![Neil Horman](/assets/img/avatar_default.png)
I just noticed after some recent updates, that the init path for the drop monitor protocol has a minor error. drop monitor maintains a per cpu structure, that gets initalized from a single cpu. Normally this is fine, as the protocol isn't in use yet, but I recently made a change that causes a failed skb allocation to reschedule itself . Given the current code, the implication is that this workqueue reschedule will take place on the wrong cpu. If drop monitor is used early during the boot process, its possible that two cpus will access a single per-cpu structure in parallel, possibly leading to data corruption. This patch fixes the situation, by storing the cpu number that a given instance of this per-cpu data should be accessed from. In the case of a need for a reschedule, the cpu stored in the struct is assigned the rescheule, rather than the currently executing cpu Tested successfully by myself. Signed-off-by: Neil Horman <nhorman@tuxdriver.com> CC: David Miller <davem@davemloft.net> Signed-off-by: David S. Miller <davem@davemloft.net>
427 lines
9.4 KiB
C
427 lines
9.4 KiB
C
/*
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* Monitoring code for network dropped packet alerts
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*
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* Copyright (C) 2009 Neil Horman <nhorman@tuxdriver.com>
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*/
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#include <linux/netdevice.h>
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#include <linux/etherdevice.h>
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#include <linux/string.h>
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#include <linux/if_arp.h>
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#include <linux/inetdevice.h>
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#include <linux/inet.h>
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#include <linux/interrupt.h>
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#include <linux/netpoll.h>
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#include <linux/sched.h>
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#include <linux/delay.h>
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#include <linux/types.h>
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#include <linux/workqueue.h>
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#include <linux/netlink.h>
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#include <linux/net_dropmon.h>
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#include <linux/percpu.h>
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#include <linux/timer.h>
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#include <linux/bitops.h>
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#include <linux/slab.h>
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#include <net/genetlink.h>
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#include <net/netevent.h>
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#include <trace/events/skb.h>
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#include <trace/events/napi.h>
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#include <asm/unaligned.h>
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#define TRACE_ON 1
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#define TRACE_OFF 0
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static void send_dm_alert(struct work_struct *unused);
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/*
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* Globals, our netlink socket pointer
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* and the work handle that will send up
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* netlink alerts
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*/
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static int trace_state = TRACE_OFF;
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static DEFINE_MUTEX(trace_state_mutex);
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struct per_cpu_dm_data {
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struct work_struct dm_alert_work;
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struct sk_buff __rcu *skb;
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atomic_t dm_hit_count;
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struct timer_list send_timer;
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int cpu;
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};
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struct dm_hw_stat_delta {
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struct net_device *dev;
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unsigned long last_rx;
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struct list_head list;
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struct rcu_head rcu;
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unsigned long last_drop_val;
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};
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static struct genl_family net_drop_monitor_family = {
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.id = GENL_ID_GENERATE,
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.hdrsize = 0,
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.name = "NET_DM",
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.version = 2,
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.maxattr = NET_DM_CMD_MAX,
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};
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static DEFINE_PER_CPU(struct per_cpu_dm_data, dm_cpu_data);
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static int dm_hit_limit = 64;
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static int dm_delay = 1;
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static unsigned long dm_hw_check_delta = 2*HZ;
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static LIST_HEAD(hw_stats_list);
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static void reset_per_cpu_data(struct per_cpu_dm_data *data)
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{
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size_t al;
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struct net_dm_alert_msg *msg;
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struct nlattr *nla;
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struct sk_buff *skb;
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struct sk_buff *oskb = rcu_dereference_protected(data->skb, 1);
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al = sizeof(struct net_dm_alert_msg);
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al += dm_hit_limit * sizeof(struct net_dm_drop_point);
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al += sizeof(struct nlattr);
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skb = genlmsg_new(al, GFP_KERNEL);
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if (skb) {
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genlmsg_put(skb, 0, 0, &net_drop_monitor_family,
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0, NET_DM_CMD_ALERT);
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nla = nla_reserve(skb, NLA_UNSPEC,
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sizeof(struct net_dm_alert_msg));
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msg = nla_data(nla);
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memset(msg, 0, al);
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} else
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schedule_work_on(data->cpu, &data->dm_alert_work);
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/*
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* Don't need to lock this, since we are guaranteed to only
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* run this on a single cpu at a time.
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* Note also that we only update data->skb if the old and new skb
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* pointers don't match. This ensures that we don't continually call
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* synchornize_rcu if we repeatedly fail to alloc a new netlink message.
