[PATCH] drm/amd/display: fix usage of DC_FPU_{BEGIN,END} with PREEMPT_RT

[PATCH] drm/amd/display: fix usage of DC_FPU_{BEGIN,END} with PREEMPT_RT

[Bert Karwatzki]

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@web.de/

Signed-off-by: Bert Karwatzki <spasswolf@web.de>
---
 drivers/gpu/drm/amd/display/dc/core/dc_stream.c  | 5 +++--
 drivers/gpu/drm/amd/display/dc/core/dc_surface.c | 4 ++--
 2 files changed, 5 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 dbc12640b01c..4ac835777b58 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 88e825a6582c..d5c6427796b6 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_surface.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_surface.c
@@ -85,8 +85,8 @@ 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;
-- 
2.53.0

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

[mikhail.v.gavrilov]

On Mon, 2026-07-27 at 12:50 +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@web.de/
> 
> Signed-off-by: Bert Karwatzki <spasswolf@web.de>
> ---
>  drivers/gpu/drm/amd/display/dc/core/dc_stream.c  | 5 +++--
>  drivers/gpu/drm/amd/display/dc/core/dc_surface.c | 4 ++--
>  2 files changed, 5 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 dbc12640b01c..4ac835777b58 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 88e825a6582c..d5c6427796b6 100644
> --- a/drivers/gpu/drm/amd/display/dc/core/dc_surface.c
> +++ b/drivers/gpu/drm/amd/display/dc/core/dc_surface.c
> @@ -85,8 +85,8 @@ 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;

Hi Bert,

You may not be aware that the same allocation is already wrapped once,
at the dcn32 call site:

  183182235f6d ("drm/amd/display: Wrap DCN32 phantom-plane allocation
in DC_RUN_WITH_PREEMPTION_ENABLED")

That one only covers the dcn32 DML1 path, while your trace goes through
dcn401_validate_bandwidth() and dml21 - so wrapping the call site could
never have caught your case.  Which is a good argument for guarding the
allocation in the callee, as you do: dc_create_plane_state() is reached
from every DCN and both DML generations.

On dcn32 the two wraps now nest.  That is harmless, because
DC_RUN_WITH_PREEMPTION_ENABLED() is conditional on dc_is_fp_enabled():
once the outer instance has left the FPU region, the inner one expands
to a plain call.  But it does make the dcn32 wrap redundant, and I
think it should be dropped in a follow-up now that the allocation is
guarded in the callee.

One thing that may be worth adjusting in the commit message: this is
not only a PREEMPT_RT problem.  183182235f6d was needed on a plain non-
RT x86 kernel. There DC_FP_START() takes fpregs_lock(), which disables
local softirqs, and dc_plane_state is around 335 KiB, so kvzalloc_obj()
falls through to the vmalloc path and hits BUG_ON(in_interrupt()).  So
on RT any allocation inside the FPU region is illegal, while on non-RT
it is specifically the large ones - two failure modes, one root cause.

About the FPU register question raised by the review bot: as far as I
can see it applies to every existing user of
DC_RUN_WITH_PREEMPTION_ENABLED(), 183182235f6d included, so it looks
like a property of the macro rather than something your patch
introduces.  An answer from AMD on that would be useful either way.

I have dcn32 hardware here (RX 7900 XTX) and can test the patch on
non-RT if that helps.

-- 
Thanks,
Mikhail

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

[Bert Karwatzki]

