[PATCH 2/2] ANDROID: cfi: free old cfi shadow asynchronously

From: Haibo Li
Date: Thu Jun 30 2022 - 05:47:22 EST


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

diff --git a/kernel/cfi.c b/kernel/cfi.c
index 456771c8e454..a4836d59ca27 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 _cfi_shadow_free_rcu(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, _cfi_shadow_free_rcu);
}
}

--
2.25.1