Re: [Intel-gfx] [RFC PATCH 1/4] drm/i915: Drop user contexts on driver remove

[Michał Winiarski <michal@hardline.pl>]

Quoting Janusz Krzysztofik (2020-05-18 20:17:17)
> Contexts associated with open device file descriptors together with
> their assigned address spaces are now closed on device file close.  On
> address space closure its associated DMA mappings are revoked.  If the
> device is removed while being open, subsequent attempts to revoke
> those mappings while closing the device file descriptor may may be
> judged by intel-iommu code as a bug and result in kernel panic.
> 
> Since user contexts become useless after the device is no longer
> available, drop them on device removal.
> 
> <4> [36.900985] ------------[ cut here ]------------
> <2> [36.901005] kernel BUG at drivers/iommu/intel-iommu.c:3717!
> <4> [36.901105] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
> <4> [36.901117] CPU: 0 PID: 39 Comm: kworker/u8:1 Tainted: G     U  W         5.7.0-rc5-CI-CI_DRM_8485+ #1
> <4> [36.901133] Hardware name: Intel Corporation Elkhart Lake Embedded Platform/ElkhartLake LPDDR4x T3 CRB, BIOS EHLSFWI1.R00.1484.A00.1911290833 11/29/2019
> <4> [36.901250] Workqueue: i915 __i915_vm_release [i915]
> <4> [36.901264] RIP: 0010:intel_unmap+0x1f5/0x230
> <4> [36.901274] Code: 01 e8 9f bc a9 ff 85 c0 74 09 80 3d df 60 09 01 00 74 19 65 ff 0d 13 12 97 7e 0f 85 fc fe ff ff e8 82 b0 95 ff e9 f2 fe ff ff <0f> 0b e8 d4 bd a9 ff 85 c0 75 de 48 c7 c2 10 84 2c 82 be 54 00 00
> <4> [36.901302] RSP: 0018:ffffc900001ebdc0 EFLAGS: 00010246
> <4> [36.901313] RAX: 0000000000000000 RBX: ffff8882561dd000 RCX: 0000000000000000
> <4> [36.901324] RDX: 0000000000001000 RSI: 00000000ffd9c000 RDI: ffff888274c94000
> <4> [36.901336] RBP: ffff888274c940b0 R08: 0000000000000000 R09: 0000000000000001
> <4> [36.901348] R10: 000000000a25d812 R11: 00000000112af2d4 R12: ffff888252c70200
> <4> [36.901360] R13: 00000000ffd9c000 R14: 0000000000001000 R15: ffff8882561dd010
> <4> [36.901372] FS:  0000000000000000(0000) GS:ffff888278000000(0000) knlGS:0000000000000000
> <4> [36.901386] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> <4> [36.901396] CR2: 00007f06def54950 CR3: 0000000255844000 CR4: 0000000000340ef0
> <4> [36.901408] Call Trace:
> <4> [36.901418]  ? process_one_work+0x1de/0x600
> <4> [36.901494]  cleanup_page_dma+0x37/0x70 [i915]
> <4> [36.901573]  free_pd+0x9/0x20 [i915]
> <4> [36.901644]  gen8_ppgtt_cleanup+0x59/0xc0 [i915]
> <4> [36.901721]  __i915_vm_release+0x14/0x30 [i915]
> <4> [36.901733]  process_one_work+0x268/0x600
> <4> [36.901744]  ? __schedule+0x307/0x8d0
> <4> [36.901756]  worker_thread+0x37/0x380
> <4> [36.901766]  ? process_one_work+0x600/0x600
> <4> [36.901775]  kthread+0x140/0x160
> <4> [36.901783]  ? kthread_park+0x80/0x80
> <4> [36.901792]  ret_from_fork+0x24/0x50
> <4> [36.901804] Modules linked in: mei_hdcp i915 x86_pkg_temp_thermal coretemp crct10dif_pclmul crc32_pclmul ghash_clmulni_intel ax88179_178a usbnet mii mei_me mei prime_numbers intel_lpss_pci
> <4> [36.901857] ---[ end trace 52d1b4d81f8d1ea7 ]---
> 
> Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_context.c | 38 +++++++++++++++++++++
>  drivers/gpu/drm/i915/gem/i915_gem_context.h |  1 +
>  drivers/gpu/drm/i915/i915_gem.c             |  2 ++
>  3 files changed, 41 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> index 900ea8b7fc8f..0096a69fbfd3 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> @@ -927,6 +927,44 @@ void i915_gem_driver_release__contexts(struct drm_i915_private *i915)
>         rcu_barrier(); /* and flush the left over RCU frees */
>  }
>  
> +void i915_gem_driver_remove__contexts(struct drm_i915_private *i915)
> +{
> +       struct i915_gem_context *ctx, *cn;
> +
> +       list_for_each_entry_safe(ctx, cn, &i915->gem.contexts.list, link) {

