[Intel-gfx] [PATCH] dma-resv: Fix dma_resv_get_fences and dma_resv_copy_fences after conversion

[Tvrtko Ursulin]

On 08/10/2021 13:19, Christian König wrote:
> Am 08.10.21 um 12:49 schrieb Tvrtko Ursulin:
>>
>> On 08/10/2021 11:21, Christian König wrote:
>>> Am 08.10.21 um 11:50 schrieb Tvrtko Ursulin:
>>>> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>>>>
>>>> Cache the count of shared fences in the iterator to avoid dereferencing
>>>> the dma_resv_object outside the RCU protection. Otherwise iterator 
>>>> and its
>>>> users can observe an incosistent state which makes it impossible to use
>>>> safely.
>>>
>>> Ah, of course! I've been staring at the code the whole morning and 
>>> couldn't see it.
>>>
>>> Going to write a testcase to cover that.
>>>
>>>> Such as:
>>>>
>>>> <6> [187.517041] [IGT] gem_sync: executing
>>>> <7> [187.536343] i915 0000:00:02.0: 
>>>> [drm:i915_gem_context_create_ioctl [i915]] HW context 1 created
>>>> <7> [187.536793] i915 0000:00:02.0: 
>>>> [drm:i915_gem_context_create_ioctl [i915]] HW context 1 created
>>>> <6> [187.551235] [IGT] gem_sync: starting subtest basic-many-each
>>>> <1> [188.935462] BUG: kernel NULL pointer dereference, address: 
>>>> 0000000000000010
>>>> <1> [188.935485] #PF: supervisor write access in kernel mode
>>>> <1> [188.935495] #PF: error_code(0x0002) - not-present page
>>>> <6> [188.935504] PGD 0 P4D 0
>>>> <4> [188.935512] Oops: 0002 [#1] PREEMPT SMP NOPTI
>>>> <4> [188.935521] CPU: 2 PID: 1467 Comm: gem_sync Not tainted 
>>>> 5.15.0-rc4-CI-Patchwork_21264+ #1
>>>> <4> [188.935535] Hardware name:  /NUC6CAYB, BIOS 
>>>> AYAPLCEL.86A.0049.2018.0508.1356 05/08/2018
>>>> <4> [188.935546] RIP: 0010:dma_resv_get_fences+0x116/0x2d0
>>>> <4> [188.935560] Code: 10 85 c0 7f c9 be 03 00 00 00 e8 15 8b df ff 
>>>> eb bd e8 8e c6 ff ff eb b6 41 8b 04 24 49 8b 55 00 48 89 e7 8d 48 01 
>>>> 41 89 0c 24 <4c> 89 34 c2 e8 41 f2 ff ff 49 89 c6 48 85 c0 75 8c 48 
>>>> 8b 44 24 10
>>>> <4> [188.935583] RSP: 0018:ffffc900011dbcc8 EFLAGS: 00010202
>>>> <4> [188.935593] RAX: 0000000000000000 RBX: 00000000ffffffff RCX: 
>>>> 0000000000000001
>>>> <4> [188.935603] RDX: 0000000000000010 RSI: ffffffff822e343c RDI: 
>>>> ffffc900011dbcc8
>>>> <4> [188.935613] RBP: ffffc900011dbd48 R08: ffff88812d255bb8 R09: 
>>>> 00000000fffffffe
>>>> <4> [188.935623] R10: 0000000000000001 R11: 0000000000000000 R12: 
>>>> ffffc900011dbd44
>>>> <4> [188.935633] R13: ffffc900011dbd50 R14: ffff888113d29cc0 R15: 
>>>> 0000000000000000
>>>> <4> [188.935643] FS:  00007f68d17e9700(0000) 
>>>> GS:ffff888277900000(0000) knlGS:0000000000000000
>>>> <4> [188.935655] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>> <4> [188.935665] CR2: 0000000000000010 CR3: 000000012d0a4000 CR4: 
>>>> 00000000003506e0
>>>> <4> [188.935676] Call Trace:
>>>> <4> [188.935685]  i915_gem_object_wait+0x1ff/0x410 [i915]
>>>> <4> [188.935988]  i915_gem_wait_ioctl+0xf2/0x2a0 [i915]
>>>> <4> [188.936272]  ? i915_gem_object_wait+0x410/0x410 [i915]
>>>> <4> [188.936533]  drm_ioctl_kernel+0xae/0x140
>>>> <4> [188.936546]  drm_ioctl+0x201/0x3d0
>>>> <4> [188.936555]  ? i915_gem_object_wait+0x410/0x410 [i915]
>>>> <4> [188.936820]  ? __fget_files+0xc2/0x1c0
>>>> <4> [188.936830]  ? __fget_files+0xda/0x1c0
>>>> <4> [188.936839]  __x64_sys_ioctl+0x6d/0xa0
>>>> <4> [188.936848]  do_syscall_64+0x3a/0xb0
>>>> <4> [188.936859] entry_SYSCALL_64_after_hwframe+0x44/0xae
>>>>
>>>> If the shared object has changed during the RCU unlocked period
>>>> callers will correctly handle the restart on the next iteration.
>>>>
>>>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>>>> Fixes: 96601e8a4755 ("dma-buf: use new iterator in 
>>>> dma_resv_copy_fences")
>>>> Fixes: d3c80698c9f5 ("dma-buf: use new iterator in 
>>>> dma_resv_get_fences v3")
>>>> Closes: 
>>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.freedesktop.org%2Fdrm%2Fintel%2F-%2Fissues%2F4274&data=04%7C01%7Cchristian.koenig%40amd.com%7Cc22feea06a3f4285cdac08d98a495984%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637692870805160909%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=6oPR30sWnJe04I4GlhhvJWX3QvwKFIOMW1uOIyWZFOE%3D&reserved=0 
>>>>
>>>> Cc: Christian König <christian.koenig at amd.com>
>>>> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
>>>> Cc: Sumit Semwal <sumit.semwal at linaro.org>
>>>> Cc: linux-media at vger.kernel.org
>>>> Cc: dri-devel at lists.freedesktop.org
>>>> Cc: linaro-mm-sig at lists.linaro.org
>>>
>>> Maybe we should remove cursor->fences altogether, but either way the 
>>> patch is Reviewed-by: Christian König <christian.koenig at amd.com>
>>>
>>> Please push to drm-misc-next ASAP.
>>
>> Not sure I can or if my push permissions are limited to Intel 
>> branches. I can try once CI gives a green light.
> 
> If it doesn't work just ping me and I will push it.

It finally passed CI but it looks like you'll need to push it:

tursulin at tursulin-mobl2:~/wc/dim/src$ dim push-branch drm-misc-next
Enumerating objects: 15, done.
Counting objects: 100% (15/15), done.
Delta compression using up to 8 threads
Compressing objects: 100% (8/8), done.
Writing objects: 100% (8/8), 2.32 KiB | 593.00 KiB/s, done.
Total 8 (delta 7), reused 0 (delta 0), pack-reused 0
error: remote unpack failed: unable to create temporary object directory
To ssh://git.freedesktop.org/git/drm/drm-misc
  ! [remote rejected]           drm-misc-next -> drm-misc-next (unpacker error)
error: failed to push some refs to 'ssh://git.freedesktop.org/git/drm/drm-misc'

Regards,

Tvrtko