linux-kernel - [PATCH v2 2/2] cfi: free old cfi shadow asynchronously

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Date:   Mon, 4 Jul 2022 09:40:46 +0800
From:   Haibo Li <haibo.li@...iatek.com>
To:     Sami Tolvanen <samitolvanen@...gle.com>
CC:     <xiaoming.yu@...iatek.com>, Kees Cook <keescook@...omium.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        André Almeida <andrealmeid@...lia.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Haibo Li <haibo.li@...iatek.com>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Aaron Tomlin <atomlin@...hat.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        <linux-kernel@...r.kernel.org>, <llvm@...ts.linux.dev>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        Lecopzer Chen <lecopzer.chen@...iatek.com>
Subject: [PATCH v2 2/2] cfi: free old cfi shadow asynchronously

Currenly, it uses synchronize_rcu() to wait old rcu reader to go away
in update_shadow.In embedded platform like ARM CA7X,
load_module blocks 40~50ms in update_shadow.
When there are more than one hundred kernel modules,
it blocks several seconds.

To accelerate load_module,change synchronize_rcu to call_rcu.

Signed-off-by: Haibo Li <haibo.li@...iatek.com>
Signed-off-by: Lecopzer Chen <lecopzer.chen@...iatek.com>
---
 kernel/cfi.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/kernel/cfi.c b/kernel/cfi.c
index 6c8ae07b5835..f61439392bf8 100644
--- a/kernel/cfi.c
+++ b/kernel/cfi.c
@@ -43,6 +43,8 @@ typedef u16 shadow_t;
 struct cfi_shadow {
 	/* Page index for the beginning of the shadow */
 	unsigned long base;
+	/* rcu to free old cfi_shadow asynchronously */
+	struct rcu_head rcu;
 	/* An array of __cfi_check locations (as indices to the shadow) */
 	shadow_t shadow[1];
 } __packed;
@@ -182,6 +184,13 @@ static void remove_module_from_shadow(struct cfi_shadow *s, struct module *mod,
 	}
 }
 
+static void free_shadow(struct rcu_head *rcu)
+{
+	struct cfi_shadow *old = container_of(rcu, struct cfi_shadow, rcu);
+
+	vfree(old);
+}
+
 typedef void (*update_shadow_fn)(struct cfi_shadow *, struct module *,
 			unsigned long min_addr, unsigned long max_addr);
 
@@ -211,11 +220,10 @@ static void update_shadow(struct module *mod, unsigned long base_addr,
 
 	rcu_assign_pointer(cfi_shadow, next);
 	mutex_unlock(&shadow_update_lock);
-	synchronize_rcu();
 
 	if (prev) {
 		set_memory_rw((unsigned long)prev, SHADOW_PAGES);
-		vfree(prev);
+		call_rcu(&prev->rcu, free_shadow);
 	}
 }
 
-- 
2.25.1