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Thu, 21 May 2026 03:43:45 -0700 (PDT) From: Mikhail Gavrilov To: amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Cc: Alex Deucher , =?UTF-8?q?Christian=20K=C3=B6nig?= , David Airlie , Simona Vetter , Pierre-Eric Pelloux-Prayer , Sumit Semwal , linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, Mikhail Gavrilov Subject: [PATCH v4 2/2] drm/amdgpu: fix recursive ww_mutex acquire in amdgpu_devcoredump_format Date: Thu, 21 May 2026 15:43:33 +0500 Message-ID: <20260521104335.28978-3-mikhail.v.gavrilov@gmail.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260521104335.28978-1-mikhail.v.gavrilov@gmail.com> References: <20260520151741.50575-1-mikhail.v.gavrilov@gmail.com> <20260521104335.28978-1-mikhail.v.gavrilov@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When dumping IB contents from a hung job, amdgpu_devcoredump_format() acquired the VM root PD's reservation via amdgpu_vm_lock_by_pasid() and then, for each IB, called amdgpu_bo_reserve() on the BO backing the IB. Both reservations are reservation_ww_class_mutex objects and neither used a ww_acquire_ctx, which trips lockdep: WARNING: possible recursive locking detected -------------------------------------------- kworker/u128:0 is trying to acquire lock: ffff88838b16e1f0 (reservation_ww_class_mutex){+.+.}-{4:4}, at: amdgpu_devcoredump_format+0x1594/0x23f0 [amdgpu] but task is already holding lock: ffff8882f82681f0 (reservation_ww_class_mutex){+.+.}-{4:4}, at: amdgpu_devcoredump_format+0x1594/0x23f0 [amdgpu] Possible unsafe locking scenario: CPU0 ---- lock(reservation_ww_class_mutex); lock(reservation_ww_class_mutex); *** DEADLOCK *** May be due to missing lock nesting notation Workqueue: events_unbound amdgpu_devcoredump_deferred_work [amdgpu] Call Trace: __ww_mutex_lock.constprop.0 ww_mutex_lock amdgpu_bo_reserve amdgpu_devcoredump_format+0x1594 [amdgpu] amdgpu_devcoredump_deferred_work+0xea [amdgpu] The two reservations are on different BOs in the captured trace, so the splat is a lockdep-correctness warning, not an observed deadlock. It becomes a real self-deadlock whenever the IB BO shares its dma_resv with the root PD (the always-valid case, see amdgpu_vm_is_bo_always_valid()): amdgpu_bo_reserve(abo) re-acquires the same ww_mutex without a ticket and blocks forever. With amdgpu.gpu_recovery=0 the timeout handler refires every ~2 s and each invocation produces this splat, drowning the kernel ring buffer. Now that amdgpu_vm_lock_by_pasid() takes a drm_exec context, lock the root PD and every IB BO together in a single drm_exec ticket. DRM_EXEC_IGNORE_DUPLICATES handles IB BOs that share a dma_resv (e.g. always-valid BOs, or two IBs backed by the same BO). Every lock is now a top-level acquire under one ww_acquire_ctx, so the recursive ww_mutex condition is gone, and the per-IB amdgpu_bo_reserve()/amdgpu_bo_unref() dance -- including a BO refcount leak on the amdgpu_bo_reserve() failure path -- is removed. Reproducer (~150 LoC libdrm_amdgpu): submit a single GFX IB containing PACKET3_INDIRECT_BUFFER chained at GPU VA 0 and wait for the fence. The TDR fires within ~10 s and the deferred coredump worker produces the splat above on every invocation; with this change applied the splat is gone. Fixes: 7b15fc2d1f1a ("drm/amdgpu: dump job ibs in the devcoredump") Suggested-by: Christian König Signed-off-by: Mikhail Gavrilov --- .../gpu/drm/amd/amdgpu/amdgpu_dev_coredump.c | 105 ++++++++++++------ 1 file changed, 71 insertions(+), 34 deletions(-) diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dev_coredump.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_dev_coredump.c index d386bc775d03..456ea9911d48 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dev_coredump.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dev_coredump.c @@ -24,6 +24,7 @@ #include #include +#include #include "amdgpu_dev_coredump.h" #include "atom.h" @@ -214,13 +215,9 @@ amdgpu_devcoredump_format(char *buffer, size_t count, struct amdgpu_coredump_inf struct drm_printer p; struct drm_print_iterator iter; struct amdgpu_vm_fault_info *fault_info; - struct amdgpu_bo_va_mapping *mapping; struct amdgpu_ip_block *ip_block; struct amdgpu_res_cursor cursor; - struct amdgpu_bo *abo, *root; - uint64_t va_start, offset; struct amdgpu_ring *ring; - struct amdgpu_vm *vm; u32 *ib_content; uint8_t *kptr; int ver, i, j, r; @@ -343,43 +340,84 @@ amdgpu_devcoredump_format(char *buffer, size_t count, struct amdgpu_coredump_inf drm_printf(&p, "VRAM is lost due to GPU reset!