[PATCH v3 2/8] lib/vsprintf: Use acquire/release for ptr_key publication

[Jinjie Ruan <ruanjinjie@huawei.com>]

Replace the smp_wmb() + WRITE_ONCE() and READ_ONCE() + smp_rmb() barrier
pair with smp_store_release()/smp_load_acquire() on filled_random_ptr_key.

This expresses the publish/subscribe pattern more clearly and allows
architectures with native acquire/release instructions (e.g. arm64's
STLR/LDAR) to avoid the cost of full one-way barriers (DMB ISHST/ISHLD).

No functional change intended.

Cc: Petr Mladek <pmladek@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Assisted-by: DeepSeek:DeepSeek-V3
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
---
 lib/vsprintf.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 1d95ab9314bf..90d0a724eadd 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -762,9 +762,8 @@ static int fill_ptr_key(struct notifier_block *nb, unsigned long action, void *d
 {
 	get_random_bytes(&ptr_key, sizeof(ptr_key));
 
-	/* Pairs with smp_rmb() before reading ptr_key. */
-	smp_wmb();
-	WRITE_ONCE(filled_random_ptr_key, true);
+	/* Pairs with smp_load_acquire() before reading ptr_key. */
+	smp_store_release(&filled_random_ptr_key, true);
 	return NOTIFY_DONE;
 }
 
@@ -781,12 +780,10 @@ static inline int __ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
 {
 	unsigned long hashval;
 
-	if (!READ_ONCE(filled_random_ptr_key))
+	/* Pairs with smp_store_release() after writing ptr_key. */
+	if (!smp_load_acquire(&filled_random_ptr_key))
 		return -EBUSY;
 
-	/* Pairs with smp_wmb() after writing ptr_key. */
-	smp_rmb();
-
 #ifdef CONFIG_64BIT
 	hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key);
 	/*
-- 
2.34.1