On Tue, May 12, 2020 at 6:20 PM Daniel Vetter <daniel.vetter@xxxxxxxx> wrote: > > On Tue, May 12, 2020 at 5:56 PM Christian König > <christian.koenig@xxxxxxx> wrote: > > > > Hui what? Of hand that doesn't looks correct to me. > > It's not GFP_ATOMIC, it's just that GFP_ATOMIC is the only shotgun we > have to avoid direct reclaim. And direct reclaim might need to call > into your mmu notifier, which might need to wait on a fence, which is > never going to happen because your scheduler is stuck. > > Note that all the explanations for the deadlocks and stuff I'm trying > to hunt here are in the other patches, the driver ones are more > informational, so I left these here rather bare-bones to shut up > lockdep so I can get through the entire driver and all major areas > (scheduler, reset, modeset code). > > Now you can do something like GFP_NOFS, but the only reasons that > works is because the direct reclaim annotations > (fs_reclaim_acquire/release) only validates against __GFP_FS, and not > against any of the other flags. We should probably add some lockdep > annotations so that __GFP_RECLAIM is annotated against the > __mmu_notifier_invalidate_range_start_map lockdep map I've recently > added for mmu notifiers. End result (assuming I'm not mixing anything > up here, this is all rather tricky stuff): GFP_ATOMIC is the only kind > of memory allocation you can do. > > > Why the heck should this be an atomic context? If that's correct > > allocating memory is the least of the problems we have. > > It's not about atomic, it's !__GFP_RECLAIM. Which more or less is > GFP_ATOMIC. Correct fix is probably GFP_ATOMIC + a mempool for the > scheduler fixes so that if you can't allocate them for some reason, > you at least know that your scheduler should eventually retire retire > some of them, which you can then pick up from the mempool to guarantee > forward progress. > > But I really didn't dig into details of the code, this was just a quick hack. > > So sleeping and taking all kinds of locks (but not all, e.g. > dma_resv_lock and drm_modeset_lock are no-go) is still totally ok. > Just think > > #define GFP_NO_DIRECT_RECLAIM GFP_ATOMIC Maybe slightly different take that's easier to understand: You've already made the observation that anything holding adev->notifier_lock isn't allowed to allocate memory (well GFP_ATOMIC is ok, like here). Only thing I'm adding is that the situation is a lot worse. Plus the lockdep annotations to help us catch these issues. -Daniel > Cheers, Daniel > > > > > Regards, > > Christian. > > > > Am 12.05.20 um 10:59 schrieb Daniel Vetter: > > > My dma-fence lockdep annotations caught an inversion because we > > > allocate memory where we really shouldn't: > > > > > > kmem_cache_alloc+0x2b/0x6d0 > > > amdgpu_fence_emit+0x30/0x330 [amdgpu] > > > amdgpu_ib_schedule+0x306/0x550 [amdgpu] > > > amdgpu_job_run+0x10f/0x260 [amdgpu] > > > drm_sched_main+0x1b9/0x490 [gpu_sched] > > > kthread+0x12e/0x150 > > > > > > Trouble right now is that lockdep only validates against GFP_FS, which > > > would be good enough for shrinkers. But for mmu_notifiers we actually > > > need !GFP_ATOMIC, since they can be called from any page laundering, > > > even if GFP_NOFS or GFP_NOIO are set. > > > > > > I guess we should improve the lockdep annotations for > > > fs_reclaim_acquire/release. > > > > > > Ofc real fix is to properly preallocate this fence and stuff it into > > > the amdgpu job structure. But GFP_ATOMIC gets the lockdep splat out of > > > the way. > > > > > > v2: Two more allocations in scheduler paths. > > > > > > Frist one: > > > > > > __kmalloc+0x58/0x720 > > > amdgpu_vmid_grab+0x100/0xca0 [amdgpu] > > > amdgpu_job_dependency+0xf9/0x120 [amdgpu] > > > drm_sched_entity_pop_job+0x3f/0x440 [gpu_sched] > > > drm_sched_main+0xf9/0x490 [gpu_sched] > > > > > > Second one: > > > > > > kmem_cache_alloc+0x2b/0x6d0 > > > amdgpu_sync_fence+0x7e/0x110 [amdgpu] > > > amdgpu_vmid_grab+0x86b/0xca0 [amdgpu] > > > amdgpu_job_dependency+0xf9/0x120 [amdgpu] > > > drm_sched_entity_pop_job+0x3f/0x440 [gpu_sched] > > > drm_sched_main+0xf9/0x490 [gpu_sched] > > > > > > Cc: linux-media@xxxxxxxxxxxxxxx > > > Cc: linaro-mm-sig@xxxxxxxxxxxxxxxx > > > Cc: linux-rdma@xxxxxxxxxxxxxxx > > > Cc: amd-gfx@xxxxxxxxxxxxxxxxxxxxx > > > Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx > > > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > > Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx> > > > Cc: Christian König <christian.koenig@xxxxxxx> > > > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> > > > --- > > > drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c | 2 +- > > > drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c | 2 +- > > > drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c | 2 +- > > > 3 files changed, 3 insertions(+), 3 deletions(-) > > > > > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c > > > index d878fe7fee51..055b47241bb1 100644 > > > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c > > > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c > > > @@ -143,7 +143,7 @@ int amdgpu_fence_emit(struct amdgpu_ring *ring, struct dma_fence **f, > > > uint32_t seq; > > > int r; > > > > > > - fence = kmem_cache_alloc(amdgpu_fence_slab, GFP_KERNEL); > > > + fence = kmem_cache_alloc(amdgpu_fence_slab, GFP_ATOMIC); > > > if (fence == NULL) > > > return -ENOMEM; > > > > > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c > > > index fe92dcd94d4a..fdcd6659f5ad 100644 > > > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c > > > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c > > > @@ -208,7 +208,7 @@ static int amdgpu_vmid_grab_idle(struct amdgpu_vm *vm, > > > if (ring->vmid_wait && !dma_fence_is_signaled(ring->vmid_wait)) > > > return amdgpu_sync_fence(sync, ring->vmid_wait, false); > > > > > > - fences = kmalloc_array(sizeof(void *), id_mgr->num_ids, GFP_KERNEL); > > > + fences = kmalloc_array(sizeof(void *), id_mgr->num_ids, GFP_ATOMIC); > > > if (!fences) > > > return -ENOMEM; > > > > > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c > > > index b87ca171986a..330476cc0c86 100644 > > > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c > > > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c > > > @@ -168,7 +168,7 @@ int amdgpu_sync_fence(struct amdgpu_sync *sync, struct dma_fence *f, > > > if (amdgpu_sync_add_later(sync, f, explicit)) > > > return 0; > > > > > > - e = kmem_cache_alloc(amdgpu_sync_slab, GFP_KERNEL); > > > + e = kmem_cache_alloc(amdgpu_sync_slab, GFP_ATOMIC); > > > if (!e) > > > return -ENOMEM; > > > > > > > > -- > Daniel Vetter > Software Engineer, Intel Corporation > +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch
