hash: fix tuple adjustment

rte_thash_adjust_tuple() uses random to generate a new subtuple if
fn() callback reports about collision. In some cases random changes
the subtuple in a way that after complementary bits are applied the
original tuple is obtained. This patch replaces random with subtuple
increment.

Fixes: 28ebff11c2dc ("hash: add predictable RSS")
Cc: vladimir.medvedkin@intel.com
Reported-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Vladimir Medvedkin <vladimir.medvedkin@intel.com>
Acked-by: Yipeng Wang <yipeng1.wang@intel.com>
Tested-by: Stanislaw Kardach <kda@semihalf.com>
Reviewed-by: Stanislaw Kardach <kda@semihalf.com>

diff --git a/lib/hash/rte_thash.c b/lib/hash/rte_thash.c
index 135a26d..d5a95a6 100644 (file)
--- a/lib/hash/rte_thash.c
+++ b/lib/hash/rte_thash.c
@@ -610,16 +610,91 @@ rte_thash_get_key(struct rte_thash_ctx *ctx)
        return ctx->hash_key;
 }
 
+static inline uint8_t
+read_unaligned_byte(uint8_t *ptr, unsigned int len, unsigned int offset)
+{
+       uint8_t ret = 0;
+
+       ret = ptr[offset / CHAR_BIT];
+       if (offset % CHAR_BIT) {
+               ret <<= (offset % CHAR_BIT);
+               ret |= ptr[(offset / CHAR_BIT) + 1] >>
+                       (CHAR_BIT - (offset % CHAR_BIT));
+       }
+
+       return ret >> (CHAR_BIT - len);
+}
+
+static inline uint32_t
+read_unaligned_bits(uint8_t *ptr, int len, int offset)
+{
+       uint32_t ret = 0;
+
+       len = RTE_MAX(len, 0);
+       len = RTE_MIN(len, (int)(sizeof(uint32_t) * CHAR_BIT));
+
+       while (len > 0) {
+               ret <<= CHAR_BIT;
+
+               ret |= read_unaligned_byte(ptr, RTE_MIN(len, CHAR_BIT),
+                       offset);
+               offset += CHAR_BIT;
+               len -= CHAR_BIT;
+       }
+
+       return ret;
+}
+
+/* returns mask for len bits with given offset inside byte */
+static inline uint8_t
+get_bits_mask(unsigned int len, unsigned int offset)
+{
+       unsigned int last_bit;
+
+       offset %= CHAR_BIT;
+       /* last bit within byte */
+       last_bit = RTE_MIN((unsigned int)CHAR_BIT, offset + len);
+
+       return ((1 << (CHAR_BIT - offset)) - 1) ^
+               ((1 << (CHAR_BIT - last_bit)) - 1);
+}
+
 static inline void
-xor_bit(uint8_t *ptr, uint32_t bit, uint32_t pos)
+write_unaligned_byte(uint8_t *ptr, unsigned int len,
+       unsigned int offset, uint8_t val)
 {
-       uint32_t byte_idx = pos >> 3;
-       uint32_t bit_idx = (CHAR_BIT - 1) - (pos & (CHAR_BIT - 1));
        uint8_t tmp;
 
-       tmp = ptr[byte_idx];
-       tmp ^= bit << bit_idx;
-       ptr[byte_idx] = tmp;
+       tmp = ptr[offset / CHAR_BIT];
+       tmp &= ~get_bits_mask(len, offset);
+       tmp |= ((val << (CHAR_BIT - len)) >> (offset % CHAR_BIT));
+       ptr[offset / CHAR_BIT] = tmp;
+       if (((offset + len) / CHAR_BIT) != (offset / CHAR_BIT)) {
+               int rest_len = (offset + len) % CHAR_BIT;
+               tmp = ptr[(offset + len) / CHAR_BIT];
+               tmp &= ~get_bits_mask(rest_len, 0);
+               tmp |= val << (CHAR_BIT - rest_len);
+               ptr[(offset + len) / CHAR_BIT] = tmp;
+       }
+}
+
+static inline void
+write_unaligned_bits(uint8_t *ptr, int len, int offset, uint32_t val)
+{
+       uint8_t tmp;
+       unsigned int part_len;
+
+       len = RTE_MAX(len, 0);
+       len = RTE_MIN(len, (int)(sizeof(uint32_t) * CHAR_BIT));
+
+       while (len > 0) {
+               part_len = RTE_MIN(CHAR_BIT, len);
+               tmp = (uint8_t)val & ((1 << part_len) - 1);
+               write_unaligned_byte(ptr, part_len,
+                       offset + len - part_len, tmp);
+               len -= CHAR_BIT;
+               val >>= CHAR_BIT;
+       }
 }
 
 int
@@ -632,8 +707,10 @@ rte_thash_adjust_tuple(struct rte_thash_ctx *ctx,
        uint32_t tmp_tuple[tuple_len / sizeof(uint32_t)];
        unsigned int i, j, ret = 0;
        uint32_t hash, adj_bits;
-       uint8_t bit;
        const uint8_t *hash_key;
+       uint32_t tmp;
+       int offset;
+       int tmp_len;
 
        if ((ctx == NULL) || (h == NULL) || (tuple == NULL) ||
                        (tuple_len % sizeof(uint32_t) != 0) || (attempts <= 0))
@@ -641,6 +718,8 @@ rte_thash_adjust_tuple(struct rte_thash_ctx *ctx,
 
        hash_key = rte_thash_get_key(ctx);
 
+       attempts = RTE_MIN(attempts, 1U << (h->tuple_len - ctx->reta_sz_log));
+
        for (i = 0; i < attempts; i++) {
                for (j = 0; j < (tuple_len / 4); j++)
                        tmp_tuple[j] =
@@ -651,28 +730,28 @@ rte_thash_adjust_tuple(struct rte_thash_ctx *ctx,
 
                /*
                 * Hint: LSB of adj_bits corresponds to
-                * offset + len bit of tuple
+                * offset + len bit of the subtuple
                 */
-               for (j = 0; j < sizeof(uint32_t) * CHAR_BIT; j++) {
-                       bit = (adj_bits >> j) & 0x1;
-                       if (bit)
-                               xor_bit(tuple, bit, h->tuple_offset +
-                                       h->tuple_len - 1 - j);
-               }
+               offset =  h->tuple_offset + h->tuple_len - ctx->reta_sz_log;
+               tmp = read_unaligned_bits(tuple, ctx->reta_sz_log, offset);
+               tmp ^= adj_bits;
+               write_unaligned_bits(tuple, ctx->reta_sz_log, offset, tmp);
 
                if (fn != NULL) {
                        ret = (fn(userdata, tuple)) ? 0 : -EEXIST;
                        if (ret == 0)
                                return 0;
                        else if (i < (attempts - 1)) {
-                               /* Update tuple with random bits */
-                               for (j = 0; j < h->tuple_len; j++) {
-                                       bit = rte_rand() & 0x1;
-                                       if (bit)
-                                               xor_bit(tuple, bit,
-                                                       h->tuple_offset +
-                                                       h->tuple_len - 1 - j);
-                               }
+                               /* increment subtuple part by 1 */
+                               tmp_len = RTE_MIN(sizeof(uint32_t) * CHAR_BIT,
+                                       h->tuple_len - ctx->reta_sz_log);
+                               offset -= tmp_len;
+                               tmp = read_unaligned_bits(tuple, tmp_len,
+                                       offset);
+                               tmp++;
+                               tmp &= (1 << tmp_len) - 1;
+                               write_unaligned_bits(tuple, tmp_len, offset,
+                                       tmp);
                        }
                } else
                        return 0;