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*/
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if (skb != oskb) {
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rcu_assign_pointer(data->skb, skb);
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synchronize_rcu();
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atomic_set(&data->dm_hit_count, dm_hit_limit);
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}
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}
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static void send_dm_alert(struct work_struct *unused)
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{
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struct sk_buff *skb;
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struct per_cpu_dm_data *data = &get_cpu_var(dm_cpu_data);
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WARN_ON_ONCE(data->cpu != smp_processor_id());
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/*
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* Grab the skb we're about to send
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*/
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skb = rcu_dereference_protected(data->skb, 1);
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/*
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* Replace it with a new one
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*/
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reset_per_cpu_data(data);
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/*
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* Ship it!
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*/
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if (skb)
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genlmsg_multicast(skb, 0, NET_DM_GRP_ALERT, GFP_KERNEL);
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put_cpu_var(dm_cpu_data);
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}
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/*
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* This is the timer function to delay the sending of an alert
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* in the event that more drops will arrive during the
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* hysteresis period. Note that it operates under the timer interrupt
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* so we don't need to disable preemption here
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*/
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static void sched_send_work(unsigned long unused)
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{
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struct per_cpu_dm_data *data = &get_cpu_var(dm_cpu_data);
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schedule_work_on(smp_processor_id(), &data->dm_alert_work);
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put_cpu_var(dm_cpu_data);
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}
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static void trace_drop_common(struct sk_buff *skb, void *location)
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{
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struct net_dm_alert_msg *msg;
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struct nlmsghdr *nlh;
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struct nlattr *nla;
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int i;
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struct sk_buff *dskb;
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struct per_cpu_dm_data *data = &get_cpu_var(dm_cpu_data);
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rcu_read_lock();
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dskb = rcu_dereference(data->skb);
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if (!dskb)
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goto out;
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if (!atomic_add_unless(&data->dm_hit_count, -1, 0)) {
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/*
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* we're already at zero, discard this hit
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*/
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goto out;
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}
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nlh = (struct nlmsghdr *)dskb->data;
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nla = genlmsg_data(nlmsg_data(nlh));
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msg = nla_data(nla);
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for (i = 0; i < msg->entries; i++) {
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if (!memcmp(&location, msg->points[i].pc, sizeof(void *))) {
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msg->points[i].count++;
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atomic_inc(&data->dm_hit_count);
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goto out;
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}
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}
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/*
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* We need to create a new entry
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*/
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__nla_reserve_nohdr(dskb, sizeof(struct net_dm_drop_point));
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nla->nla_len += NLA_ALIGN(sizeof(struct net_dm_drop_point));
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memcpy(msg->points[msg->entries].pc, &location, sizeof(void *));
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msg->points[msg->entries].count = 1;
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msg->entries++;
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if (!timer_pending(&data->send_timer)) {
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data->send_timer.expires = jiffies + dm_delay * HZ;
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add_timer_on(&data->send_timer, smp_processor_id());
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}
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out:
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rcu_read_unlock();
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put_cpu_var(dm_cpu_data);
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return;
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}
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static void trace_kfree_skb_hit(void *ignore, struct sk_buff *skb, void *location)
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{
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trace_drop_common(skb, location);
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}
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static void trace_napi_poll_hit(void *ignore, struct napi_struct *napi)
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{
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struct dm_hw_stat_delta *new_stat;
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/*
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* Don't check napi structures with no associated device
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*/
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if (!napi->dev)
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return;
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rcu_read_lock();
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list_for_each_entry_rcu(new_stat, &hw_stats_list, list) {
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/*
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* only add a note to our monitor buffer if:
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* 1) this is the dev we received on
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* 2) its after the last_rx delta
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* 3) our rx_dropped count has gone up
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*/
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if ((new_stat->dev == napi->dev) &&
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(time_after(jiffies, new_stat->last_rx + dm_hw_check_delta)) &&
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(napi->dev->stats.rx_dropped != new_stat->last_drop_val)) {
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trace_drop_common(NULL, NULL);
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new_stat->last_drop_val = napi->dev->stats.rx_dropped;
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new_stat->last_rx = jiffies;
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break;
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}
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}
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rcu_read_unlock();
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}
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static int set_all_monitor_traces(int state)
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{
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int rc = 0;
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struct dm_hw_stat_delta *new_stat = NULL;
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struct dm_hw_stat_delta *temp;
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mutex_lock(&trace_state_mutex);
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if (state == trace_state) {
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rc = -EAGAIN;
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goto out_unlock;
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}
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switch (state) {
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case TRACE_ON:
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rc |= register_trace_kfree_skb(trace_kfree_skb_hit, NULL);
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rc |= register_trace_napi_poll(trace_napi_poll_hit, NULL);
