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drop_monitor: dont sleep in atomic context
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drop_monitor calls several sleeping functions while in atomic context.

 BUG: sleeping function called from invalid context at mm/slub.c:943
 in_atomic(): 1, irqs_disabled(): 0, pid: 2103, name: kworker/0:2
 Pid: 2103, comm: kworker/0:2 Not tainted 3.5.0-rc1+ #55
 Call Trace:
  [<ffffffff810697ca>] __might_sleep+0xca/0xf0
  [<ffffffff811345a3>] kmem_cache_alloc_node+0x1b3/0x1c0
  [<ffffffff8105578c>] ? queue_delayed_work_on+0x11c/0x130
  [<ffffffff815343fb>] __alloc_skb+0x4b/0x230
  [<ffffffffa00b0360>] ? reset_per_cpu_data+0x160/0x160 [drop_monitor]
  [<ffffffffa00b022f>] reset_per_cpu_data+0x2f/0x160 [drop_monitor]
  [<ffffffffa00b03ab>] send_dm_alert+0x4b/0xb0 [drop_monitor]
  [<ffffffff810568e0>] process_one_work+0x130/0x4c0
  [<ffffffff81058249>] worker_thread+0x159/0x360
  [<ffffffff810580f0>] ? manage_workers.isra.27+0x240/0x240
  [<ffffffff8105d403>] kthread+0x93/0xa0
  [<ffffffff816be6d4>] kernel_thread_helper+0x4/0x10
  [<ffffffff8105d370>] ? kthread_freezable_should_stop+0x80/0x80
  [<ffffffff816be6d0>] ? gs_change+0xb/0xb

Rework the logic to call the sleeping functions in right context.

Use standard timer/workqueue api to let system chose any cpu to perform
the allocation and netlink send.

Also avoid a loop if reset_per_cpu_data() cannot allocate memory :
use mod_timer() to wait 1/10 second before next try.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Neil Horman <nhorman@tuxdriver.com>
Reviewed-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Eric Dumazet authored and David S. Miller committed Jun 4, 2012
1 parent f8f5701 commit bec4596
Showing 1 changed file with 33 additions and 69 deletions.
102 changes: 33 additions & 69 deletions net/core/drop_monitor.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -36,9 +36,6 @@
#define TRACE_ON 1
#define TRACE_OFF 0

static void send_dm_alert(struct work_struct *unused);


/*
* Globals, our netlink socket pointer
* and the work handle that will send up
Expand All @@ -48,11 +45,10 @@ static int trace_state = TRACE_OFF;
static DEFINE_MUTEX(trace_state_mutex);

struct per_cpu_dm_data {
struct work_struct dm_alert_work;
struct sk_buff __rcu *skb;
atomic_t dm_hit_count;
struct timer_list send_timer;
int cpu;
spinlock_t lock;
struct sk_buff *skb;
struct work_struct dm_alert_work;
struct timer_list send_timer;
};

struct dm_hw_stat_delta {
Expand All @@ -78,13 +74,13 @@ static int dm_delay = 1;
static unsigned long dm_hw_check_delta = 2*HZ;
static LIST_HEAD(hw_stats_list);

static void reset_per_cpu_data(struct per_cpu_dm_data *data)
static struct sk_buff *reset_per_cpu_data(struct per_cpu_dm_data *data)
{
size_t al;
struct net_dm_alert_msg *msg;
struct nlattr *nla;
struct sk_buff *skb;
struct sk_buff *oskb = rcu_dereference_protected(data->skb, 1);
unsigned long flags;

al = sizeof(struct net_dm_alert_msg);
al += dm_hit_limit * sizeof(struct net_dm_drop_point);
Expand All @@ -99,65 +95,40 @@ static void reset_per_cpu_data(struct per_cpu_dm_data *data)
sizeof(struct net_dm_alert_msg));
msg = nla_data(nla);
memset(msg, 0, al);
} else
schedule_work_on(data->cpu, &data->dm_alert_work);

