The netconsole driver currently deadlocks if a NETDEV_UNREGISTER event is received while netconsole is in use, which in turn causes it to pin a reference to the network device. The first deadlock was dealt with in 3b410a31 so that we wouldn't recursively grab RTNL, but even calling __netpoll_cleanup isn't safe to do considering that we are in atomic context. __netpoll_cleanup assumes it can sleep and has several sleeping calls, such as synchronize_rcu_bh and cancel_rearming_delayed_work.
Fix this by deferring netpoll_cleanup using scheduling work that operates in process context. We have to grab a reference to the config_item in this case as we need to pin the item in place until it is operated on. Signed-off-by: Mike Waychison <[email protected]> --- drivers/net/netconsole.c | 55 ++++++++++++++++++++++++++++++++++++++++------ 1 files changed, 48 insertions(+), 7 deletions(-) diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c index 288a025..02ba5c4 100644 --- a/drivers/net/netconsole.c +++ b/drivers/net/netconsole.c @@ -106,6 +106,7 @@ struct netconsole_target { #endif int np_state; struct netpoll np; + struct work_struct cleanup_work; }; #ifdef CONFIG_NETCONSOLE_DYNAMIC @@ -166,6 +167,22 @@ static void netconsole_target_put(struct netconsole_target *nt) #endif /* CONFIG_NETCONSOLE_DYNAMIC */ +static void deferred_netpoll_cleanup(struct work_struct *work) +{ + struct netconsole_target *nt; + unsigned long flags; + + nt = container_of(work, struct netconsole_target, cleanup_work); + netpoll_cleanup(&nt->np); + + spin_lock_irqsave(&target_list_lock, flags); + BUG_ON(nt->np_state != NETPOLL_CLEANING); + nt->np_state = NETPOLL_DISABLED; + spin_unlock_irqrestore(&target_list_lock, flags); + + netconsole_target_put(nt); +} + /* Allocate new target (from boot/module param) and setup netpoll for it */ static struct netconsole_target *alloc_param_target(char *target_config) { @@ -187,6 +204,7 @@ static struct netconsole_target *alloc_param_target(char *target_config) nt->np.local_port = 6665; nt->np.remote_port = 6666; memset(nt->np.remote_mac, 0xff, ETH_ALEN); + INIT_WORK(&nt->cleanup_work, deferred_netpoll_cleanup); /* Parse parameters and setup netpoll */ err = netpoll_parse_options(&nt->np, target_config); @@ -209,7 +227,9 @@ fail: /* Cleanup netpoll for given target (from boot/module param) and free it */ static void free_param_target(struct netconsole_target *nt) { - netpoll_cleanup(&nt->np); + cancel_work_sync(&nt->cleanup_work); + if (nt->np_state == NETPOLL_CLEANING || nt->np_state == NETPOLL_ENABLED) + netpoll_cleanup(&nt->np); kfree(nt); } @@ -350,6 +370,13 @@ static ssize_t store_enabled(struct netconsole_target *nt, goto busy; else { nt->np_state = NETPOLL_SETTINGUP; + /* + * Nominally, we would grab an extra reference on the + * config_item here for dynamic targets while we let go + * of the lock, but this isn't required in this case + * because there is a reference implicitly held by the + * caller of the store operation. + */ spin_unlock_irqrestore(&target_list_lock, flags); } @@ -635,6 +662,7 @@ static struct config_item *make_netconsole_target(struct config_group *group, nt->np.local_port = 6665; nt->np.remote_port = 6666; memset(nt->np.remote_mac, 0xff, ETH_ALEN); + INIT_WORK(&nt->cleanup_work, deferred_netpoll_cleanup); /* Initialize the config_item member */ config_item_init_type_name(&nt->item, name, &netconsole_target_type); @@ -660,6 +688,9 @@ static void drop_netconsole_target(struct config_group *group, /* * The target may have never been enabled, or was manually disabled * before being removed so netpoll may have already been cleaned up. + * + * If it queued for cleanup already, that is fine, as that path holds a + * reference to the config_item. */ if (nt->np_state == NETPOLL_ENABLED) netpoll_cleanup(&nt->np); @@ -689,6 +720,19 @@ static struct configfs_subsystem netconsole_subsys = { #endif /* CONFIG_NETCONSOLE_DYNAMIC */ +/* + * Call netpoll_cleanup on this target asynchronously. + * target_list_lock is required. + */ +static void defer_netpoll_cleanup(struct netconsole_target *nt) +{ + if (nt->np_state != NETPOLL_ENABLED) + return; + netconsole_target_get(nt); + nt->np_state = NETPOLL_CLEANING; + schedule_work(&nt->cleanup_work); +} + /* Handle network interface device notifications */ static int netconsole_netdev_event(struct notifier_block *this, unsigned long event, @@ -712,13 +756,10 @@ static int netconsole_netdev_event(struct notifier_block *this, case NETDEV_BONDING_DESLAVE: case NETDEV_UNREGISTER: /* - * rtnl_lock already held + * We can't cleanup netpoll in atomic context. + * Kick it off as deferred work. */ - if (nt->np.dev) { - __netpoll_cleanup(&nt->np); - dev_put(nt->np.dev); - nt->np.dev = NULL; - } + defer_netpoll_cleanup(nt); } } } -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
