linux-kernel - Re: [PATCH 0/3] ath9k: interrupt fixes on queue reset

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Date:   Wed, 15 Sep 2021 11:23:43 +0200
From:   Linus Lüssing <linus.luessing@...3.blue>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Kalle Valo <kvalo@...eaurora.org>, Felix Fietkau <nbd@....name>,
        Sujith Manoharan <c_manoha@....qualcomm.com>,
        ath9k-devel@....qualcomm.com, linux-wireless@...r.kernel.org,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "John W . Linville" <linville@...driver.com>,
        Felix Fietkau <nbd@...nwrt.org>,
        Simon Wunderlich <sw@...onwunderlich.de>,
        Sven Eckelmann <sven@...fation.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] ath9k: interrupt fixes on queue reset

Hi Toke,

On Tue, Sep 14, 2021 at 09:53:34PM +0200, Toke Høiland-Jørgensen wrote:
> Linus Lüssing <linus.luessing@...3.blue> writes:
> 
> > Hi,
> >
> > The following are two patches for ath9k to fix a potential interrupt
> > storm (PATCH 2/3) and to fix potentially resetting the wifi chip while
> > its interrupts were accidentally reenabled (PATCH 3/3).
> 
> Uhh, interesting - nice debugging work! What's the user-level symptom of
> this? I.e., when this triggers does the device just appear to hang, or
> does it cause reboots, or?
> 
> -Toke
> 

For PATCH 2/3 the user-level symptom was that the system would
hang for a few seconds and would then silently reboot without any notice
on the serial console. And after disabling CONFIG_ATH79_WDT the
system would "hang" indefinitely without any notice on the console
without a reboot (while JTAG/gdb showed that it was entering ath_isr()
again and again and wasn't doing anything else).

For PATCH 3/3 I don't have a specific user-level symptom. But from
looking at the git history it seemed to me that the ath9k hw
interrupts (AR_IER, AR_INTR_ASYNC_ENABLE and AR_INTR_ASYNC_ENABLE off)
should be disabled during a reset:

  4668cce527ac ath9k: disable the tasklet before taking the PCU lock
  eaf04a691566 ath9k: Disable beacon tasklet during reset
  872b5d814f99 ath9k: do not access hardware on IRQs during reset
  e3f31175a3ee ath9k: fix race condition in irq processing during hardware reset

Maybe someone else on these lists might know what issues this can
cause exactly?

Regards, Linus