From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Fri, 29 Jul 2022 15:52:45 +0200
Subject: [PATCH 1/2] lib/vsprintf: Remove static_branch_likely() from
 __ptr_to_hashval().

Using static_branch_likely() to signal that ptr_key has been filled is a
bit much given that it is not a fast path.

Replace static_branch_likely() with bool for condition and a memory
barrier for ptr_key.

Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lkml.kernel.org/r/20220729154716.429964-2-bigeasy@linutronix.de
---
 lib/vsprintf.c |   19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -750,12 +750,7 @@ static int __init debug_boot_weak_hash_e
 }
 early_param("debug_boot_weak_hash", debug_boot_weak_hash_enable);
 
-static DEFINE_STATIC_KEY_FALSE(filled_random_ptr_key);
-
-static void enable_ptr_key_workfn(struct work_struct *work)
-{
-	static_branch_enable(&filled_random_ptr_key);
-}
+static bool filled_random_ptr_key;
 
 /* Maps a pointer to a 32 bit unique identifier. */
 static inline int __ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
@@ -763,24 +758,26 @@ static inline int __ptr_to_hashval(const
 	static siphash_key_t ptr_key __read_mostly;
 	unsigned long hashval;
 
-	if (!static_branch_likely(&filled_random_ptr_key)) {
+	if (!READ_ONCE(filled_random_ptr_key)) {
 		static bool filled = false;
 		static DEFINE_SPINLOCK(filling);
-		static DECLARE_WORK(enable_ptr_key_work, enable_ptr_key_workfn);
 		unsigned long flags;
 
-		if (!system_unbound_wq || !rng_is_initialized() ||
+		if (!rng_is_initialized() ||
 		    !spin_trylock_irqsave(&filling, flags))
 			return -EAGAIN;
 
 		if (!filled) {
 			get_random_bytes(&ptr_key, sizeof(ptr_key));
-			queue_work(system_unbound_wq, &enable_ptr_key_work);
+			/* Pairs with smp_rmb() before reading ptr_key. */
+			smp_wmb();
+			WRITE_ONCE(filled_random_ptr_key, true);
 			filled = true;
 		}
 		spin_unlock_irqrestore(&filling, flags);
 	}
-
+	/* Pairs with smp_wmb() after writing ptr_key. */
+	smp_rmb();
 
 #ifdef CONFIG_64BIT
 	hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key);