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    Subject[PATCH AUTOSEL for 4.9 21/33] bpf: fix lockdep splat
    Date
    From: Eric Dumazet <edumazet@google.com>

    [ Upstream commit 89ad2fa3f043a1e8daae193bcb5fe34d5f8caf28 ]

    pcpu_freelist_pop() needs the same lockdep awareness than
    pcpu_freelist_populate() to avoid a false positive.

    [ INFO: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected ]

    switchto-defaul/12508 [HC0[0]:SC0[6]:HE0:SE0] is trying to acquire:
    (&htab->buckets[i].lock){......}, at: [<ffffffff9dc099cb>] __htab_percpu_map_update_elem+0x1cb/0x300

    and this task is already holding:
    (dev_queue->dev->qdisc_class ?: &qdisc_tx_lock#2){+.-...}, at: [<ffffffff9e135848>] __dev_queue_xmit+0
    x868/0x1240
    which would create a new lock dependency:
    (dev_queue->dev->qdisc_class ?: &qdisc_tx_lock#2){+.-...} -> (&htab->buckets[i].lock){......}

    but this new dependency connects a SOFTIRQ-irq-safe lock:
    (dev_queue->dev->qdisc_class ?: &qdisc_tx_lock#2){+.-...}
    ... which became SOFTIRQ-irq-safe at:
    [<ffffffff9db5931b>] __lock_acquire+0x42b/0x1f10
    [<ffffffff9db5b32c>] lock_acquire+0xbc/0x1b0
    [<ffffffff9da05e38>] _raw_spin_lock+0x38/0x50
    [<ffffffff9e135848>] __dev_queue_xmit+0x868/0x1240
    [<ffffffff9e136240>] dev_queue_xmit+0x10/0x20
    [<ffffffff9e1965d9>] ip_finish_output2+0x439/0x590
    [<ffffffff9e197410>] ip_finish_output+0x150/0x2f0
    [<ffffffff9e19886d>] ip_output+0x7d/0x260
    [<ffffffff9e19789e>] ip_local_out+0x5e/0xe0
    [<ffffffff9e197b25>] ip_queue_xmit+0x205/0x620
    [<ffffffff9e1b8398>] tcp_transmit_skb+0x5a8/0xcb0
    [<ffffffff9e1ba152>] tcp_write_xmit+0x242/0x1070
    [<ffffffff9e1baffc>] __tcp_push_pending_frames+0x3c/0xf0
    [<ffffffff9e1b3472>] tcp_rcv_established+0x312/0x700
    [<ffffffff9e1c1acc>] tcp_v4_do_rcv+0x11c/0x200
    [<ffffffff9e1c3dc2>] tcp_v4_rcv+0xaa2/0xc30
    [<ffffffff9e191107>] ip_local_deliver_finish+0xa7/0x240
    [<ffffffff9e191a36>] ip_local_deliver+0x66/0x200
    [<ffffffff9e19137d>] ip_rcv_finish+0xdd/0x560
    [<ffffffff9e191e65>] ip_rcv+0x295/0x510
    [<ffffffff9e12ff88>] __netif_receive_skb_core+0x988/0x1020
    [<ffffffff9e130641>] __netif_receive_skb+0x21/0x70
    [<ffffffff9e1306ff>] process_backlog+0x6f/0x230
    [<ffffffff9e132129>] net_rx_action+0x229/0x420
    [<ffffffff9da07ee8>] __do_softirq+0xd8/0x43d
    [<ffffffff9e282bcc>] do_softirq_own_stack+0x1c/0x30
    [<ffffffff9dafc2f5>] do_softirq+0x55/0x60
    [<ffffffff9dafc3a8>] __local_bh_enable_ip+0xa8/0xb0
    [<ffffffff9db4c727>] cpu_startup_entry+0x1c7/0x500
    [<ffffffff9daab333>] start_secondary+0x113/0x140

    to a SOFTIRQ-irq-unsafe lock:
    (&head->lock){+.+...}
    ... which became SOFTIRQ-irq-unsafe at:
    ... [<ffffffff9db5971f>] __lock_acquire+0x82f/0x1f10
    [<ffffffff9db5b32c>] lock_acquire+0xbc/0x1b0
    [<ffffffff9da05e38>] _raw_spin_lock+0x38/0x50
    [<ffffffff9dc0b7fa>] pcpu_freelist_pop+0x7a/0xb0
    [<ffffffff9dc08b2c>] htab_map_alloc+0x50c/0x5f0
    [<ffffffff9dc00dc5>] SyS_bpf+0x265/0x1200
    [<ffffffff9e28195f>] entry_SYSCALL_64_fastpath+0x12/0x17

    other info that might help us debug this:

    Chain exists of:
    dev_queue->dev->qdisc_class ?: &qdisc_tx_lock#2 --> &htab->buckets[i].lock --> &head->lock

    Possible interrupt unsafe locking scenario:

    CPU0 CPU1
    ---- ----
    lock(&head->lock);
    local_irq_disable();
    lock(dev_queue->dev->qdisc_class ?: &qdisc_tx_lock#2);
    lock(&htab->buckets[i].lock);
    <Interrupt>
    lock(dev_queue->dev->qdisc_class ?: &qdisc_tx_lock#2);

    *** DEADLOCK ***

    Fixes: e19494edab82 ("bpf: introduce percpu_freelist")
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
    ---
    kernel/bpf/percpu_freelist.c | 8 ++++++--
    1 file changed, 6 insertions(+), 2 deletions(-)

    diff --git a/kernel/bpf/percpu_freelist.c b/kernel/bpf/percpu_freelist.c
    index 5c51d1985b51..673fa6fe2d73 100644
    --- a/kernel/bpf/percpu_freelist.c
    +++ b/kernel/bpf/percpu_freelist.c
    @@ -78,8 +78,10 @@ struct pcpu_freelist_node *pcpu_freelist_pop(struct pcpu_freelist *s)
    {
    struct pcpu_freelist_head *head;
    struct pcpu_freelist_node *node;
    + unsigned long flags;
    int orig_cpu, cpu;

    + local_irq_save(flags);
    orig_cpu = cpu = raw_smp_processor_id();
    while (1) {
    head = per_cpu_ptr(s->freelist, cpu);
    @@ -87,14 +89,16 @@ struct pcpu_freelist_node *pcpu_freelist_pop(struct pcpu_freelist *s)
    node = head->first;
    if (node) {
    head->first = node->next;
    - raw_spin_unlock(&head->lock);
    + raw_spin_unlock_irqrestore(&head->lock, flags);
    return node;
    }
    raw_spin_unlock(&head->lock);
    cpu = cpumask_next(cpu, cpu_possible_mask);
    if (cpu >= nr_cpu_ids)
    cpu = 0;
    - if (cpu == orig_cpu)
    + if (cpu == orig_cpu) {
    + local_irq_restore(flags);
    return NULL;
    + }
    }
    }
    --
    2.11.0
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