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

Author: Frank Sorenson <sorenson@redhat.com>
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 << 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 <sorenson@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

diff --git a/net/sunrpc/auth.c b/net/sunrpc/auth.c
index 696eb39..a7e42f9 100644 (file)
--- 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;