[PATCH 4.9 106/264] random: simplify arithmetic function flow in account()

Greg Kroah-Hartman
2022-06-23T16:52:42Z

From: "Jason A. Donenfeld" <Jason@zx2c4.com>

commit a254a0e4093fce8c832414a83940736067eed515 upstream.

Now that have_bytes is never modified, we can simplify this function.
First, we move the check for negative entropy_count to be first. That
ensures that subsequent reads of this will be non-negative. Then,
have_bytes and ibytes can be folded into their one use site in the
min_t() function.

Suggested-by: Dominik Brodowski <linux@dominikbrodowski.net>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 17 ++++++-----------
1 file changed, 6 insertions(+), 11 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1344,7 +1344,7 @@ EXPORT_SYMBOL_GPL(add_disk_randomness);
*/
static size_t account(size_t nbytes, int min)
{
- int entropy_count, orig, have_bytes;
+ int entropy_count, orig;
size_t ibytes, nfrac;

BUG_ON(input_pool.entropy_count > POOL_FRACBITS);
@@ -1352,20 +1352,15 @@ static size_t account(size_t nbytes, int
/* Can we pull enough? */
retry:
entropy_count = orig = READ_ONCE(input_pool.entropy_count);
- ibytes = nbytes;
- /* never pull more than available */
- have_bytes = entropy_count >> (POOL_ENTROPY_SHIFT + 3);
-
- if (have_bytes < 0)
- have_bytes = 0;
- ibytes = min_t(size_t, ibytes, have_bytes);
- if (ibytes < min)
- ibytes = 0;
-
if (WARN_ON(entropy_count < 0)) {
pr_warn("negative entropy count: count %d\n", entropy_count);
entropy_count = 0;
}
+
+ /* never pull more than available */
+ ibytes = min_t(size_t, nbytes, entropy_count >> (POOL_ENTROPY_SHIFT + 3));
+ if (ibytes < min)
+ ibytes = 0;
nfrac = ibytes << (POOL_ENTROPY_SHIFT + 3);
if ((size_t)entropy_count > nfrac)
entropy_count -= nfrac;