[PATCH 4.9 015/264] random: reorder READ_ONCE() in get_random_uXX

Greg Kroah-Hartman
2022-06-23T16:46:06Z

From: Sebastian Andrzej Siewior <bigeasy@linutronix.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@zx2c4.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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);