[PATCH 03/10] dma-buf: add dma_fence_array_recycle

[Chris Wilson]

Quoting Christian König (2019-08-21 13:31:40)
> Try to recycle an dma_fence_array object by dropping the last
> reference to it without freeing it.
> 
> Signed-off-by: Christian König <christian.koenig at amd.com>
> ---
>  drivers/dma-buf/dma-fence-array.c | 27 +++++++++++++++++++++++++++
>  include/linux/dma-fence-array.h   |  1 +
>  2 files changed, 28 insertions(+)
> 
> diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c
> index e82f30551aa1..314cf0e881d9 100644
> --- a/drivers/dma-buf/dma-fence-array.c
> +++ b/drivers/dma-buf/dma-fence-array.c
> @@ -188,6 +188,33 @@ void dma_fence_array_init(struct dma_fence_array *array, u64 context,
>  }
>  EXPORT_SYMBOL(dma_fence_array_init);
>  
> +/**
> + * dma_fence_array_reuse - dummy for dma_fence_array_recycle
> + */
> +static void dma_fence_array_reuse(struct kref *kref)
> +{
> +       struct dma_fence_array *array = container_of(kref, typeof(*array),
> +                                                    base.refcount);
> +
> +       WARN_ON_ONCE(!list_empty(&array->base.cb_list));

[   77.584694] WARNING: CPU: 3 PID: 627 at drivers/dma-buf/dma-fence-array.c:199 dma_fence_array_recycle+0x1d/0x20
[   77.584702] Modules linked in: nls_ascii nls_cp437 vfat fat crct10dif_pclmul i915 crc32_pclmul crc32c_intel aesni_intel aes_x86_64 glue_helper crypto_simd cryptd intel_cstate intel_gtt drm_kms_helper intel_uncore intel_rapl_perf ahci i2c_i801 libahci efivars video button efivarfs
[   77.584716] CPU: 3 PID: 627 Comm: gem_busy Tainted: G     U            5.3.0-rc5+ #72
[   77.584719] Hardware name: Intel Corporation NUC7i5BNK/NUC7i5BNB, BIOS BNKBL357.86A.0052.2017.0918.1346 09/18/2017
[   77.584723] RIP: 0010:dma_fence_array_recycle+0x1d/0x20
[   77.584726] Code: 5d c3 5b 5d e9 54 f5 ff ff 0f 1f 40 00 f0 ff 4f 38 0f 88 d3 85 14 00 0f 94 c0 74 01 c3 48 8b 57 10 48 83 c7 10 48 39 d7 74 f2 <0f> 0b c3 48 c7 c0 62 88 be 81 c3 0f 1f 84 00 00 00 00 00 48 c7 c0
[   77.584730] RSP: 0018:ffffc900001c3c78 EFLAGS: 00010292
[   77.584733] RAX: 0000000000000001 RBX: ffff88885ac14b40 RCX: cccccccccccccccd
[   77.584735] RDX: 00000012105b0a77 RSI: 0000000000000000 RDI: ffff88885ac14b50
[   77.584737] RBP: 0000000000000000 R08: 0000000000000004 R09: 000000000001de00
[   77.584740] R10: 00000030f5224012 R11: 00000000000002df R12: ffff88885b58aff0
[   77.584742] R13: 0000000000000000 R14: 0000000000000000 R15: ffff88885748e100
[   77.584745] FS:  00007f1cd47b19c0(0000) GS:ffff88885eb80000(0000) knlGS:0000000000000000
[   77.584748] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   77.584750] CR2: 00007f1cd6719000 CR3: 000000085ac5b002 CR4: 00000000001606e0
[   77.584753] Call Trace:
[   77.584758]  dma_resv_fences_assign.isra.7+0x8d/0x220
[   77.584761]  dma_resv_prune_fences+0xba/0xc0
[   77.584796]  i915_gem_object_wait_reservation+0x226/0x240 [i915]
[   77.584827]  i915_gem_object_wait+0x23/0x40 [i915]
[   77.584854]  i915_gem_set_domain_ioctl+0xbf/0x240 [i915]

If we signal the fence-array, the cb_list is replaced by the timestamp
and is no longer considered empty.
-Chris