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Note that IFNET_LOCK must not be held in softint

This commit is contained in:
ozaki-r 2017-12-18 08:24:29 +00:00
parent d3007e8218
commit 900df923cc
1 changed files with 11 additions and 1 deletions
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12
sys/net/if.h
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@ -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