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

From: Kalle Valo <kvalo@kernel.org>
To: Kalle Valo <kvalo@kernel.org>
Cc: ath11k@lists.infradead.org, linux-wireless@vger.kernel.org
Subject: Re: [PATCH] wifi: ath11k: avoid deadlock during regulatory update in ath11k_regd_update()
Date: Mon, 10 Oct 2022 09:38:40 +0000 (UTC)	[thread overview]
Message-ID: <166539471639.12656.4045155375066520132.kvalo@kernel.org> (raw)
In-Reply-To: <20221006151747.13757-1-kvalo@kernel.org>

Kalle Valo <kvalo@kernel.org> wrote:

> 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
> 
> Signed-off-by: Wen Gong <quic_wgong@quicinc.com>
> [kvalo: improve commit log]
> Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>

Patch applied to ath-next branch of ath.git, thanks.

d99884ad9e36 wifi: ath11k: avoid deadlock during regulatory update in ath11k_regd_update()

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https://patchwork.kernel.org/project/linux-wireless/patch/20221006151747.13757-1-kvalo@kernel.org/

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