Re: [PATCH v6.1] wifi: ath11k: avoid deadlock during regulatory update in ath11k_regd_update()

[Kalle Valo <kvalo@kernel.org>]

Kalle Valo <kvalo@kernel.org> writes:

> From: Wen Gong <quic_wgong@quicinc.com>
>
> (cherry picked from commit d99884ad9e3673a12879bc2830f6e5a66cccbd78 in ath-next
> as users are seeing this bug more now, also cc stable)
>
> Running this test in a loop it is easy to reproduce an rtnl deadlock:
>
> iw reg set FI
> ifconfig wlan0 down
>
> What happens is that thread A (workqueue) tries to update the regulatory:
>
>     try to acquire the rtnl_lock of ar->regd_update_work
>
>     rtnl_lock+0x17/0x20
>     ath11k_regd_update+0x15a/0x260 [ath11k]
>     ath11k_regd_update_work+0x15/0x20 [ath11k]
>     process_one_work+0x228/0x670
>     worker_thread+0x4d/0x440
>     kthread+0x16d/0x1b0
>     ret_from_fork+0x22/0x30
>
> And thread B (ifconfig) tries to stop the interface:
>
>     try to cancel_work_sync(&ar->regd_update_work) in ath11k_mac_op_stop().
>     ifconfig  3109 [003]  2414.232506: probe:
>
>     ath11k_mac_op_stop: (ffffffffc14187a0)
>     drv_stop+0x30 ([mac80211])
>     ieee80211_do_stop+0x5d2 ([mac80211])
>     ieee80211_stop+0x3e ([mac80211])
>     __dev_close_many+0x9e ([kernel.kallsyms])
>     __dev_change_flags+0xbe ([kernel.kallsyms])
>     dev_change_flags+0x23 ([kernel.kallsyms])
>     devinet_ioctl+0x5e3 ([kernel.kallsyms])
>     inet_ioctl+0x197 ([kernel.kallsyms])
>     sock_do_ioctl+0x4d ([kernel.kallsyms])
>     sock_ioctl+0x264 ([kernel.kallsyms])
>     __x64_sys_ioctl+0x92 ([kernel.kallsyms])
>     do_syscall_64+0x3a ([kernel.kallsyms])
>     entry_SYSCALL_64_after_hwframe+0x63 ([kernel.kallsyms])
>     __GI___ioctl+0x7 (/lib/x86_64-linux-gnu/libc-2.23.so)
>
> The sequence of deadlock is:
>
> 1. Thread B calls rtnl_lock().
>
> 2. Thread A starts to run and calls rtnl_lock() from within
>    ath11k_regd_update_work(), then enters wait state because the lock is owned by
>    thread B.
>
> 3. Thread B continues to run and tries to call
>    cancel_work_sync(&ar->regd_update_work), but thread A is in
>    ath11k_regd_update_work() waiting for rtnl_lock(). So cancel_work_sync()
>    forever waits for ath11k_regd_update_work() to finish and we have a deadlock.
>
> Fix this by switching from using regulatory_set_wiphy_regd_sync() to
> regulatory_set_wiphy_regd(). Now cfg80211 will schedule another workqueue which
> handles the locking on it's own. So the ath11k workqueue can simply exit without
> taking any locks, avoiding the deadlock.
>
> Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3
>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Wen Gong <quic_wgong@quicinc.com>
> [kvalo: improve commit log]
> Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>

Manually applied to ath-current branch of ath.git.

f45cb6b29cd3 wifi: ath11k: avoid deadlock during regulatory update in ath11k_regd_update()

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