\n"); if (coredump->num_ibs) { - /* Don't try to lookup the VM or map the BOs when calculating the - * size required to store the devcoredump. + struct amdgpu_bo_va_mapping *mapping; + struct amdgpu_bo *abo; + struct drm_exec exec; + struct amdgpu_vm *vm; + u64 va_start, offset; + bool locked = false; + + /* + * Lock the VM root PD and every IB BO together in a single + * drm_exec ticket. Reserving the IB BOs one by one while the + * root PD is held would be a recursive reservation_ww_class_mutex + * acquire without a ww_acquire_ctx, which trips lockdep and + * self-deadlocks for IB BOs that share their dma_resv with the + * root PD (always-valid BOs). + * + * Skip locking entirely on the sizing pass: it does not write + * IB content, so the size estimate doesn't depend on whether + * the BOs are reachable. */ - if (sizing_pass) - vm = NULL; - else - vm = amdgpu_vm_lock_by_pasid(adev, &root, coredump->pasid); + if (!sizing_pass) { + drm_exec_init(&exec, DRM_EXEC_IGNORE_DUPLICATES, + 1 + coredump->num_ibs); + drm_exec_until_all_locked(&exec) { + vm = amdgpu_vm_lock_by_pasid(adev, coredump->pasid, + &exec); + drm_exec_retry_on_contention(&exec); + if (!vm) + break; + + for (int i = 0; i < coredump->num_ibs; i++) { + u64 pfn; + + va_start = coredump->ibs[i].gpu_addr & + AMDGPU_GMC_HOLE_MASK; + pfn = va_start / AMDGPU_GPU_PAGE_SIZE; + mapping = amdgpu_vm_bo_lookup_mapping(vm, pfn); + if (!mapping) + continue; + + abo = mapping->bo_va->base.bo; + r = drm_exec_lock_obj(&exec, &abo->tbo.base); + drm_exec_retry_on_contention(&exec); + if (r) + break; + } + if (r) + break; + } + if (vm && !r) + locked = true; + else + drm_exec_fini(&exec); + } + + for (int i = 0; i < coredump->num_ibs; i++) { + bool emit_content = sizing_pass; - for (int i = 0; i < coredump->num_ibs && (sizing_pass || vm); i++) { ib_content = kvmalloc_array(coredump->ibs[i].ib_size_dw, 4, GFP_KERNEL); if (!ib_content) continue; - /* vm=NULL can only happen when 'sizing_pass' is true. Skip to the - * drm_printf() calls (ib_content doesn't need to be initialized - * as its content won't be written anywhere). - */ - if (!vm) + if (!locked) goto output_ib_content; va_start = coredump->ibs[i].gpu_addr & AMDGPU_GMC_HOLE_MASK; mapping = amdgpu_vm_bo_lookup_mapping(vm, va_start / AMDGPU_GPU_PAGE_SIZE); if (!mapping) - goto free_ib_content; + goto output_ib_content; - offset = va_start - (mapping->start * AMDGPU_GPU_PAGE_SIZE); - abo = amdgpu_bo_ref(mapping->bo_va->base.bo); - r = amdgpu_bo_reserve(abo, false); - if (r) - goto free_ib_content; + abo = mapping->bo_va->base.bo; + offset = va_start - mapping->start * AMDGPU_GPU_PAGE_SIZE; if (abo->flags & AMDGPU_GEM_CREATE_NO_CPU_ACCESS) { off = 0; if (abo->tbo.resource->mem_type != TTM_PL_VRAM) - goto unreserve_abo; + goto output_ib_content; amdgpu_res_first(abo->tbo.resource, offset, coredump->ibs[i].ib_size_dw * 4, @@ -391,12 +429,13 @@ amdgpu_devcoredump_format(char *buffer, size_t count, struct amdgpu_coredump_inf off += cursor.size; amdgpu_res_next(&cursor, cursor.size); } + emit_content = true; } else { r = ttm_bo_kmap(&abo->tbo, 0, PFN_UP(abo->tbo.base.size), &abo->kmap); if (r) - goto unreserve_abo; + goto output_ib_content; kptr = amdgpu_bo_kptr(abo); kptr += offset; @@ -404,23 +443,21 @@ amdgpu_devcoredump_format(char *buffer, size_t count, struct amdgpu_coredump_inf coredump->ibs[i].ib_size_dw * 4); amdgpu_bo_kunmap(abo); + emit_content = true; } output_ib_content: drm_printf(&p, "\nIB #%d 0x%llx %d dw\n", i, coredump->ibs[i].gpu_addr, coredump->ibs[i].ib_size_dw); - for (int j = 0; j < coredump->ibs[i].ib_size_dw; j++) - drm_printf(&p, "0x%08x\n", ib_content[j]); -unreserve_abo: - if (vm) - amdgpu_bo_unreserve(abo); -free_ib_content: + if (emit_content) { + for (int j = 0; j < coredump->ibs[i].ib_size_dw; j++) + drm_printf(&p, "0x%08x\n", ib_content[j]); + } kvfree(ib_content); } - if (vm) { - amdgpu_bo_unreserve(root); - amdgpu_bo_unref(&root); - } + + if (locked) + drm_exec_fini(&exec); } return count - iter.remain; -- 2.54.0