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* [dpdk-dev] [memnic PATCH 1/5] pmd: fix race condition
@ 2014-03-11  5:37 Hiroshi Shimamoto
  2014-03-26 16:44 ` Olivier MATZ
  0 siblings, 1 reply; 4+ messages in thread
From: Hiroshi Shimamoto @ 2014-03-11  5:37 UTC (permalink / raw)
  To: dev; +Cc: Hayato Momma

From: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>

There is a race condition, on transmit to vSwitch.

Guest PMD                 Host
Thread-A     Thread-B     vSwitch
   |idx=0       |idx=0       |p[0] st!=2
   |cmpxchg     |            |
   |p[0] st->1  |            |
   |idx=1       |            |
   |fill data   |            |
   |p[0] st->2  |            |p[0] st==2
   |            |            |receive data
   |            |            |p[0] st->0
   |            |cmpxchg     |
   |            |success     |p[1] st!=2
   |            |p[0] st->1  |
                  This is BAD

That causes traffic stop.

We have to take care about that race condition with checking
whether current index is correct.

Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Reviewed-by: Hayato Momma <h-momma@ce.jp.nec.com>
---
 pmd/pmd_memnic.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/pmd/pmd_memnic.c b/pmd/pmd_memnic.c
index 30d5a1b..805f0b2 100644
--- a/pmd/pmd_memnic.c
+++ b/pmd/pmd_memnic.c
@@ -278,6 +278,15 @@ retry:
 			goto retry;
 		}
 
+		if (idx != ACCESS_ONCE(adapter->down_idx)) {
+			/*
+			 * vSwitch freed this and got false positive,
+			 * need to recover the status and retry.
+			 */
+			p->status = MEMNIC_PKT_ST_FREE;
+			goto retry;
+		}
+
 		if (++idx >= MEMNIC_NR_PACKET)
 			idx = 0;
 		adapter->down_idx = idx;
-- 
1.8.4

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2014-03-28 14:42 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2014-03-11  5:37 [dpdk-dev] [memnic PATCH 1/5] pmd: fix race condition Hiroshi Shimamoto
2014-03-26 16:44 ` Olivier MATZ
2014-03-28  9:49   ` Hiroshi Shimamoto
2014-03-28 14:43     ` Thomas Monjalon

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