Re: [PATCH] ath9k: Fix possible stall on ath9k_txq_list_has_key()

["Nicolas Escande" <nico.escande@gmail.com>]

On Fri Jun 9, 2023 at 11:37 AM CEST, Remi Pommarel wrote:
> On EDMA capable hardware, ath9k_txq_list_has_key() can enter infinite
> loop if it is called while all txq_fifos have packets that use different
> key that the one we are looking for. Fix it by exiting the loop if all
> txq_fifos have been checked already.
>
> Because this loop is called under spin_lock_bh() (see ath_txq_lock) it
> causes the following rcu stall:
>
> rcu: INFO: rcu_sched self-detected stall on CPU
> ath10k_pci 0000:01:00.0: failed to read temperature -11
> rcu:    1-....: (5254 ticks this GP) idle=189/1/0x4000000000000002 softirq=8442983/8442984 fqs=2579
>         (t=5257 jiffies g=17983297 q=334)
> Task dump for CPU 1:
> task:hostapd         state:R  running task     stack:    0 pid:  297 ppid:   289 flags:0x0000000a
> Call trace:
>  dump_backtrace+0x0/0x170
>  show_stack+0x1c/0x24
>  sched_show_task+0x140/0x170
>  dump_cpu_task+0x48/0x54
>  rcu_dump_cpu_stacks+0xf0/0x134
>  rcu_sched_clock_irq+0x8d8/0x9fc
>  update_process_times+0xa0/0xec
>  tick_sched_timer+0x5c/0xd0
>  __hrtimer_run_queues+0x154/0x320
>  hrtimer_interrupt+0x120/0x2f0
>  arch_timer_handler_virt+0x38/0x44
>  handle_percpu_devid_irq+0x9c/0x1e0
>  handle_domain_irq+0x64/0x90
>  gic_handle_irq+0x78/0xb0
>  call_on_irq_stack+0x28/0x38
>  do_interrupt_handler+0x54/0x5c
>  el1_interrupt+0x2c/0x4c
>  el1h_64_irq_handler+0x14/0x1c
>  el1h_64_irq+0x74/0x78
>  ath9k_txq_has_key+0x1bc/0x250 [ath9k]
>  ath9k_set_key+0x1cc/0x3dc [ath9k]
>  drv_set_key+0x78/0x170
>  ieee80211_key_replace+0x564/0x6cc
>  ieee80211_key_link+0x174/0x220
>  ieee80211_add_key+0x11c/0x300
>  nl80211_new_key+0x12c/0x330
>  genl_family_rcv_msg_doit+0xbc/0x11c
>  genl_rcv_msg+0xd8/0x1c4
>  netlink_rcv_skb+0x40/0x100
>  genl_rcv+0x3c/0x50
>  netlink_unicast+0x1ec/0x2c0
>  netlink_sendmsg+0x198/0x3c0
>  ____sys_sendmsg+0x210/0x250
>  ___sys_sendmsg+0x78/0xc4
>  __sys_sendmsg+0x4c/0x90
>  __arm64_sys_sendmsg+0x28/0x30
>  invoke_syscall.constprop.0+0x60/0x100
>  do_el0_svc+0x48/0xd0
>  el0_svc+0x14/0x50
>  el0t_64_sync_handler+0xa8/0xb0
>  el0t_64_sync+0x158/0x15c
>
> This rcu stall is hard to reproduce as is, but changing ATH_TXFIFO_DEPTH
> from 8 to 2 makes it reasonably easy to reproduce.
>
> Fixes: ca2848022c12 ("ath9k: Postpone key cache entry deletion for TXQ frames reference it")
> Signed-off-by: Remi Pommarel <repk@triplefau.lt>
> ---
>  drivers/net/wireless/ath/ath9k/main.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/wireless/ath/ath9k/main.c b/drivers/net/wireless/ath/ath9k/main.c
> index a4197c14f0a9..7f9f06ea8a05 100644
> --- a/drivers/net/wireless/ath/ath9k/main.c
> +++ b/drivers/net/wireless/ath/ath9k/main.c
> @@ -850,7 +850,7 @@ static bool ath9k_txq_list_has_key(struct list_head *txq_list, u32 keyix)
>  static bool ath9k_txq_has_key(struct ath_softc *sc, u32 keyix)
>  {
>  	struct ath_hw *ah = sc->sc_ah;
> -	int i;
> +	int i, j;
>  	struct ath_txq *txq;
>  	bool key_in_use = false;
>  
> @@ -868,8 +868,9 @@ static bool ath9k_txq_has_key(struct ath_softc *sc, u32 keyix)
>  		if (sc->sc_ah->caps.hw_caps & ATH9K_HW_CAP_EDMA) {
>  			int idx = txq->txq_tailidx;
>  
> -			while (!key_in_use &&
> -			       !list_empty(&txq->txq_fifo[idx])) {
> +			for (j = 0; !key_in_use &&
> +			     !list_empty(&txq->txq_fifo[idx]) &&
> +			     j < ATH_TXFIFO_DEPTH; j++) {
>  				key_in_use = ath9k_txq_list_has_key(
>  					&txq->txq_fifo[idx], keyix);
>  				INCR(idx, ATH_TXFIFO_DEPTH);

Works with AR9392 (Qualcomm Atheros AR93xx Wireless Network Adapter (rev 01))

Tested-by: Nicolas Escande <nico.escande@gmail.com>

---
Nicolas E.