wifi: mac80211: fortify the spinlock against deadlock by interrupt

In the Linux kernel, the following vulnerability has been resolved:

wifi: mac80211: fortify the spinlock against deadlock by interrupt

In the function ieee80211_tx_dequeue() there is a particular locking

sequence:

begin:

spin_lock(&local->queue_stop_reason_lock);

q_stopped = local->queue_stop_reasons[q];

spin_unlock(&local->queue_stop_reason_lock);

However small the chance (increased by ftracetest), an asynchronous

interrupt can occur in between of spin_lock() and spin_unlock(),

and the interrupt routine will attempt to lock the same

&local->queue_stop_reason_lock again.

This will cause a costly reset of the CPU and the wifi device or an

altogether hang in the single CPU and single core scenario.

The only remaining spin_lock(&local->queue_stop_reason_lock) that

did not disable interrupts was patched, which should prevent any

deadlocks on the same CPU/core and the same wifi device.

This is the probable trace of the deadlock:

kernel: ================================

kernel: WARNING: inconsistent lock state

kernel: 6.3.0-rc6-mt-20230401-00001-gf86822a1170f #4 Tainted: G W

kernel: --------------------------------

kernel: inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage.

kernel: kworker/5:0/25656 [HC0[0]:SC0[0]:HE1:SE1] takes:

kernel: ffff9d6190779478 (&local->queue_stop_reason_lock){+.?.}-{2:2}, at: return_to_handler+0x0/0x40

kernel: {IN-SOFTIRQ-W} state was registered at:

kernel: lock_acquire+0xc7/0x2d0

kernel: _raw_spin_lock+0x36/0x50

kernel: ieee80211_tx_dequeue+0xb4/0x1330 [mac80211]

kernel: iwl_mvm_mac_itxq_xmit+0xae/0x210 [iwlmvm]

kernel: iwl_mvm_mac_wake_tx_queue+0x2d/0xd0 [iwlmvm]

kernel: ieee80211_queue_skb+0x450/0x730 [mac80211]

kernel: __ieee80211_xmit_fast.constprop.66+0x834/0xa50 [mac80211]

kernel: __ieee80211_subif_start_xmit+0x217/0x530 [mac80211]

kernel: ieee80211_subif_start_xmit+0x60/0x580 [mac80211]

kernel: dev_hard_start_xmit+0xb5/0x260

kernel: __dev_queue_xmit+0xdbe/0x1200

kernel: neigh_resolve_output+0x166/0x260

kernel: ip_finish_output2+0x216/0xb80

kernel: __ip_finish_output+0x2a4/0x4d0

kernel: ip_finish_output+0x2d/0xd0

kernel: ip_output+0x82/0x2b0

kernel: ip_local_out+0xec/0x110

kernel: igmpv3_sendpack+0x5c/0x90

kernel: igmp_ifc_timer_expire+0x26e/0x4e0

kernel: call_timer_fn+0xa5/0x230

kernel: run_timer_softirq+0x27f/0x550

kernel: __do_softirq+0xb4/0x3a4

kernel: irq_exit_rcu+0x9b/0xc0

kernel: sysvec_apic_timer_interrupt+0x80/0xa0

kernel: asm_sysvec_apic_timer_interrupt+0x1f/0x30

kernel: _raw_spin_unlock_irqrestore+0x3f/0x70

kernel: free_to_partial_list+0x3d6/0x590

kernel: __slab_free+0x1b7/0x310

kernel: kmem_cache_free+0x52d/0x550

kernel: putname+0x5d/0x70

kernel: do_sys_openat2+0x1d7/0x310

kernel: do_sys_open+0x51/0x80

kernel: __x64_sys_openat+0x24/0x30

kernel: do_syscall_64+0x5c/0x90

kernel: entry_SYSCALL_64_after_hwframe+0x72/0xdc

kernel: irq event stamp: 5120729

kernel: hardirqs last enabled at (5120729): [<ffffffff9d149936>] trace_graph_return+0xd6/0x120

kernel: hardirqs last disabled at (5120728): [<ffffffff9d149950>] trace_graph_return+0xf0/0x120

kernel: softirqs last enabled at (5069900): [<ffffffff9cf65b60>] return_to_handler+0x0/0x40

kernel: softirqs last disabled at (5067555): [<ffffffff9cf65b60>] return_to_handler+0x0/0x40

kernel:

other info that might help us debug this:

kernel: Possible unsafe locking scenario:

kernel: CPU0

kernel: ----

kernel: lock(&local->queue_stop_reason_lock);

kernel: <Interrupt>

kernel: lock(&local->queue_stop_reason_lock);

kernel:

*** DEADLOCK ***

kernel: 8 locks held by kworker/5:0/25656:

kernel: #0: ffff9d618009d138 ((wq_completion)events_freezable){+.+.}-{0:0}, at: process_one_work+0x1ca/0x530

kernel: #1: ffffb1ef4637fe68 ((work_completion)(&local->restart_work)){+.+.}-{0:0}, at: process_one_work+0x1ce/0x530

kernel: #2: ffffffff9f166548 (rtnl_mutex){+.+.}-{3:3}, at: return_to_handler+0x0/0x40

kernel: #3: ffff9d619

---truncated---