Re: [PATCH 1/2] media: verisilicon: fix excessive stack usage

[Hans Verkuil]

Hi all,

On 6/28/23 20:26, Nathan Chancellor wrote:
> On Fri, Jun 16, 2023 at 04:48:47PM +0200, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@xxxxxxxx>
> >
> > In some configurations, gcc decides not to inline the register accessor functions,
> > which in turn leads to lots of temporary hantro_reg structures on the stack that
> > cannot be eliminated because they escape into an uninlined function:
> >
> > drivers/media/platform/verisilicon/rockchip_vpu981_hw_av1_dec.c:1022:1: warning: the frame size of 1112 bytes is larger than 1024 bytes [-Wframe-larger-than=]
> >
> > Mark all of these as __always_inline so the compiler is able to completely
> > eliminate the temporary structures instead, which brings the stack usage
> > back down to just the normal local variables.
> >
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > Closes: https://lore.kernel.org/oe-kbuild-all/202306151506.goHEegOd-lkp@xxxxxxxxx/
> > Fixes: 727a400686a2c ("media: verisilicon: Add Rockchip AV1 decoder")
> > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
>
> For what it's worth, this patch massively helps with avoiding a warning
> with clang 16.x and older, for presumably a similar reason, since this
> happens with allmodconfig, which turns on a bunch of sanitizers.
>
> https://github.com/ClangBuiltLinux/linux/issues/1875
>
> Before this change:
>
>    drivers/media/platform/verisilicon/rockchip_vpu981_hw_av1_dec.c:2097:5: error: stack frame size (2096) exceeds limit (2048) in 'rockchip_vpu981_av1_dec_run' [-Werror,-Wframe-larger-than]
>    int rockchip_vpu981_av1_dec_run(struct hantro_ctx *ctx)
>        ^
>    238/2096 (11.35%) spills, 1858/2096 (88.65%) variables
>
> After this change:
>
>    drivers/media/platform/verisilicon/rockchip_vpu981_hw_av1_dec.c:2097:5: error: stack frame size (496) exceeds limit (200) in 'rockchip_vpu981_av1_dec_run' [-Werror,-Wframe-larger-than]
>    int rockchip_vpu981_av1_dec_run(struct hantro_ctx *ctx)
>        ^
>    265/496 (53.43%) spills, 231/496 (46.57%) variables
>
> If this could be picked up either before the 6.5 media pull goes out or
> at some point during the -rc cycle, that would be great!

Once the merge window closes I'll make a PR to get it in 6.5.

Regards,

	Hans

> Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
>
> > ---
> >   drivers/media/platform/verisilicon/hantro.h | 22 ++++++++++-----------
> >   1 file changed, 11 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/media/platform/verisilicon/hantro.h b/drivers/media/platform/verisilicon/hantro.h
> > index 6523ffb748812..6c5e56ce5b351 100644
> > --- a/drivers/media/platform/verisilicon/hantro.h
> > +++ b/drivers/media/platform/verisilicon/hantro.h
> > @@ -370,26 +370,26 @@ extern int hantro_debug;
> >   	pr_err("%s:%d: " fmt, __func__, __LINE__, ##args)
> >   
> >   /* Structure access helpers. */
> > -static inline struct hantro_ctx *fh_to_ctx(struct v4l2_fh *fh)
> > +static __always_inline struct hantro_ctx *fh_to_ctx(struct v4l2_fh *fh)
> >   {
> >   	return container_of(fh, struct hantro_ctx, fh);
> >   }
> >   
> >   /* Register accessors. */
> > -static inline void vepu_write_relaxed(struct hantro_dev *vpu,
> > +static __always_inline void vepu_write_relaxed(struct hantro_dev *vpu,
> >   				      u32 val, u32 reg)
> >   {
> >   	vpu_debug(6, "0x%04x = 0x%08x\n", reg / 4, val);
> >   	writel_relaxed(val, vpu->enc_base + reg);
> >   }
> >   
> > -static inline void vepu_write(struct hantro_dev *vpu, u32 val, u32 reg)
> > +static __always_inline void vepu_write(struct hantro_dev *vpu, u32 val, u32 reg)
> >   {
> >   	vpu_debug(6, "0x%04x = 0x%08x\n", reg / 4, val);
> >   	writel(val, vpu->enc_base + reg);
> >   }
> >   
> > -static inline u32 vepu_read(struct hantro_dev *vpu, u32 reg)
> > +static __always_inline u32 vepu_read(struct hantro_dev *vpu, u32 reg)
> >   {
> >   	u32 val = readl(vpu->enc_base + reg);
> >   
> > @@ -397,27 +397,27 @@ static inline u32 vepu_read(struct hantro_dev *vpu, u32 reg)
> >   	return val;
> >   }
> >   
> > -static inline void vdpu_write_relaxed(struct hantro_dev *vpu,
> > +static __always_inline void vdpu_write_relaxed(struct hantro_dev *vpu,
> >   				      u32 val, u32 reg)
> >   {
> >   	vpu_debug(6, "0x%04x = 0x%08x\n", reg / 4, val);
> >   	writel_relaxed(val, vpu->dec_base + reg);
> >   }
> >   
> > -static inline void vdpu_write(struct hantro_dev *vpu, u32 val, u32 reg)
> > +static __always_inline void vdpu_write(struct hantro_dev *vpu, u32 val, u32 reg)
> >   {
> >   	vpu_debug(6, "0x%04x = 0x%08x\n", reg / 4, val);
> >   	writel(val, vpu->dec_base + reg);
> >   }
> >   
> > -static inline void hantro_write_addr(struct hantro_dev *vpu,
> > +static __always_inline void hantro_write_addr(struct hantro_dev *vpu,
> >   				     unsigned long offset,
> >   				     dma_addr_t addr)
> >   {
> >   	vdpu_write(vpu, addr & 0xffffffff, offset);
> >   }
> >   
> > -static inline u32 vdpu_read(struct hantro_dev *vpu, u32 reg)
> > +static __always_inline u32 vdpu_read(struct hantro_dev *vpu, u32 reg)
> >   {
> >   	u32 val = readl(vpu->dec_base + reg);
> >   
> > @@ -425,7 +425,7 @@ static inline u32 vdpu_read(struct hantro_dev *vpu, u32 reg)
> >   	return val;
> >   }
> >   
> > -static inline u32 vdpu_read_mask(struct hantro_dev *vpu,
> > +static __always_inline u32 vdpu_read_mask(struct hantro_dev *vpu,
> >   				 const struct hantro_reg *reg,
> >   				 u32 val)
> >   {
> > @@ -437,14 +437,14 @@ static inline u32 vdpu_read_mask(struct hantro_dev *vpu,
> >   	return v;
> >   }
> >   
> > -static inline void hantro_reg_write(struct hantro_dev *vpu,
> > +static __always_inline void hantro_reg_write(struct hantro_dev *vpu,
> >   				    const struct hantro_reg *reg,
> >   				    u32 val)
> >   {
> >   	vdpu_write_relaxed(vpu, vdpu_read_mask(vpu, reg, val), reg->base);
> >   }
> >   
> > -static inline void hantro_reg_write_s(struct hantro_dev *vpu,
> > +static __always_inline void hantro_reg_write_s(struct hantro_dev *vpu,
> >   				      const struct hantro_reg *reg,
> >   				      u32 val)
> >   {
> > --
> > 2.39.2