Am Dienstag, dem 28.07.2026 um 05:51 +0500 schrieb mikhail.v.gavrilov@gmail.com:
> On Mon, 2026-07-27 at 12:50 +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@web.de/
> > 
> > Signed-off-by: Bert Karwatzki <spasswolf@web.de>
> > ---
> >  drivers/gpu/drm/amd/display/dc/core/dc_stream.c  | 5 +++--
> >  drivers/gpu/drm/amd/display/dc/core/dc_surface.c | 4 ++--
> >  2 files changed, 5 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 dbc12640b01c..4ac835777b58 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 88e825a6582c..d5c6427796b6 100644
> > --- a/drivers/gpu/drm/amd/display/dc/core/dc_surface.c
> > +++ b/drivers/gpu/drm/amd/display/dc/core/dc_surface.c
> > @@ -85,8 +85,8 @@ 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;
> 
> Hi Bert,
> 
> You may not be aware that the same allocation is already wrapped once,
> at the dcn32 call site:
> 
>   183182235f6d ("drm/amd/display: Wrap DCN32 phantom-plane allocation
> in DC_RUN_WITH_PREEMPTION_ENABLED")
> 
> That one only covers the dcn32 DML1 path, while your trace goes through
> dcn401_validate_bandwidth() and dml21 - so wrapping the call site could
> never have caught your case.  Which is a good argument for guarding the
> allocation in the callee, as you do: dc_create_plane_state() is reached
> from every DCN and both DML generations.

I did try a different approach, using DC_RUN_WITH_PREEMPTION_ENABLED further
upward in the calltrace (This would have the slight benefit of more code
running with preemption enabled). This does not work because dml21_utils.c is compiled
as a _LINUX_FPU_COMPILATION_UNIT, so DC_RUN_WITH_PREEMPTION_ENABLED does nothing.
(see drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.h)

diff --git a/drivers/gpu/drm/amd/display/dc/dml2_0/dml21/dml21_utils.c b/drivers/gpu/drm/amd/display/dc/dml2_0/dml21/dml21_utils.c
index 835fece1d46a..8c92deded8cd 100644
--- a/drivers/gpu/drm/amd/display/dc/dml2_0/dml21/dml21_utils.c
+++ b/drivers/gpu/drm/amd/display/dc/dml2_0/dml21/dml21_utils.c
@@ -286,7 +286,8 @@ static struct dc_plane_state *dml21_add_phantom_plane(struct dml2_context *dml_c
        (void)plane_programming;
        struct dc_plane_state *phantom_plane;
 
-       phantom_plane = dml_ctx->config.svp_pstate.callbacks.create_phantom_plane(dc, context, main_plane);
+       DC_RUN_WITH_PREEMPTION_ENABLED(phantom_plane
+                       = dml_ctx->config.svp_pstate.callbacks.create_phantom_plane(dc, context, main_plane));
        if (!phantom_plane)
                return NULL;
 
diff --git a/drivers/gpu/drm/amd/display/dc/dml2_0/dml2_mall_phantom.c b/drivers/gpu/drm/amd/display/dc/dml2_0/dml2_mall_phantom.c
index 4543a60a0683..464bab9fc13b 100644
--- a/drivers/gpu/drm/amd/display/dc/dml2_0/dml2_mall_phantom.c
+++ b/drivers/gpu/drm/amd/display/dc/dml2_0/dml2_mall_phantom.c
@@ -769,10 +769,11 @@ static void enable_phantom_plane(struct dml2_context *ctx,
                if (curr_pipe->top_pipe && curr_pipe->top_pipe->plane_state == curr_pipe->plane_state) {
                        phantom_plane = prev_phantom_plane;
                } else {
-                       phantom_plane = ctx->config.svp_pstate.callbacks.create_phantom_plane(
+                       DC_RUN_WITH_PREEMPTION_ENABLED(phantom_plane =
+                                       ctx->config.svp_pstate.callbacks.create_phantom_plane(
                                        ctx->config.svp_pstate.callbacks.dc,
                                        state,
-                                       curr_pipe->plane_state);
+                                       curr_pipe->plane_state));
                        if (!phantom_plane)
                                return;
                }




Bert Karwatzki

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

[Mikhail Gavrilov]

On Wed, Jul 29, 2026 at 5:36 PM Bert Karwatzki <spasswolf@web.de> wrote:
>
> I did try a different approach, using DC_RUN_WITH_PREEMPTION_ENABLED further
> upward in the calltrace (This would have the slight benefit of more code
> running with preemption enabled). This does not work because dml21_utils.c is compiled
> as a _LINUX_FPU_COMPILATION_UNIT, so DC_RUN_WITH_PREEMPTION_ENABLED does nothing.

