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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().
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.0/older/patches-6.0.5-rt14.tar.xz
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);
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