Re: [PATCH v7.2-rc6] drm/amd/display: fix usage of DC_FPU_{BEGIN,END} with PREEMPT_RT

[Greg KH]

On Fri, Aug 07, 2026 at 02:49:42PM +0200, Bert Karwatzki wrote:
> On PREEMPT_RT kernels kvzalloc_obj() can sleep because spin_lock is
> converted to rt_mutex. dc_create_plane_state() can be called while
> inside an FPU-guarded region, resuling in "scheduling while atomic"
> errors on PREEMPT_RT kernels.
>  Fix this by calling kvzalloc_obj() with DC_RUN_WITH_PREEMPTION_ENABLED().
> Also fix the error path in dc_create_stream_for_sink().
> 
> Fixes: 3539437f354b ("drm/amd/display: Move FPU Guards From DML To DC - Part 1")
> Link: https://lore.kernel.org/lkml/20260723123449.6494-1-spasswolf@xxxxxx/
> Signed-off-by: Bert Karwatzki <spasswolf@xxxxxx>
> ---
>  drivers/gpu/drm/amd/display/dc/core/dc_stream.c  | 5 +++--
>  drivers/gpu/drm/amd/display/dc/core/dc_surface.c | 5 +++--
>  2 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_stream.c b/drivers/gpu/drm/amd/display/dc/core/dc_stream.c
> index 7666cdc78f4e..a5a304a3f802 100644
> --- a/drivers/gpu/drm/amd/display/dc/core/dc_stream.c
> +++ b/drivers/gpu/drm/amd/display/dc/core/dc_stream.c
> @@ -233,8 +233,9 @@ struct dc_stream_state *dc_create_stream_for_sink(
>  
>  fail:
>  	if (stream) {
> -		kfree(stream->update_scratch);
> -		kfree(stream);
> +		if (stream->update_scratch)
> +			DC_RUN_WITH_PREEMPTION_ENABLED(kfree(stream->update_scratch));
> +		DC_RUN_WITH_PREEMPTION_ENABLED(kfree(stream));
>  	}
>  
>  	return NULL;
> diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_surface.c b/drivers/gpu/drm/amd/display/dc/core/dc_surface.c
> index 72845fc788f3..04982673ffbc 100644
> --- a/drivers/gpu/drm/amd/display/dc/core/dc_surface.c
> +++ b/drivers/gpu/drm/amd/display/dc/core/dc_surface.c
> @@ -33,6 +33,7 @@
>  #include "dpp.h"
>  
>  #include "dc_plane_priv.h"
> +#include "dc_fpu.h"
>  
>  /*******************************************************************************
>   * Private functions
> @@ -86,8 +87,8 @@ uint8_t  dc_plane_get_pipe_mask(struct dc_state *dc_state, const struct dc_plane
>   ******************************************************************************/
>  struct dc_plane_state *dc_create_plane_state(const struct dc *dc)
>  {
> -	struct dc_plane_state *plane_state = kvzalloc_obj(*plane_state,
> -							  GFP_ATOMIC);
> +	struct dc_plane_state *plane_state;
> +	DC_RUN_WITH_PREEMPTION_ENABLED(plane_state = kvzalloc_obj(*plane_state, GFP_ATOMIC));
>  
>  	if (NULL == plane_state)
>  		return NULL;
> -- 
> 2.55.0
> 
> Fix for stable with the old error handling in
> dc_create_stream_for_sink() and compile fix form arm64/clang.
> 
> Bert Karwatzki
> 

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>