sunrpc: Fix bit count when setting hashtable size to power-of-two

fsorenson · trondmypd · commit 34ae685cb3ac · 2016-07-19T16:23:26.000-04:00
Author: Frank Sorenson &lt;sorenson@redhat.com&gt;
Date:   2016-06-27 13:55:48 -0500

    sunrpc: Fix bit count when setting hashtable size to power-of-two

    The hashtable size is incorrectly calculated as the next higher
    power-of-two when being set to a power-of-two.  fls() returns the
    bit number of the most significant set bit, with the least
    significant bit being numbered '1'.  For a power-of-two, fls()
    will return a bit number which is one higher than the number of bits
    required, leading to a hashtable which is twice the requested size.

    In addition, the value of (1 &lt;&lt; nbits) will always be at least num,
    so the test will never be true.

    Fix the hash table size calculation to correctly set hashtable
    size, and eliminate the unnecessary check.

    Signed-off-by: Frank Sorenson &lt;sorenson@redhat.com&gt;

Signed-off-by: Trond Myklebust &lt;trond.myklebust@primarydata.com&gt;
diff --git a/net/sunrpc/auth.c b/net/sunrpc/auth.c
@@ -51,9 +51,7 @@ static int param_set_hashtbl_sz(const char *val, const struct kernel_param *kp)
 	ret = kstrtoul(val, 0, &num);
 	if (ret == -EINVAL)
 		goto out_inval;
-	nbits = fls(num);
-	if (num > (1U << nbits))
-		nbits++;
+	nbits = fls(num - 1);
 	if (nbits > MAX_HASHTABLE_BITS || nbits < 2)
 		goto out_inval;
 	*(unsigned int *)kp->arg = nbits;
