Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> Take the obj->vma.lock to prevent modifications to the list as we
> iterate, to avoid the dreaded the NULL pointer.
>
> <1>[ 347.820823] BUG: kernel NULL pointer dereference, address: 0000000000000150
> <1>[ 347.820856] #PF: supervisor read access in kernel mode
> <1>[ 347.820874] #PF: error_code(0x0000) - not-present page
> <6>[ 347.820892] PGD 0 P4D 0
> <4>[ 347.820908] Oops: 0000 [#1] PREEMPT SMP NOPTI
> <4>[ 347.820926] CPU: 3 PID: 1303 Comm: gem_persistent_ Tainted: G U 5.4.0-rc7-CI-CI_DRM_7352+ #1
> <4>[ 347.820956] Hardware name: /NUC6CAYB, BIOS AYAPLCEL.86A.0049.2018.0508.1356 05/08/2018
> <4>[ 347.821132] RIP: 0010:i915_gem_object_flush_write_domain+0xd9/0x1d0 [i915]
> <4>[ 347.821157] Code: 0f 84 e9 00 00 00 48 8b 80 e0 fd ff ff f6 c4 40 75 11 e9 ed 00 00 00 48 8b 80 e0 fd ff ff f6 c4 40 74 26 48 8b 83 b0 00 00 00 <48> 8b b8 50 01 00 00 e8 fb 20 fb ff 48 8b 83 30 03 00 00 49 39 c4
> <4>[ 347.821210] RSP: 0018:ffffc90000a1f8f8 EFLAGS: 00010202
> <4>[ 347.821229] RAX: 0000000000000000 RBX: ffffc900008479a0 RCX: 0000000000000018
> <4>[ 347.821252] RDX: 0000000000000000 RSI: 000000000000000d RDI: ffff888275a090b0
> <4>[ 347.821274] RBP: ffff8882673c8040 R08: ffff88825991b8d0 R09: 0000000000000000
> <4>[ 347.821297] R10: 0000000000000000 R11: 0000000000000000 R12: ffff8882673c8280
> <4>[ 347.821319] R13: ffff8882673c8368 R14: 0000000000000000 R15: ffff888266a54000
> <4>[ 347.821343] FS: 00007f75865f4240(0000) GS:ffff888277b80000(0000) knlGS:0000000000000000
> <4>[ 347.821368] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> <4>[ 347.821389] CR2: 0000000000000150 CR3: 000000025aee0000 CR4: 00000000003406e0
> <4>[ 347.821411] Call Trace:
> <4>[ 347.821555] i915_gem_object_prepare_read+0xea/0x2a0 [i915]
> <4>[ 347.821706] intel_engine_cmd_parser+0x5ce/0xe90 [i915]
> <4>[ 347.821834] ? __i915_sw_fence_complete+0x1a0/0x250 [i915]
> <4>[ 347.821990] i915_gem_do_execbuffer+0xb4c/0x2550 [i915]
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/gem/i915_gem_object.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c
> index 63bd3ff84f5e..458945e1823e 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
> @@ -279,10 +279,12 @@ i915_gem_object_flush_write_domain(struct drm_i915_gem_object *obj,
>
> switch (obj->write_domain) {
> case I915_GEM_DOMAIN_GTT:
> + spin_lock(&obj->vma.lock);
> for_each_ggtt_vma(vma, obj) {
> if (i915_vma_unset_ggtt_write(vma))
> intel_gt_flush_ggtt_writes(vma->vm->gt);
> }
> + spin_unlock(&obj->vma.lock);
>
> intel_frontbuffer_flush(obj->frontbuffer, ORIGIN_CPU);
> break;
> --
> 2.24.0
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