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random: simplify arithmetic function flow in account() 

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>
This commit is contained in:
Jason A. Donenfeld 2022-01-17 18:43:02 +01:00
parent 248045b8de
commit a254a0e409
1 changed files with 6 additions and 11 deletions
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17
drivers/char/random.c
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@ -1293,7 +1293,7 @@ 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);
@ -1301,20 +1301,15 @@ static size_t account(size_t nbytes, int min)
/* 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;