Author: rrs
Date: Tue Aug 16 13:08:03 2016
New Revision: 304219
URL: https://svnweb.freebsd.org/changeset/base/304219
Log:
Comments describing how to properly use the new lock_add functions
and its respective companion.
Sponsored by: Netflix Inc.
Modified:
head/sys/netinet/tcp_timer.c
Modified: head/sys/netinet/tcp_timer.c
==============================================================================
--- head/sys/netinet/tcp_timer.c Tue Aug 16 12:40:56 2016
(r304218)
+++ head/sys/netinet/tcp_timer.c Tue Aug 16 13:08:03 2016
(r304219)
@@ -301,6 +301,25 @@ tcp_timer_delack(void *xtp)
CURVNET_RESTORE();
}
+/*
+ * When a timer wants to remove a TCB it must
+ * hold the INP_INFO_RLOCK(). The timer function
+ * should only have grabbed the INP_WLOCK() when
+ * it entered. To safely switch to holding both the
+ * INP_INFO_RLOCK() and the INP_WLOCK() we must first
+ * grab a reference on the inp, this will hold the inp
+ * so that it can't be removed. We then unlock and grab
+ * the info-read lock. Once we have the INP_INFO_RLOCK() we
+ * proceed again to get the INP_WLOCK() but after that
+ * we must check if someone else deleted the pcb i.e.
+ * the inp_flags check. If so we return 1 otherwise
+ * we return 0.
+ *
+ * No matter which the tcp_inpinfo_lock_add() function
+ * returns the caller must afterwards call tcp_inpinfo_lock_del()
+ * to drop the locks and reference properly.
+ */
+
int
tcp_inpinfo_lock_add(struct inpcb *inp)
{
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