linux-kernel - Re: [PATCH v3] Bluetooth: hci_qca: Bug fixes while collecting controller memory dump

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Date:   Thu, 13 Feb 2020 18:22:56 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     Venkata Lakshmi Narayana Gubba <gubbaven@...eaurora.org>,
        johan.hedberg@...il.com, marcel@...tmann.org
Cc:     mka@...omium.org, linux-kernel@...r.kernel.org,
        linux-bluetooth@...r.kernel.org, robh@...nel.org,
        hemantg@...eaurora.org, linux-arm-msm@...r.kernel.org,
        bgodavar@...eaurora.org, tientzu@...omium.org,
        seanpaul@...omium.org, rjliao@...eaurora.org, yshavit@...gle.com,
        Venkata Lakshmi Narayana Gubba <gubbaven@...eaurora.org>
Subject: Re: [PATCH v3] Bluetooth: hci_qca: Bug fixes while collecting controller memory dump

Quoting Venkata Lakshmi Narayana Gubba (2020-02-13 07:56:04)
> This patch will fix the below issues
>    1.Fixed race conditions while accessing memory dump state flags.

What sort of race condition?

>    2.Updated with actual context of timer in hci_memdump_timeout()

What does this mean?

>    3.Updated injecting hardware error event if the dumps failed to receive.
>    4.Once timeout is triggered, stopping the memory dump collections.
> 
> Possible scenarios while collecting memory dump:
> 
> Scenario 1:
> 
> Memdump event from firmware
> Some number of memdump events with seq #
> Hw error event
> Reset
> 
> Scenario 2:
> 
> Memdump event from firmware
> Some number of memdump events with seq #
> Timeout schedules hw_error_event if hw error event is not received already
> hw_error_event clears the memdump activity
> reset
> 
> Scenario 3:
> 
> hw_error_event sends memdump command to firmware and waits for completion
> Some number of memdump events with seq #
> hw error event
> reset
> 
> Fixes: d841502c79e3 ("Bluetooth: hci_qca: Collect controller memory dump during SSR")
> Reported-by: Abhishek Pandit-Subedi <abhishekpandit@...omium.org>
> Signed-off-by: Venkata Lakshmi Narayana Gubba <gubbaven@...eaurora.org>
> ---
[...]
> @@ -1449,6 +1465,23 @@ static void qca_hw_error(struct hci_dev *hdev, u8 code)
>                 bt_dev_info(hdev, "waiting for dump to complete");
>                 qca_wait_for_dump_collection(hdev);
>         }
> +
> +       if (qca->memdump_state != QCA_MEMDUMP_COLLECTED) {
> +               bt_dev_err(hu->hdev, "clearing allocated memory due to memdump timeout");
> +               mutex_lock(&qca->hci_memdump_lock);

Why is a mutex needed? Are crashes happening in parallel? It would be
nice if the commit text mentioned why the mutex is added so that the
reader doesn't have to figure it out.

> +               if (qca_memdump)
> +                       memdump_buf = qca_memdump->memdump_buf_head;