netdev - Re: [RFC] ath11k: fix netdev open race

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Date:   Tue, 24 May 2022 09:26:23 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Kalle Valo <kvalo@...nel.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, ath11k@...ts.infradead.org,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC] ath11k: fix netdev open race

On Mon, May 23, 2022 at 10:06:37PM +0300, Kalle Valo wrote:
> Johan Hovold <johan@...nel.org> writes:
> 
> > On Tue, May 17, 2022 at 12:34:36PM +0200, Johan Hovold wrote:
> >> Make sure to allocate resources needed before registering the device.
> >> 
> >> This specifically avoids having a racing open() trigger a BUG_ON() in
> >> mod_timer() when ath11k_mac_op_start() is called before the
> >> mon_reap_timer as been set up.
> >> 
> >> Fixes: d5c65159f289 ("ath11k: driver for Qualcomm IEEE 802.11ax devices")
> >> Fixes: 840c36fa727a ("ath11k: dp: stop rx pktlog before suspend")
> >> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> >> ---
> >
> > For completeness:
> >
> > Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3
> 
> Thanks, added in the pending branch.
> 
> You submitted this as RFC but do you mind if I apply this anyway? The
> patch looks good and passes my tests. But I do wonder why I haven't seen
> the crash...

If it looks good to you then please do apply it.

I was just worried that there may be some subtle reason for why
ath11k_dp_pdev_alloc() was called after netdev registration in the first
place and that it might need to be split up so that for example
ath11k_dp_rx_pdev_mon_attach() isn't called until after registration.

I did not see this issue with next-20220310, but I hit it on every probe
with next-20220511. Perhaps some timing changed in between.

Here's the backtrace for completeness in case someone else starts hitting
this and searches the archives:

[   51.346947] kernel BUG at kernel/time/timer.c:990!
[   51.346958] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
...
[   51.578225] Call trace:
[   51.583293]  __mod_timer+0x298/0x390
[   51.589518]  mod_timer+0x14/0x20
[   51.595368]  ath11k_mac_op_start+0x41c/0x4a0 [ath11k]
[   51.603165]  drv_start+0x38/0x60 [mac80211]
[   51.610110]  ieee80211_do_open+0x29c/0x7d0 [mac80211]
[   51.617945]  ieee80211_open+0x60/0xb0 [mac80211]
[   51.625311]  __dev_open+0x100/0x1c0
[   51.631420]  __dev_change_flags+0x194/0x210
[   51.638214]  dev_change_flags+0x24/0x70
[   51.644646]  do_setlink+0x228/0xdb0
[   51.650723]  __rtnl_newlink+0x460/0x830
[   51.657162]  rtnl_newlink+0x4c/0x80
[   51.663229]  rtnetlink_rcv_msg+0x124/0x390
[   51.669917]  netlink_rcv_skb+0x58/0x130
[   51.676314]  rtnetlink_rcv+0x18/0x30
[   51.682460]  netlink_unicast+0x250/0x310
[   51.688960]  netlink_sendmsg+0x19c/0x3e0
[   51.695458]  ____sys_sendmsg+0x220/0x290
[   51.701938]  ___sys_sendmsg+0x7c/0xc0
[   51.708148]  __sys_sendmsg+0x68/0xd0
[   51.714254]  __arm64_sys_sendmsg+0x28/0x40
[   51.720900]  invoke_syscall+0x48/0x120

Johan