Hi,
> media: v4l2-mem2mem: fix mem order in last buf
mem order ? Did you mean call order ?
Le dimanche 11 février 2024 à 02:04 +0800, Hsia-Jun Li a écrit :
> From: "Hsia-Jun(Randy) Li" <randy.li@xxxxxxxxxxxxx>
>
> The has_stopped property in struct v4l2_m2m_ctx is operated
> without a lock protecction. Then the userspace calls to
protection When ? ~~
> v4l2_m2m_encoder_cmd()/v4l2_m2m_decoder_cmd() may lead to
> a critical section issue.
As there is no locking, there is no critical section, perhaps a better phrasing
could help.
>
> Signed-off-by: Hsia-Jun(Randy) Li <randy.li@xxxxxxxxxxxxx>
> ---
> drivers/media/v4l2-core/v4l2-mem2mem.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c
> index 75517134a5e9..f1de71031e02 100644
> --- a/drivers/media/v4l2-core/v4l2-mem2mem.c
> +++ b/drivers/media/v4l2-core/v4l2-mem2mem.c
> @@ -635,9 +635,9 @@ void v4l2_m2m_last_buffer_done(struct v4l2_m2m_ctx *m2m_ctx,
> struct vb2_v4l2_buffer *vbuf)
> {
> vbuf->flags |= V4L2_BUF_FLAG_LAST;
> - vb2_buffer_done(&vbuf->vb2_buf, VB2_BUF_STATE_DONE);
> -
> v4l2_m2m_mark_stopped(m2m_ctx);
> +
> + vb2_buffer_done(&vbuf->vb2_buf, VB2_BUF_STATE_DONE);
While it most likely fix the issue while testing, since userspace most likely
polls on that queue and don't touch the driver until the poll was signalled, I
strongly believe this is insufficient. When I look at vicodec and wave5, they
both add a layer of locking on top of the mem2mem framework to fix this issue.
I think this is unfortunate, but v4l2_m2m_mark_stopped() is backed by 3 booleans
accessed in many places that aren't in any known atomic context. I think it
would be nice to remove the spurious locking in drivers and try and fix this
issue in the framework itself.
Nicolas
> }
> EXPORT_SYMBOL_GPL(v4l2_m2m_last_buffer_done);
>