Confirmed, and the chain is worth spelling out because it is not obvious
from the call site:

  Makefile:1127:      CC_FLAGS_FPU += -D_LINUX_FPU_COMPILATION_UNIT
  dc/dml2_0/Makefile: applies $(CC_FLAGS_FPU) to every object under
                      dc/dml2_0/ ("Add FPU flags to all dml2 files by
                      default")

so both files you tried are built with -D_LINUX_FPU_COMPILATION_UNIT,
and in that branch of dc_fpu.h the macro is:

  #define DC_RUN_WITH_PREEMPTION_ENABLED(code) code

What I think is the real problem here: in the same branch DC_FP_START()
and DC_FP_END() are defined as BUILD_BUG(), so misusing those inside an
FPU compilation unit fails the build.  DC_RUN_WITH_PREEMPTION_ENABLED()
silently degrades to a plain call instead.  It compiles cleanly, looks
correct on review, and does nothing - which is exactly the trap you just
walked into.  Making it BUILD_BUG() as well would turn that into a
compile error.  I can send that as a separate patch if AMD agrees it is
the right direction.

This also explains the asymmetry with 183182235f6d: dc/resource/dcn32/
does not get the FPU flags, so the call-site wrap there expands to the
real thing, while the equivalent wrap in the dml21 path would have been
a no-op.  Another reason to guard the allocation in the callee, as your
patch does.

-- 
Thanks,
Mikhail

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

[Bert Karwatzki]

Am Dienstag, dem 28.07.2026 um 05:51 +0500 schrieb mikhail.v.gavrilov@gmail.com:
> One thing that may be worth adjusting in the commit message: this is
> not only a PREEMPT_RT problem.  183182235f6d was needed on a plain non-
> RT x86 kernel. There DC_FP_START() takes fpregs_lock(), which disables
> local softirqs, and dc_plane_state is around 335 KiB, so kvzalloc_obj()
> falls through to the vmalloc path and hits BUG_ON(in_interrupt()).  So
> on RT any allocation inside the FPU region is illegal, while on non-RT
> it is specifically the large ones - two failure modes, one root cause.

I think this was true when commit 
183182235f6d ("drm/amd/display: Wrap DCN32 phantom-plane allocation in DC_RUN_WITH_PREEMPTION_ENABLED")
was commited, but commit
04aa71da5f35 ("mm/vmalloc: do not trigger BUG() on BH disabled context")
changed the BUG_ON() in __get_vm_area_node():
diff --git a/mm/vmalloc.c b/mm/vmalloc.c

index c31a8615a832..bb6ae08d18f5 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3203,7 +3203,7 @@ struct vm_struct *__get_vm_area_node(unsigned long size,
        struct vm_struct *area;
        unsigned long requested_size = size;
 
-       BUG_ON(in_interrupt());
+       BUG_ON(in_nmi() || in_hardirq());
        size = ALIGN(size, 1ul << shift);
        if (unlikely(!size))
                return NULL;

so on non-PREEMPT_RT kernels DC_RUN_WITH_PREEMPTION_ENABLED is no
longer required for DCN32 phantom-plane allocation.

Bert Karwatzki

[PATCH] drm/amd/display: fix usage of DC_FPU_{BEGIN,END} with PREEMPT_RT

[Bert Karwatzki]

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@web.de/

Signed-off-by: Bert Karwatzki <spasswolf@web.de>
---
 drivers/gpu/drm/amd/display/dc/core/dc_stream.c  | 2 +-
 drivers/gpu/drm/amd/display/dc/core/dc_surface.c | 4 ++--
 2 files changed, 3 insertions(+), 3 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 cdcf140bc1bb..accad9e20e88 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_stream.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_stream.c
@@ -229,7 +229,7 @@ struct dc_stream_state *dc_create_stream_for_sink(
 
 fail:
 	if (stream)
-		kfree(stream);
+		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 88e825a6582c..d5c6427796b6 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_surface.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_surface.c
@@ -85,8 +85,8 @@ 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;
-- 
2.53.0


Rebased to next-20260729+. In these version the allocation of
update_scratch has been removed from dc_create_stream_for_sink().

