[PATCH] When rtnl_trylock failed, wait a time to start another try; It can avoid the dead lock caused by the priority reverse
From: Xianpeng Zhao <hidden>
Date: 2016-02-17 08:23:16
Subsystem:
networking [general], networking [ipv4/ipv6], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, David Ahern, Ido Schimmel, Linus Torvalds
Hi, I have find a problem in my system, I found there have a chance that cause the system enter dead loop when try to get the rtnl lock in the sysctl function in net/ipv6/addrconf.c The situation should like this, there are 2 processes may need get the rtnl lock, we call them process A and process B, A have high priority than B. B need get the rtnl lock to do something, when B schedule out without release the lock; At this time, the A start to run "echo 1 > /proc/sys/net/ipv6/conf/<ifname>/disable_ipv6", the echo process will run to this code: if (!rtnl_trylock()) return restart_syscall(); Because the rtnl lock was hold by process B, so here the try will be failure, and run the restart_syscall to let the sys_write do again, even try many times, because the B have very lower priority, the lock was hard to be released, so the echo process created by A will enter a loop of restart system call. In my case it is the wireless_nlevent_process in process kworker taken the rtnl lock, and another higher priority process need use echo to disable IPv6 met this problem. I am not very sure, but I think it is better to let the process sleep a while instead of try it again and again without any delay. Expects, what's your opinions? Signed-off-by: Xianpeng Zhao <redacted> --- net/ipv6/addrconf.c | 20 +++++++++++++++----- 1 files changed, 15 insertions(+), 5 deletions(-)
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 38eedde..f06a520 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c@@ -754,8 +754,10 @@ static int addrconf_fixup_forwarding(struct ctl_table *table, int *p, int newf) struct net *net; int old; - if (!rtnl_trylock()) + if (!rtnl_trylock()) { + schedule_timeout_uninterruptible(1); return restart_syscall(); + } net = (struct net *)table->extra2; old = *p;
@@ -811,8 +813,10 @@ static int addrconf_fixup_linkdown(struct ctl_table *table, int *p, int newf) struct net *net; int old; - if (!rtnl_trylock()) + if (!rtnl_trylock()) { + schedule_timeout_uninterruptible(1); return restart_syscall(); + } net = (struct net *)table->extra2; old = *p;
@@ -5304,8 +5308,10 @@ static int addrconf_disable_ipv6(struct ctl_table *table, int *p, int newf) struct net *net; int old; - if (!rtnl_trylock()) + if (!rtnl_trylock()) { + schedule_timeout_uninterruptible(1); return restart_syscall(); + } net = (struct net *)table->extra2; old = *p;
@@ -5367,8 +5373,10 @@ int addrconf_sysctl_proxy_ndp(struct ctl_table *ctl, int write, if (write && old != new) { struct net *net = ctl->extra2; - if (!rtnl_trylock()) + if (!rtnl_trylock()) { + schedule_timeout_uninterruptible(1); return restart_syscall(); + } if (valp == &net->ipv6.devconf_dflt->proxy_ndp) inet6_netconf_notify_devconf(net, NETCONFA_PROXY_NEIGH,
@@ -5408,8 +5416,10 @@ static int addrconf_sysctl_stable_secret(struct ctl_table *ctl, int write, lctl.maxlen = IPV6_MAX_STRLEN; lctl.data = str; - if (!rtnl_trylock()) + if (!rtnl_trylock()) { + schedule_timeout_uninterruptible(1); return restart_syscall(); + } if (!write && !secret->initialized) { err = -EIO;
--
1.7.1