[ 022/187] drop_monitor: dont sleep in atomic context

Greg Kroah-Hartman
2012-07-12T23:48:59Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit bec4596b4e6770c7037f21f6bd27567b152dc0d6 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/drop_monitor.c | 102 +++++++++++++++---------------------------------
1 file changed, 33 insertions(+), 69 deletions(-)

--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -33,9 +33,6 @@
#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
@@ -45,11 +42,10 @@ 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 {
@@ -75,13 +71,13 @@ 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);
@@ -96,65 +92,40 @@ static void reset_per_cpu_data(struct pe
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);
+ skb = reset_per_cpu_data(data);

- /*
- * Replace it with a new one
- */
- 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);
+ struct per_cpu_dm_data *data = (struct per_cpu_dm_data *)_data;

- schedule_work_on(smp_processor_id(), &data->dm_alert_work);
-
- put_cpu_var(dm_cpu_data);
+ schedule_work(&data->dm_alert_work);
}

static void trace_drop_common(struct sk_buff *skb, void *location)
@@ -164,33 +135,28 @@ static void trace_drop_common(struct sk_
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
*/
@@ -202,13 +168,11 @@ static void trace_drop_common(struct sk_

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)
@@ -406,11 +370,11 @@ static int __init init_net_drop_monitor(

for_each_present_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);
}