Bert Karwatzki

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

[Mikhail Gavrilov]

On Sat, Aug 1, 2026 at 12:17 PM Bert Karwatzki <spasswolf@web.de> 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@web.de/
>
> Signed-off-by: Bert Karwatzki <spasswolf@web.de>
> ---
>  drivers/gpu/drm/amd/display/dc/core/dc_stream.c  | 2 +-
>  drivers/gpu/drm/amd/display/dc/core/dc_surface.c | 4 ++--
>  2 files changed, 3 insertions(+), 3 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 cdcf140bc1bb..accad9e20e88 100644
> --- a/drivers/gpu/drm/amd/display/dc/core/dc_stream.c
> +++ b/drivers/gpu/drm/amd/display/dc/core/dc_stream.c
> @@ -229,7 +229,7 @@ struct dc_stream_state *dc_create_stream_for_sink(
>
>  fail:
>         if (stream)
> -               kfree(stream);
> +               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 88e825a6582c..d5c6427796b6 100644
> --- a/drivers/gpu/drm/amd/display/dc/core/dc_surface.c
> +++ b/drivers/gpu/drm/amd/display/dc/core/dc_surface.c
> @@ -85,8 +85,8 @@ 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));


This hunk breaks the build when CONFIG_DRM_AMD_DC_FP=n.

dc_surface.c gets DC_RUN_WITH_PREEMPTION_ENABLED only indirectly, via
dc.h -> dc_types.h -> os_types.h, and there the include is guarded:

#if defined(CONFIG_DRM_AMD_DC_FP)
#include "amdgpu_dm/dc_fpu.h"
#endif

With DC_FP=n nothing defines the macro in that file.  dc_stream.c is not
affected because it includes dc_fpu.h directly.

This is not only exotic architectures: DRM_AMD_DC has

select DRM_AMD_DC_FP if ARCH_HAS_KERNEL_FPU_SUPPORT && \
!(CC_IS_CLANG && (ARM64 || LOONGARCH || RISCV))

so an arm64 clang build is enough.  On amd-staging-drm-next with your
patch applied:

  $ make LLVM=1 ARCH=arm64 allmodconfig
  $ make LLVM=1 ARCH=arm64 drivers/gpu/drm/amd/amdgpu/
  dc_surface.c:89:2: error: call to undeclared function
    'DC_RUN_WITH_PREEMPTION_ENABLED'; ISO C99 and later do not support
    implicit function declarations [-Wimplicit-function-declaration]
     89 |  DC_RUN_WITH_PREEMPTION_ENABLED(plane_state =
kvzalloc_obj(*plane_state, GFP_ATOMIC));

A plain x86_64 build (DC_FP=y) is clean, which is presumably why it did
not show up for you.

Adding

#include "dc_fpu.h"

to dc_surface.c fixes it, and matches what dc_stream.c already does.
Please do not copy the local fallback that sits below that include in
dc_stream.c:

#if !defined(DC_RUN_WITH_PREEMPTION_ENABLED)
#define DC_RUN_WITH_PREEMPTION_ENABLED(code) code
#endif

It is dead code there - dc_fpu.h defines the macro in every branch - and
in a new file it would compile cleanly while quietly doing nothing.

One unrelated note: you kept Cc: stable # v7.1, but this version is
rebased onto next-20260729, where the update_scratch allocation is gone
from dc_create_stream_for_sink().  It does not apply to current mainline
either, so older trees will need a separate backport - worth saying so
in the commit message.

With the include added I can give this a Tested-by on dcn32 (RX 7900
XTX), which exercises the DML1 phantom-plane path rather than the dml21
one you hit.

-- 
Best Regards,
Mikhail Gavrilov.

