Eric Lee / smarc-fsl-linux-kernel

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Commit f9c2ff22bb2df7b8f153afd2a4bea07176bad144

Authored by Eric Dumazet
Committed by David S. Miller
1 parent 1edaa7e8a7

net: tcp: dctcp_update_alpha() fixes. 

dctcp_alpha can be read by from dctcp_get_info() without
synchro, so use WRITE_ONCE() to prevent compiler from using
dctcp_alpha as a temporary variable.

Also, playing with small dctcp_shift_g (like 1), can expose
an overflow with 32bit values shifted 9 times before divide.

Use an u64 field to avoid this problem, and perform the divide
only if acked_bytes_ecn is not zero.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Showing 1 changed file with 16 additions and 10 deletions Side-by-side Diff

net/ipv4/tcp_dctcp.c
Diff comments   View file @ f9c2ff2
... ... @@ -204,20 +204,26 @@
204 204  
205 205 /* Expired RTT */
206 206 if (!before(tp->snd_una, ca->next_seq)) {
207   - /* For avoiding denominator == 1. */
208   - if (ca->acked_bytes_total == 0)
209   - ca->acked_bytes_total = 1;
  207 + u64 bytes_ecn = ca->acked_bytes_ecn;
  208 + u32 alpha = ca->dctcp_alpha;
210 209  
211 210 /* alpha = (1 - g) * alpha + g * F */
212   - ca->dctcp_alpha = ca->dctcp_alpha -
213   - (ca->dctcp_alpha >> dctcp_shift_g) +
214   - (ca->acked_bytes_ecn << (10U - dctcp_shift_g)) /
215   - ca->acked_bytes_total;
216 211  
217   - if (ca->dctcp_alpha > DCTCP_MAX_ALPHA)
218   - /* Clamp dctcp_alpha to max. */
219   - ca->dctcp_alpha = DCTCP_MAX_ALPHA;
  212 + alpha -= alpha >> dctcp_shift_g;
  213 + if (bytes_ecn) {
  214 + /* If dctcp_shift_g == 1, a 32bit value would overflow
  215 + * after 8 Mbytes.
  216 + */
  217 + bytes_ecn <<= (10 - dctcp_shift_g);
  218 + do_div(bytes_ecn, max(1U, ca->acked_bytes_total));
220 219  
  220 + alpha = min(alpha + (u32)bytes_ecn, DCTCP_MAX_ALPHA);
  221 + }
  222 + /* dctcp_alpha can be read from dctcp_get_info() without
  223 + * synchro, so we ask compiler to not use dctcp_alpha
  224 + * as a temporary variable in prior operations.
  225 + */
  226 + WRITE_ONCE(ca->dctcp_alpha, alpha);
221 227 dctcp_reset(tp, ca);
222 228 }
223 229 }