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From:   Kalle Valo <kvalo@codeaurora.org>
To:     Erik Stromdahl <erik.stromdahl@gmail.com>
Cc:     linux-wireless@vger.kernel.org, ath10k@lists.infradead.org
Subject: Re: [PATCH v2 5/5] ath10k: sdio: remove skb_trim in TX path
References: <20190417191503.18814-1-erik.stromdahl@gmail.com>
        <20190417191503.18814-6-erik.stromdahl@gmail.com>
Date:   Tue, 01 Oct 2019 15:22:52 +0300
In-Reply-To: <20190417191503.18814-6-erik.stromdahl@gmail.com> (Erik
        Stromdahl's message of "Wed, 17 Apr 2019 21:15:03 +0200")
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Erik Stromdahl <erik.stromdahl@gmail.com> writes:

> This patch fixes a bug with padding of the skb data buffer.
> Since skb_trim can only be used to reduce the skb len, it is useless when
> we pad (increase the length of) the skb. Instead we allocate a new
> buffer with enough space to contain both the TX data and padding.
>
> Since some skb's have multiple references, we can't use skb_put_padto()
> to extend and pad skb->data (since it causes a panic if there is more
> than one reference).
>
> Also, in order to avoid the following possible deadlock issue (reported by
> lockdep):
>
> [   26.508508]  Possible interrupt unsafe locking scenario:
> [   26.508508]
> [   26.515314]        CPU0                    CPU1
> [   26.519862]        ----                    ----
> [   26.524408]   lock(fs_reclaim);
> [   26.527573]                                local_irq_disable();
> [   26.533508]                                lock(_xmit_ETHER#2);
> [   26.539453]                                lock(fs_reclaim);
> [   26.545135]   <Interrupt>
> [   26.547769]     lock(_xmit_ETHER#2);
> [   26.551370]
> [   26.551370]  *** DEADLOCK ***
>
> ... we use the GFP_NOFS flag with kzalloc()
>
> Signed-off-by: Erik Stromdahl <erik.stromdahl@gmail.com>

I replied to v1 about using skb_pad(), let's discuss more there:

https://patchwork.kernel.org/patch/10891949/

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