Messages in this thread Patch in this message |  | | From | Mikhail Gavrilov <> | | Subject | [PATCH] drm/amd/display: Wrap DCN32 phantom-plane allocation in DC_RUN_WITH_PREEMPTION_ENABLED | | Date | Tue, 5 May 2026 01:19:05 +0500 |
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dcn32_validate_bandwidth() wraps dcn32_internal_validate_bw() with DC_FP_START()/DC_FP_END(). On x86 non-RT, DC_FP_START expands into kernel_fpu_begin() which takes fpregs_lock(), i.e. local_bh_disable(). Allocations done inside this region must therefore not sleep.
The legacy DML1 path through dcn32_full_validate_bw_helper() -> dcn32_add_phantom_pipes() -> dcn32_enable_phantom_plane() unconditionally calls dc_state_create_phantom_plane() -> dc_create_plane_state(), which performs kvzalloc(sizeof(struct dc_plane_state)). On a recent kernel sizeof(struct dc_plane_state) is 343736 bytes (335 KiB), well above the PAGE_ALLOC_COSTLY_ORDER threshold, so __kvmalloc_node() takes the vmalloc path. __get_vm_area_node() then trips its BUG_ON(in_interrupt()) because SOFTIRQ_DISABLE_OFFSET is set in preempt_count:
kernel BUG at mm/vmalloc.c:3206! RIP: __get_vm_area_node+0x257/0x2d0 Workqueue: events_unbound commit_work Call Trace: __vmalloc_node_range_noprof+0x22b/0x570 __kvmalloc_node_noprof+0x3d0/0xb40 dc_create_plane_state+0x35/0x290 [amdgpu] dc_state_create_phantom_plane+0x1a/0x120 [amdgpu] dcn32_enable_phantom_plane+0x101/0x780 [amdgpu] dcn32_add_phantom_pipes+0x47/0x460 [amdgpu] dcn32_full_validate_bw_helper.constprop.0+0xa46/0x1d70 [amdgpu] dcn32_internal_validate_bw+0x49c/0x1600 [amdgpu] dml1_validate+0x20f/0x800 [amdgpu] dcn32_validate_bandwidth+0x317/0x540 [amdgpu] dc_validate_with_context+0xd34/0x1d30 [amdgpu] dc_commit_streams+0x7ca/0x1810 [amdgpu] amdgpu_dm_commit_streams+0xfd4/0x1e60 [amdgpu] amdgpu_dm_atomic_commit_tail+0x29e/0x3520 [amdgpu] commit_tail+0x204/0x4b0 process_one_work+0x8fd/0x16a0
Per-CPU __preempt_count on the crashing CPU at panic time was 0x202: SOFTIRQ_DISABLE_OFFSET (0x200) from fpregs_lock() plus two preempt holds from dc_fpu_begin() and kernel_fpu_begin().
The DML2 paths already wrap their large vzalloc()s in DC_RUN_WITH_PREEMPTION_ENABLED() to handle this case (see drivers/gpu/drm/amd/display/dc/dml2_0/dml21/dml21_wrapper.c:26 and drivers/gpu/drm/amd/display/dc/dml2_0/dml2_wrapper.c:24). Apply the same guard to the DML1 phantom-plane allocation in dcn32_enable_phantom_plane().
This is a separate class of issue from "drm/amd/display: Fix unsafe uses of kernel mode FPU" by Ard Biesheuvel, which addressed callers entering DC FP compilation units without DC_FP_START. The bug fixed here is the inverse: a sleeping allocator invoked from within an active DC_FP_START region.
Reproducer (RX 7900 XTX, single 4K HDMI display, DCN 3.2): launch any workload that produces rapid atomic modeset commits. The most reliable trigger observed is launching Rise of the Tomb Raider via Proton and repeatedly pressing the Super key during the level loading screen; crash occurs within ~4 minutes uptime. Random crashes are also observed during routine fullscreen toggles (image viewers, chat applications).
Hardware verified clean: memtest86+ 4 passes, stressapptest -W -m 32 4 hours, both pass with 0 errors. KASAN active, no reports under load.
Fixes: 235c67634230 ("drm/amd/display: add DCN32/321 specific files for Display Core") Cc: stable@vger.kernel.org # v6.0+ Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com> --- .../drm/amd/display/dc/resource/dcn32/dcn32_resource.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/amd/display/dc/resource/dcn32/dcn32_resource.c b/drivers/gpu/drm/amd/display/dc/resource/dcn32/dcn32_resource.c index 82f81b586986..3751f7a94a05 100644 --- a/drivers/gpu/drm/amd/display/dc/resource/dcn32/dcn32_resource.c +++ b/drivers/gpu/drm/amd/display/dc/resource/dcn32/dcn32_resource.c @@ -92,9 +92,14 @@ #include "dml/dcn32/dcn32_fpu.h" #include "dc_state_priv.h" +#include "dc_fpu.h" #include "dml2_0/dml2_wrapper.h" +#if !defined(DC_RUN_WITH_PREEMPTION_ENABLED) +#define DC_RUN_WITH_PREEMPTION_ENABLED(code) code +#endif + #define DC_LOGGER_INIT(logger) enum dcn32_clk_src_array_id { @@ -1684,7 +1689,8 @@ static void dcn32_enable_phantom_plane(struct dc *dc, if (curr_pipe->top_pipe && curr_pipe->top_pipe->plane_state == curr_pipe->plane_state) phantom_plane = prev_phantom_plane; else - phantom_plane = dc_state_create_phantom_plane(dc, context, curr_pipe->plane_state); + DC_RUN_WITH_PREEMPTION_ENABLED(phantom_plane = + dc_state_create_phantom_plane(dc, context, curr_pipe->plane_state)); if (!phantom_plane) continue; -- 2.54.0
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