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/[email protected]/
> Signed-off-by: Bert Karwatzki <[email protected]>
> ---
> 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>
