned long)func->new_func;
-			func_size = func->new_size;
+		if (list_is_singular(&ops->func_stack)) {
+			/* original function */
+			func_addr = (unsigned long)func->old_func;
+			func_size = func->old_size;
 		} else {
-			/*
-			 * Check for the to-be-patched function
-			 * (the previous func).
-			 */
-			ops = klp_find_ops(func->old_func);
-
-			if (list_is_singular(&ops->func_stack)) {
-				/* original function */
-				func_addr = (unsigned long)func->old_func;
-				func_size = func->old_size;
-			} else {
-				/* previously patched function */
-				struct klp_func *prev;
-
-				prev = list_next_entry(func, stack_node);
-				func_addr = (unsigned long)prev->new_func;
-				func_size = prev->new_size;
-			}
+			/* previously patched function */
+			struct klp_func *prev;
+
+			prev = list_next_entry(func, stack_node);
+			func_addr = (unsigned long)prev->new_func;
+			func_size = prev->new_size;
 		}
+	}
+
+	for (i = 0; i < nr_entries; i++) {
+		address = entries[i];
 
 		if (address >= func_addr && address < func_addr + func_size)
 			return -EAGAIN;
-- 
2.25.1