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

[kernel test robot]

Hi Bert,

kernel test robot noticed the following build errors:

[auto build test ERROR on next-20260804]
[cannot apply to drm-misc/drm-misc-next linus/master v7.2-rc6 v7.2-rc5 v7.2-rc4 v7.2-rc6]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Bert-Karwatzki/drm-amd-display-fix-usage-of-DC_FPU_-BEGIN-END-with-PREEMPT_RT/20260805-170330
base:   next-20260804
patch link:    https://lore.kernel.org/r/20260801071724.12998-1-spasswolf%40web.de
patch subject: [PATCH] drm/amd/display: fix usage of DC_FPU_{BEGIN,END} with PREEMPT_RT
config: loongarch-defconfig (https://download.01.org/0day-ci/archive/20260806/202608061154.QtrglsMo-lkp@intel.com/config)
compiler: clang version 24.0.0git (https://github.com/llvm/llvm-project bacfe2950f8218268fcc0a8765644ea0c15f0360)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260806/202608061154.QtrglsMo-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202608061154.QtrglsMo-lkp@intel.com/

All errors (new ones prefixed by >>):

>> drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_surface.c:89:2: error: call to undeclared function 'DC_RUN_WITH_PREEMPTION_ENABLED'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
      89 |         DC_RUN_WITH_PREEMPTION_ENABLED(plane_state = kvzalloc_obj(*plane_state, GFP_ATOMIC));
         |         ^
   1 error generated.


vim +/DC_RUN_WITH_PREEMPTION_ENABLED +89 drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_surface.c

    82	
    83	/*******************************************************************************
    84	 * Public functions
    85	 ******************************************************************************/
    86	struct dc_plane_state *dc_create_plane_state(const struct dc *dc)
    87	{
    88		struct dc_plane_state *plane_state;
  > 89		DC_RUN_WITH_PREEMPTION_ENABLED(plane_state = kvzalloc_obj(*plane_state, GFP_ATOMIC));
    90	
    91		if (NULL == plane_state)
    92			return NULL;
    93	
    94		kref_init(&plane_state->refcount);
    95		dc_plane_construct(dc->ctx, plane_state);
    96	
    97		return plane_state;
    98	}
    99	

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

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

[kernel test robot]

Hi Bert,

kernel test robot noticed the following build errors:

[auto build test ERROR on next-20260804]
[cannot apply to drm-misc/drm-misc-next linus/master v7.2-rc6 v7.2-rc5 v7.2-rc4 v7.2-rc6]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Bert-Karwatzki/drm-amd-display-fix-usage-of-DC_FPU_-BEGIN-END-with-PREEMPT_RT/20260805-170330
base:   next-20260804
patch link:    https://lore.kernel.org/r/20260801071724.12998-1-spasswolf%40web.de
patch subject: [PATCH] drm/amd/display: fix usage of DC_FPU_{BEGIN,END} with PREEMPT_RT
config: alpha-allyesconfig (https://download.01.org/0day-ci/archive/20260806/202608061233.eufnR5Qm-lkp@intel.com/config)
compiler: alpha-linux-gcc (GCC) 16.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260806/202608061233.eufnR5Qm-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202608061233.eufnR5Qm-lkp@intel.com/

All errors (new ones prefixed by >>):

   drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_surface.c: In function 'dc_create_plane_state':
>> drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_surface.c:89:9: error: implicit declaration of function 'DC_RUN_WITH_PREEMPTION_ENABLED' [-Wimplicit-function-declaration]
      89 |         DC_RUN_WITH_PREEMPTION_ENABLED(plane_state = kvzalloc_obj(*plane_state, GFP_ATOMIC));
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


vim +/DC_RUN_WITH_PREEMPTION_ENABLED +89 drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_surface.c

    82	
    83	/*******************************************************************************
    84	 * Public functions
    85	 ******************************************************************************/
    86	struct dc_plane_state *dc_create_plane_state(const struct dc *dc)
    87	{
    88		struct dc_plane_state *plane_state;
  > 89		DC_RUN_WITH_PREEMPTION_ENABLED(plane_state = kvzalloc_obj(*plane_state, GFP_ATOMIC));
    90	
    91		if (NULL == plane_state)
    92			return NULL;
    93	
    94		kref_init(&plane_state->refcount);
    95		dc_plane_construct(dc->ctx, plane_state);
    96	
    97		return plane_state;
    98	}
    99	

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

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

[Bert Karwatzki]

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@web.de/
Signed-off-by: Bert Karwatzki <spasswolf@web.de>
---
 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

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@web.de/
> Signed-off-by: Bert Karwatzki <spasswolf@web.de>
> ---
>  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>