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break;
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case TRACE_OFF:
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rc |= unregister_trace_kfree_skb(trace_kfree_skb_hit, NULL);
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rc |= unregister_trace_napi_poll(trace_napi_poll_hit, NULL);
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tracepoint_synchronize_unregister();
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/*
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* Clean the device list
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*/
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list_for_each_entry_safe(new_stat, temp, &hw_stats_list, list) {
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if (new_stat->dev == NULL) {
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list_del_rcu(&new_stat->list);
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kfree_rcu(new_stat, rcu);
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}
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}
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break;
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default:
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rc = 1;
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break;
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}
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if (!rc)
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trace_state = state;
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else
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rc = -EINPROGRESS;
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out_unlock:
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mutex_unlock(&trace_state_mutex);
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return rc;
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}
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static int net_dm_cmd_config(struct sk_buff *skb,
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struct genl_info *info)
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{
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return -ENOTSUPP;
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}
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static int net_dm_cmd_trace(struct sk_buff *skb,
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struct genl_info *info)
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{
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switch (info->genlhdr->cmd) {
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case NET_DM_CMD_START:
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return set_all_monitor_traces(TRACE_ON);
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break;
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case NET_DM_CMD_STOP:
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return set_all_monitor_traces(TRACE_OFF);
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break;
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}
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return -ENOTSUPP;
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}
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static int dropmon_net_event(struct notifier_block *ev_block,
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unsigned long event, void *ptr)
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{
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struct net_device *dev = ptr;
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struct dm_hw_stat_delta *new_stat = NULL;
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struct dm_hw_stat_delta *tmp;
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switch (event) {
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case NETDEV_REGISTER:
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new_stat = kzalloc(sizeof(struct dm_hw_stat_delta), GFP_KERNEL);
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if (!new_stat)
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goto out;
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new_stat->dev = dev;
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new_stat->last_rx = jiffies;
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mutex_lock(&trace_state_mutex);
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list_add_rcu(&new_stat->list, &hw_stats_list);
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mutex_unlock(&trace_state_mutex);
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break;
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case NETDEV_UNREGISTER:
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mutex_lock(&trace_state_mutex);
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list_for_each_entry_safe(new_stat, tmp, &hw_stats_list, list) {
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if (new_stat->dev == dev) {
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new_stat->dev = NULL;
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if (trace_state == TRACE_OFF) {
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list_del_rcu(&new_stat->list);
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kfree_rcu(new_stat, rcu);
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break;
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}
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}
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}
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mutex_unlock(&trace_state_mutex);
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break;
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}
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out:
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return NOTIFY_DONE;
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}
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static struct genl_ops dropmon_ops[] = {
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{
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.cmd = NET_DM_CMD_CONFIG,
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.doit = net_dm_cmd_config,
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},
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{
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.cmd = NET_DM_CMD_START,
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.doit = net_dm_cmd_trace,
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},
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{
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.cmd = NET_DM_CMD_STOP,
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.doit = net_dm_cmd_trace,
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},
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};
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static struct notifier_block dropmon_net_notifier = {
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.notifier_call = dropmon_net_event
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};
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static int __init init_net_drop_monitor(void)
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{
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struct per_cpu_dm_data *data;
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int cpu, rc;
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printk(KERN_INFO "Initializing network drop monitor service\n");
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if (sizeof(void *) > 8) {
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printk(KERN_ERR "Unable to store program counters on this arch, Drop monitor failed\n");
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return -ENOSPC;
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}
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rc = genl_register_family_with_ops(&net_drop_monitor_family,
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dropmon_ops,
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ARRAY_SIZE(dropmon_ops));
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if (rc) {
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printk(KERN_ERR "Could not create drop monitor netlink family\n");
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return rc;
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}
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rc = register_netdevice_notifier(&dropmon_net_notifier);
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if (rc < 0) {
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printk(KERN_CRIT "Failed to register netdevice notifier\n");
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goto out_unreg;
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}
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rc = 0;
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for_each_present_cpu(cpu) {
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data = &per_cpu(dm_cpu_data, cpu);
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data->cpu = cpu;
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INIT_WORK(&data->dm_alert_work, send_dm_alert);
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init_timer(&data->send_timer);
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data->send_timer.data = cpu;
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data->send_timer.function = sched_send_work;
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reset_per_cpu_data(data);
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}
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goto out;
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out_unreg:
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genl_unregister_family(&net_drop_monitor_family);
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out:
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return rc;
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}
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late_initcall(init_net_drop_monitor);
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