Re: [PATCH] venus: avoid extra locking in driver

From: Jeffrey Kardatzke
Date: Mon Mar 09 2020 - 18:07:31 EST

On Thu, Mar 5, 2020 at 11:50 PM Alexandre Courbot <acourbot@xxxxxxxxxxxx> wrote:
>
> On Fri, Mar 6, 2020 at 2:34 PM Mansur Alisha Shaik
> <mansur@xxxxxxxxxxxxxx> wrote:
> >
> > This change will avoid extra locking in driver.
>
> Could you elaborate a bit more on the problem that this patch solves?

For us it fixes a kernel null deref that happens when we run the
MultipleEncoders test (I've verified this to be true).

>
> >
> > Signed-off-by: Mansur Alisha Shaik <mansur@xxxxxxxxxxxxxx>
> > ---
> > drivers/media/platform/qcom/venus/core.c | 2 +-
> > drivers/media/platform/qcom/venus/core.h | 2 +-
> > drivers/media/platform/qcom/venus/helpers.c | 11 +++++++++--
> > drivers/media/platform/qcom/venus/pm_helpers.c | 8 ++++----
> > 4 files changed, 15 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/media/platform/qcom/venus/core.c b/drivers/media/platform/qcom/venus/core.c
> > index 194b10b9..75d38b8 100644
> > --- a/drivers/media/platform/qcom/venus/core.c
> > +++ b/drivers/media/platform/qcom/venus/core.c
> > @@ -447,7 +447,7 @@ static const struct freq_tbl sdm845_freq_table[] = {
> > { 244800, 100000000 }, /* 1920x1080@30 */
> > };
> >
> > -static struct codec_freq_data sdm845_codec_freq_data[] = {
> > +static const struct codec_freq_data sdm845_codec_freq_data[] = {
> > { V4L2_PIX_FMT_H264, VIDC_SESSION_TYPE_ENC, 675, 10 },
> > { V4L2_PIX_FMT_HEVC, VIDC_SESSION_TYPE_ENC, 675, 10 },
> > { V4L2_PIX_FMT_VP8, VIDC_SESSION_TYPE_ENC, 675, 10 },
> > diff --git a/drivers/media/platform/qcom/venus/core.h b/drivers/media/platform/qcom/venus/core.h
> > index ab7c360..8c8d0e9 100644
> > --- a/drivers/media/platform/qcom/venus/core.h
> > +++ b/drivers/media/platform/qcom/venus/core.h
> > @@ -245,7 +245,7 @@ struct venus_buffer {
> > struct clock_data {
> > u32 core_id;
> > unsigned long freq;
> > - const struct codec_freq_data *codec_freq_data;
> > + struct codec_freq_data codec_freq_data;
> > };
> >
> > #define to_venus_buffer(ptr) container_of(ptr, struct venus_buffer, vb)
> > diff --git a/drivers/media/platform/qcom/venus/helpers.c b/drivers/media/platform/qcom/venus/helpers.c
> > index bcc6038..550c4ff 100644
> > --- a/drivers/media/platform/qcom/venus/helpers.c
> > +++ b/drivers/media/platform/qcom/venus/helpers.c
> > @@ -807,6 +807,7 @@ int venus_helper_init_codec_freq_data(struct venus_inst *inst)
> > unsigned int i, data_size;
> > u32 pixfmt;
> > int ret = 0;
> > + bool found = false;
> >
> > if (!IS_V4(inst->core))
> > return 0;
> > @@ -816,16 +817,22 @@ int venus_helper_init_codec_freq_data(struct venus_inst *inst)
> > pixfmt = inst->session_type == VIDC_SESSION_TYPE_DEC ?
> > inst->fmt_out->pixfmt : inst->fmt_cap->pixfmt;
> >
> > + memset(&inst->clk_data.codec_freq_data, 0,
> > + sizeof(inst->clk_data.codec_freq_data));
> > +
> > for (i = 0; i < data_size; i++) {
> > if (data[i].pixfmt == pixfmt &&
> > data[i].session_type == inst->session_type) {
> > - inst->clk_data.codec_freq_data = &data[i];
> > + inst->clk_data.codec_freq_data = data[i];
>
> From the patch I'd infer that inst->clk_data.codec_freq_data needs to
> change at runtime. Is this what happens? Why? I'd expect that
> frequency tables remain constant, and thus that the global
> sdm845_codec_freq_data can remain constant while
> clock_data::codec_freq_data is a const reference to it. What prevents
> this from happening?
>
> > + found = true;
> > break;
> > }
> > }
> >
> > - if (!inst->clk_data.codec_freq_data)
> > + if (!found) {
> > + dev_err(inst->core->dev, "cannot find codec freq data\n");
> > ret = -EINVAL;
> > + }
> >
> > return ret;
> > }
> > diff --git a/drivers/media/platform/qcom/venus/pm_helpers.c b/drivers/media/platform/qcom/venus/pm_helpers.c
> > index abf9315..240845e 100644
> > --- a/drivers/media/platform/qcom/venus/pm_helpers.c
> > +++ b/drivers/media/platform/qcom/venus/pm_helpers.c
> > @@ -496,7 +496,7 @@ min_loaded_core(struct venus_inst *inst, u32 *min_coreid, u32 *min_load)
> > list_for_each_entry(inst_pos, &core->instances, list) {
> > if (inst_pos == inst)
> > continue;
> > - vpp_freq = inst_pos->clk_data.codec_freq_data->vpp_freq;
> > + vpp_freq = inst_pos->clk_data.codec_freq_data.vpp_freq;

This is the main thing it fixes (this is where the null deref occurs).
If there's multiple instances in use and the other instance hasn't
populated the codec_freq_data pointer then we'll hit a null deref
here.

> > coreid = inst_pos->clk_data.core_id;
> >
> > mbs_per_sec = load_per_instance(inst_pos);
> > @@ -545,7 +545,7 @@ static int decide_core(struct venus_inst *inst)
> > return 0;
> >
> > inst_load = load_per_instance(inst);
> > - inst_load *= inst->clk_data.codec_freq_data->vpp_freq;
> > + inst_load *= inst->clk_data.codec_freq_data.vpp_freq;
> > max_freq = core->res->freq_tbl[0].freq;
> >
> > min_loaded_core(inst, &min_coreid, &min_load);
> > @@ -848,10 +848,10 @@ static unsigned long calculate_inst_freq(struct venus_inst *inst,
> >
> > mbs_per_sec = load_per_instance(inst) / fps;
> >
> > - vpp_freq = mbs_per_sec * inst->clk_data.codec_freq_data->vpp_freq;
> > + vpp_freq = mbs_per_sec * inst->clk_data.codec_freq_data.vpp_freq;
> > /* 21 / 20 is overhead factor */
> > vpp_freq += vpp_freq / 20;
> > - vsp_freq = mbs_per_sec * inst->clk_data.codec_freq_data->vsp_freq;
> > + vsp_freq = mbs_per_sec * inst->clk_data.codec_freq_data.vsp_freq;
> >
> > /* 10 / 7 is overhead factor */
> > if (inst->session_type == VIDC_SESSION_TYPE_ENC)
> > --
> > 2.7.4
> >



--
Jeffrey Kardatzke
jkardatzke@xxxxxxxxxx
Google, Inc.