/*
* Don't need to lock this, since we are guaranteed to only
* run this on a single cpu at a time.
* Note also that we only update data->skb if the old and new skb
* pointers don't match. This ensures that we don't continually call
* synchornize_rcu if we repeatedly fail to alloc a new netlink message.
*/
if (skb != oskb) {
rcu_assign_pointer(data->skb, skb);

synchronize_rcu();

atomic_set(&data->dm_hit_count, dm_hit_limit);
} else {
mod_timer(&data->send_timer, jiffies + HZ / 10);
}

spin_lock_irqsave(&data->lock, flags);
swap(data->skb, skb);
spin_unlock_irqrestore(&data->lock, flags);

return skb;
}

static void send_dm_alert(struct work_struct *unused)
static void send_dm_alert(struct work_struct *work)
{
struct sk_buff *skb;
struct per_cpu_dm_data *data = &get_cpu_var(dm_cpu_data);
struct per_cpu_dm_data *data;

WARN_ON_ONCE(data->cpu != smp_processor_id());
data = container_of(work, struct per_cpu_dm_data, dm_alert_work);

/*
* Grab the skb we're about to send
*/
skb = rcu_dereference_protected(data->skb, 1);

/*
* Replace it with a new one
*/
reset_per_cpu_data(data);
skb = reset_per_cpu_data(data);

/*
* Ship it!
*/
if (skb)
genlmsg_multicast(skb, 0, NET_DM_GRP_ALERT, GFP_KERNEL);

put_cpu_var(dm_cpu_data);
}

/*
* This is the timer function to delay the sending of an alert
* in the event that more drops will arrive during the
* hysteresis period. Note that it operates under the timer interrupt
* so we don't need to disable preemption here
* hysteresis period.
*/
static void sched_send_work(unsigned long unused)
static void sched_send_work(unsigned long _data)
{
struct per_cpu_dm_data *data = &get_cpu_var(dm_cpu_data);

schedule_work_on(smp_processor_id(), &data->dm_alert_work);
struct per_cpu_dm_data *data = (struct per_cpu_dm_data *)_data;

put_cpu_var(dm_cpu_data);
schedule_work(&data->dm_alert_work);
}

static void trace_drop_common(struct sk_buff *skb, void *location)
Expand All @@ -167,33 +138,28 @@ static void trace_drop_common(struct sk_buff *skb, void *location)
struct nlattr *nla;
int i;
struct sk_buff *dskb;
struct per_cpu_dm_data *data = &get_cpu_var(dm_cpu_data);

struct per_cpu_dm_data *data;
unsigned long flags;

rcu_read_lock();
dskb = rcu_dereference(data->skb);
local_irq_save(flags);
data = &__get_cpu_var(dm_cpu_data);
spin_lock(&data->lock);
dskb = data->skb;

if (!dskb)
goto out;

if (!atomic_add_unless(&data->dm_hit_count, -1, 0)) {
/*
* we're already at zero, discard this hit
*/
goto out;
}

nlh = (struct nlmsghdr *)dskb->data;
nla = genlmsg_data(nlmsg_data(nlh));
msg = nla_data(nla);
for (i = 0; i < msg->entries; i++) {
if (!memcmp(&location, msg->points[i].pc, sizeof(void *))) {
msg->points[i].count++;
atomic_inc(&data->dm_hit_count);
goto out;
}
}

if (msg->entries == dm_hit_limit)
goto out;
/*
* We need to create a new entry
*/
Expand All @@ -205,13 +171,11 @@ static void trace_drop_common(struct sk_buff *skb, void *location)

if (!timer_pending(&data->send_timer)) {
data->send_timer.expires = jiffies + dm_delay * HZ;
add_timer_on(&data->send_timer, smp_processor_id());
add_timer(&data->send_timer);
}

out:
rcu_read_unlock();
put_cpu_var(dm_cpu_data);
return;
spin_unlock_irqrestore(&data->lock, flags);
}

static void trace_kfree_skb_hit(void *ignore, struct sk_buff *skb, void *location)
Expand Down Expand Up @@ -418,11 +382,11 @@ static int __init init_net_drop_monitor(void)

for_each_possible_cpu(cpu) {
data = &per_cpu(dm_cpu_data, cpu);
data->cpu = cpu;
INIT_WORK(&data->dm_alert_work, send_dm_alert);
init_timer(&data->send_timer);
data->send_timer.data = cpu;
data->send_timer.data = (unsigned long)data;
data->send_timer.function = sched_send_work;
spin_lock_init(&data->lock);
reset_per_cpu_data(data);
}

Expand Down

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