linux-kernel - Re: [PATCH v2 2/7] serial: qcom-geni: fix shutdown race

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Message-ID: <CAD=FV=UoU5Nd7sW66cjQzor+BP+W_f7uw0MGRaF6y7PH7KRN_g@mail.gmail.com>
Date: Thu, 3 Oct 2024 11:30:08 -0700
From: Doug Anderson <dianders@...omium.org>
To: Johan Hovold <johan+linaro@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jiri Slaby <jirislaby@...nel.org>, 
	Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konradybcio@...nel.org>, 
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-serial@...r.kernel.org, stable@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v2 2/7] serial: qcom-geni: fix shutdown race

Hi,

On Tue, Oct 1, 2024 at 5:51 AM Johan Hovold <johan+linaro@...nel.org> wrote:
>
> A commit adding back the stopping of tx on port shutdown failed to add
> back the locking which had also been removed by commit e83766334f96
> ("tty: serial: qcom_geni_serial: No need to stop tx/rx on UART
> shutdown").

Hmmm, when I look at that commit it makes me think that the problem
that commit e83766334f96 ("tty: serial: qcom_geni_serial: No need to
stop tx/rx on UART shutdown") was fixing was re-introduced by commit
d8aca2f96813 ("tty: serial: qcom-geni-serial: stop operations in
progress at shutdown"). ...and indeed, it was. :(

I can't interact with kgdb if I do this:

1. ssh over to DUT
2. Kill the console process (on ChromeOS stop console-ttyMSM0)
3. Drop in the debugger (echo g > /proc/sysrq-trigger)

This bug predates your series, but since it touches the same code
maybe you could fix it at the same time? I will note that commit
e83766334f96 ("tty: serial: qcom_geni_serial: No need to stop tx/rx on
UART shutdown") mentions that it wasn't required for FIFO mode--only
DMA...

Aside from the pre-existing bug, I agree that the locking should be there.

-Doug