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Date: Sun, 1 Apr 2012 12:14:52 -0700
From: Stephen Hemminger <shemminger@...tta.com>
To: bugzilla-daemon@...zilla.kernel.org
Cc: netdev@...r.kernel.org
Subject: Re: [Bug 43018] New: calling function of "dev_queue_xmit()" from a
interrupt may be deadlock.
Redirecting this to netdev list.
I don't think this bug is possible in normal flow because of the implicit
rules about network devices:
The network standard output path is never called with interrupts
disabled. It is called with soft interrupt disabled (ie when forwarding).
Where in the standard kernel code do you see a possibility of calling
dev_queue_xmit with from an interrupt?
There is one special case which is the netconsole/netpoll code which
calls the network device transmit directly (ndo_start_xmit). This code
takes special precautions to allow being called from an interrupt routine
and does not go through dev_queue_xmit().
On Sat, 31 Mar 2012 02:10:51 GMT
bugzilla-daemon@...zilla.kernel.org wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=43018
>
> Summary: calling function of "dev_queue_xmit()" from a
> interrupt may be deadlock.
> Product: Networking
> Version: 2.5
> Kernel Version: 3.0.26
> Platform: All
> OS/Version: Linux
> Tree: Mainline
> Status: NEW
> Severity: normal
> Priority: P1
> Component: IPV4
> AssignedTo: shemminger@...ux-foundation.org
> ReportedBy: qiuli.wu@...bio.com
> Regression: No
>
>
> Enter this function to send packet:
>
> static void net_tx_action(struct softirq_action *h)
> {
> struct softnet_data *sd = &__get_cpu_var(softnet_data);
>
> if (sd->completion_queue) {
> struct sk_buff *clist;
>
> local_irq_disable();
> clist = sd->completion_queue;
> sd->completion_queue = NULL;
> local_irq_enable();
>
> while (clist) {
> struct sk_buff *skb = clist;
> clist = clist->next;
>
> WARN_ON(atomic_read(&skb->users));
> trace_kfree_skb(skb, net_tx_action);
> __kfree_skb(skb);
> }
> }
>
> if (sd->output_queue) {
> struct Qdisc *head;
>
> local_irq_disable();
> head = sd->output_queue;
> sd->output_queue = NULL;
> sd->output_queue_tailp = &sd->output_queue;
> local_irq_enable();
>
> while (head) {
> struct Qdisc *q = head;
> spinlock_t *root_lock;
>
> head = head->next_sched;
>
> root_lock = qdisc_lock(q);
> if (spin_trylock(root_lock)) {
> //##########################################################################
> //here we have got lock of "root_lock",
> //just this time a interrupt coming ,and
> //in this interrupt I call "dev_queue_xmit" to
> //send skb and the Qdisc is same one.
> //############################################################################
> smp_mb__before_clear_bit();
> clear_bit(__QDISC_STATE_SCHED,
> &q->state);
> qdisc_run(q);
> spin_unlock(root_lock);
> } else {
> if (!test_bit(__QDISC_STATE_DEACTIVATED,
> &q->state)) {
> __netif_reschedule(q);
> } else {
> smp_mb__before_clear_bit();
> clear_bit(__QDISC_STATE_SCHED,
> &q->state);
> }
> }
> }
> }
> }
>
>
> //int dev_queue_xmit(struct sk_buff *skb)->__dev_xmit_skb
>
> static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
> struct net_device *dev,
> struct netdev_queue *txq)
> {
> spinlock_t *root_lock = qdisc_lock(q);
> bool contended;
> int rc;
>
> qdisc_skb_cb(skb)->pkt_len = skb->len;
> qdisc_calculate_pkt_len(skb, q);
> /*
> * Heuristic to force contended enqueues to serialize on a
> * separate lock before trying to get qdisc main lock.
> * This permits __QDISC_STATE_RUNNING owner to get the lock more often
> * and dequeue packets faster.
> */
> contended = qdisc_is_running(q);
> if (unlikely(contended))
> spin_lock(&q->busylock);
> //############################################################################
> //HERE can't get root_lock,because soft interrupt have got it and it be
> // interrupted .deadlock happen.
> //#############################################################################
> spin_lock(root_lock);
> if (unlikely(test_bit(__QDISC_STATE_DEACTIVATED, &q->state))) {
> kfree_skb(skb);
> rc = NET_XMIT_DROP;
> } else if ((q->flags & TCQ_F_CAN_BYPASS) && !qdisc_qlen(q) &&
> qdisc_run_begin(q)) {
> /*
> * This is a work-conserving queue; there are no old skbs
> * waiting to be sent out; and the qdisc is not running -
> * xmit the skb directly.
> */
> if (!(dev->priv_flags & IFF_XMIT_DST_RELEASE))
> skb_dst_force(skb);
>
> qdisc_bstats_update(q, skb);
>
> if (sch_direct_xmit(skb, q, dev, txq, root_lock)) {
> if (unlikely(contended)) {
> spin_unlock(&q->busylock);
> contended = false;
> }
> __qdisc_run(q);
> } else
> qdisc_run_end(q);
>
> rc = NET_XMIT_SUCCESS;
> } else {
> skb_dst_force(skb);
> rc = q->enqueue(skb, q) & NET_XMIT_MASK;
> if (qdisc_run_begin(q)) {
> if (unlikely(contended)) {
> spin_unlock(&q->busylock);
> contended = false;
> }
> __qdisc_run(q);
> }
> }
> spin_unlock(root_lock);
> if (unlikely(contended))
> spin_unlock(&q->busylock);
> return rc;
> }
>
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