You're not removing ctx from gem.contexts.list inside this loop.

> +               struct drm_i915_file_private *file_priv = ctx->file_priv;
> +               struct i915_gem_context *entry;
> +               unsigned long int id;
> +
> +               if (i915_gem_context_is_closed(ctx) || IS_ERR(file_priv))
> +                       continue;
> +
> +               xa_for_each(&file_priv->context_xa, id, entry) {

We're iterating over contexts?
I thought we were already doing that by going over i915->gem.contexts.list.

> +                       struct i915_address_space *vm;
> +                       unsigned long int idx;
> +
> +                       if (entry != ctx)
> +                               continue;
> +
> +                       xa_erase(&file_priv->context_xa, id);
> +
> +                       if (id)
> +                               break;

Ok... So we're exiting early for !default contexts?

> +
> +                       xa_for_each(&file_priv->vm_xa, idx, vm) {
> +                               xa_erase(&file_priv->vm_xa, idx);
> +                               i915_vm_put(vm);
> +                       }

And for each vm as yet another inner loop?
Why? After the first round of going over contexts this is going to be empty.

> +
> +                       break;

Ah... But there won't be another round...

Yeah, the intent behind those loops is not clear to me.

Can this all be expressed as (note: pseudocode):

/* for all fds */
list_for_each(&dev.filelist) {
	/* for each contexts registered to this file */
	xa_for_each(&file_priv->context_xa) {
		/* drop ctx */
	}
	/* for each VM registered to this file */
	xa_for_each(&file_priv->vm_xa) {
		/* drop VM */
	}
}

Or am I missing something important here?

-Michał

> +               }
> +
> +               context_close(ctx);
> +       }
> +
> +       i915_gem_driver_release__contexts(i915);
> +}
> +
>  static int gem_context_register(struct i915_gem_context *ctx,
>                                 struct drm_i915_file_private *fpriv,
>                                 u32 *id)
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.h b/drivers/gpu/drm/i915/gem/i915_gem_context.h
> index 3702b2fb27ab..62808bea9239 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.h
> @@ -110,6 +110,7 @@ i915_gem_context_clear_user_engines(struct i915_gem_context *ctx)
>  
>  /* i915_gem_context.c */
>  void i915_gem_init__contexts(struct drm_i915_private *i915);
> +void i915_gem_driver_remove__contexts(struct drm_i915_private *i915);
>  void i915_gem_driver_release__contexts(struct drm_i915_private *i915);
>  
>  int i915_gem_context_open(struct drm_i915_private *i915,
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 0cbcb9f54e7d..87d3c4f5b6c6 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1189,6 +1189,8 @@ void i915_gem_driver_remove(struct drm_i915_private *dev_priv)
>         /* Flush any outstanding unpin_work. */
>         i915_gem_drain_workqueue(dev_priv);
>  
> +       i915_gem_driver_remove__contexts(dev_priv);
> +
>         i915_gem_drain_freed_objects(dev_priv);
>  }
>  
> -- 
> 2.21.1
> 
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