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    Subject[ 67/70] drop_monitor: dont sleep in atomic context
    3.2-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Eric Dumazet <edumazet@google.com>

    commit bec4596b4e6770c7037f21f6bd27567b152dc0d6 upstream.

    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: Ben Hutchings <ben@decadent.org.uk>
    ---
    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)
    @@ -164,22 +135,17 @@ 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);
    @@ -189,7 +155,8 @@ static void trace_drop_common(struct sk_
    goto out;
    }
    }
    -
    + if (msg->entries == dm_hit_limit)
    + goto out;
    /*
    * We need to create a new entry
    */
    @@ -201,13 +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)
    @@ -405,11 +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);
    }




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