linux-kernel - [PATCH 4.9 015/264] random: reorder READ_ONCE() in get_random

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Message-Id: <20220623164344.496193971@linuxfoundation.org>
Date:   Thu, 23 Jun 2022 18:40:08 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, "Jason A. Donenfeld" <Jason@...c4.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Theodore Tso <tytso@....edu>
Subject: [PATCH 4.9 015/264] random: reorder READ_ONCE() in get_random_uXX

From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

commit 72e5c740f6335e27253b8ff64d23d00337091535 upstream.

Avoid the READ_ONCE in commit 4a072c71f49b ("random: silence compiler
warnings and fix race") if we can leave the function after
arch_get_random_XXX().

Cc: Jason A. Donenfeld <Jason@...c4.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/char/random.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -2161,7 +2161,7 @@ static DEFINE_PER_CPU(struct batched_ent
 u64 get_random_u64(void)
 {
 	u64 ret;
-	bool use_lock = READ_ONCE(crng_init) < 2;
+	bool use_lock;
 	unsigned long flags = 0;
 	struct batched_entropy *batch;
 	static void *previous;
@@ -2177,6 +2177,7 @@ u64 get_random_u64(void)
 
 	warn_unseeded_randomness(&previous);
 
+	use_lock = READ_ONCE(crng_init) < 2;
 	batch = &get_cpu_var(batched_entropy_u64);
 	if (use_lock)
 		read_lock_irqsave(&batched_entropy_reset_lock, flags);
@@ -2196,7 +2197,7 @@ static DEFINE_PER_CPU(struct batched_ent
 u32 get_random_u32(void)
 {
 	u32 ret;
-	bool use_lock = READ_ONCE(crng_init) < 2;
+	bool use_lock;
 	unsigned long flags = 0;
 	struct batched_entropy *batch;
 	static void *previous;
@@ -2206,6 +2207,7 @@ u32 get_random_u32(void)
 
 	warn_unseeded_randomness(&previous);
 
+	use_lock = READ_ONCE(crng_init) < 2;
 	batch = &get_cpu_var(batched_entropy_u32);
 	if (use_lock)
 		read_lock_irqsave(&batched_entropy_reset_lock, flags);