Author: rwatson
Date: Sun Mar 7 14:13:59 2010
New Revision: 204829
URL: http://svn.freebsd.org/changeset/base/204829
Log:
Add comment in tcp_discardcb() talking about how we don't, but should,
address TCP races relating to not calling tcp_drain() on stopped callouts.
Discussed with: bz
Modified:
head/sys/netinet/tcp_subr.c
Modified: head/sys/netinet/tcp_subr.c
==============================================================================
--- head/sys/netinet/tcp_subr.c Sun Mar 7 12:41:42 2010 (r204828)
+++ head/sys/netinet/tcp_subr.c Sun Mar 7 14:13:59 2010 (r204829)
@@ -835,8 +835,19 @@ tcp_discardcb(struct tcpcb *tp)
INP_WLOCK_ASSERT(inp);
/*
- * Make sure that all of our timers are stopped before we
- * delete the PCB.
+ * Make sure that all of our timers are stopped before we delete the
+ * PCB.
+ *
+ * XXXRW: Really, we would like to use callout_drain() here in order
+ * to avoid races experienced in tcp_timer.c where a timer is already
+ * executing at this point. However, we can't, both because we're
+ * running in a context where we can't sleep, and also because we
+ * hold locks required by the timers. What we instead need to do is
+ * test to see if callout_drain() is required, and if so, defer some
+ * portion of the remainder of tcp_discardcb() to an asynchronous
+ * context that can callout_drain() and then continue. Some care
+ * will be required to ensure that no further processing takes place
+ * on the tcpcb, even though it hasn't been freed (a flag?).
*/
callout_stop(&tp->t_timers->tt_rexmt);
callout_stop(&tp->t_timers->tt_persist);
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