linux-kernel - Re: [PATCH v2] media: mediatek: vcodec: Use spinlock for context list protection lock

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Message-ID: <CAC=S1njQ5z2Ezz2OXDJ6Pk_9EEPgG3gu=Os7uFv6Lmdq0X77og@mail.gmail.com>
Date: Wed, 20 Aug 2025 18:36:55 +0800
From: Fei Shao <fshao@...omium.org>
To: Chen-Yu Tsai <wenst@...omium.org>
Cc: Yunfei Dong <yunfei.dong@...iatek.com>, Mauro Carvalho Chehab <mchehab@...nel.org>, 
	Hans Verkuil <hverkuil@...all.nl>, Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, linux-media@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org, 
	Tomasz Figa <tfiga@...omium.org>
Subject: Re: [PATCH v2] media: mediatek: vcodec: Use spinlock for context list
 protection lock

On Wed, Aug 20, 2025 at 3:54 PM Chen-Yu Tsai <wenst@...omium.org> wrote:
>
> Previously a mutex was added to protect the encoder and decoder context
> lists from unexpected changes originating from the SCP IP block, causing
> the context pointer to go invalid, resulting in a NULL pointer
> dereference in the IPI handler.
>
> Turns out on the MT8173, the VPU IPI handler is called from hard IRQ
> context. This causes a big warning from the scheduler. This was first
> reported downstream on the ChromeOS kernels, but is also reproducible
> on mainline using Fluster with the FFmpeg v4l2m2m decoders. Even though
> the actual capture format is not supported, the affected code paths
> are triggered.
>
> Since this lock just protects the context list and operations on it are
> very fast, it should be OK to switch to a spinlock.
>
> Fixes: 6467cda18c9f ("media: mediatek: vcodec: adding lock to protect decoder context list")
> Fixes: afaaf3a0f647 ("media: mediatek: vcodec: adding lock to protect encoder context list")
> Cc: Yunfei Dong <yunfei.dong@...iatek.com>
> Signed-off-by: Chen-Yu Tsai <wenst@...omium.org>
> ---
> Changes since v1:
> - Switched to _irqsave / _irqrestore variants even in helper only called
>   by IRQ handler (Tomasz)
>
>  .../mediatek/vcodec/common/mtk_vcodec_fw_vpu.c       | 10 ++++++----
>  .../mediatek/vcodec/decoder/mtk_vcodec_dec_drv.c     | 12 +++++++-----
>  .../mediatek/vcodec/decoder/mtk_vcodec_dec_drv.h     |  2 +-
>  .../platform/mediatek/vcodec/decoder/vdec_vpu_if.c   |  5 +++--
>  .../mediatek/vcodec/encoder/mtk_vcodec_enc_drv.c     | 12 +++++++-----
>  .../mediatek/vcodec/encoder/mtk_vcodec_enc_drv.h     |  2 +-
>  .../platform/mediatek/vcodec/encoder/venc_vpu_if.c   |  5 +++--
>  7 files changed, 28 insertions(+), 20 deletions(-)

Reviewed-by: Fei Shao <fshao@...omium.org>