Module Name: src
Committed By: ozaki-r
Date: Mon Dec 18 08:24:29 UTC 2017
Modified Files:
src/sys/net: if.h
Log Message:
Note that IFNET_LOCK must not be held in softint
To generate a diff of this commit:
cvs rdiff -u -r1.256 -r1.257 src/sys/net/if.h
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/net/if.h
diff -u src/sys/net/if.h:1.256 src/sys/net/if.h:1.257
--- src/sys/net/if.h:1.256 Fri Dec 15 04:07:20 2017
+++ src/sys/net/if.h Mon Dec 18 08:24:29 2017
@@ -1,4 +1,4 @@
-/* $NetBSD: if.h,v 1.256 2017/12/15 04:07:20 ozaki-r Exp $ */
+/* $NetBSD: if.h,v 1.257 2017/12/18 08:24:29 ozaki-r Exp $ */
/*-
* Copyright (c) 1999, 2000, 2001 The NetBSD Foundation, Inc.
@@ -448,6 +448,16 @@ typedef struct ifnet {
* - Must be updated with holding IFNET_LOCK
* - You cannot use the flag in Tx/Rx paths anymore because there is no
* synchronization on the flag except for IFNET_LOCK
+ * - Note that IFNET_LOCK can't be taken in softint because it's known
+ * that it causes a deadlock
+ * - Some synchronization mechanisms such as pserialize_perform are called
+ * with IFNET_LOCK and also require context switches on every CPUs
+ * that mean softints finish so trying to take IFNET_LOCK in softint
+ * might block on IFNET_LOCK and prevent such synchronization mechanisms
+ * from being completed
+ * - Currently the deadlock occurs only if NET_MPSAFE is enabled, however,
+ * we should deal with the restriction because NET_MPSAFE will be enabled
+ * by default in the future
* - if_watchdog and if_timer
* - The watchdog framework works only for non-IFEF_MPSAFE interfaces
* that rely on KERNEL_LOCK
