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Fix #108198: Particle hair crash when using Hair Dynamics #108480

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Hans Goudey merged 2 commits from Chao-Li/blender:fix-hair-dynamics into blender-v3.6-release 2023-06-06 18:46:40 +02:00
Conversation 8 Commits 2 Files Changed 2 +8 -2
Chao Li commented 2023-05-31 21:39:42 +02:00
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hair_out_mesh and hair_in_mesh implicitly shares edges. In hair_create_input_mesh(), edge data of hair_in_mesh needs to be updated and therefore are copied to a new location. In the subsequent frames, psys->clmd->clothObject->edges won't be updated and point to freed memory block. Therefore, Blender crashes.
By freeing hair_out_mesh first,

  1. in hair_create_input_mesh(), at least edge data copying is avoided
  2. psys->clmd->clothObject->edges always points to correct memory

However, since it's possible that similar situation will happen again by adding another strong user to the same CustomData in the future, it is safer to update psys->clmd->clothObject->edges for every frame as well.

hair_out_mesh and hair_in_mesh implicitly shares edges. In hair_create_input_mesh(), edge data of hair_in_mesh needs to be updated and therefore are copied to a new location. In the subsequent frames, psys->clmd->clothObject->edges won't be updated and point to freed memory block. Therefore, Blender crashes. By freeing hair_out_mesh first, 1. in hair_create_input_mesh(), at least edge data copying is avoided 2. psys->clmd->clothObject->edges always points to correct memory However, since it's possible that similar situation will happen again by adding another strong user to the same CustomData in the future, it is safer to update psys->clmd->clothObject->edges for every frame as well.
Iliya Katushenock added this to the Nodes & Physics project 2023-05-31 22:15:35 +02:00
Iliya Katushenock requested review from Hans Goudey 2023-05-31 22:15:53 +02:00
Chao Li force-pushed fix-hair-dynamics from 1653c9840c to 814dffe7bc 2023-06-01 19:17:40 +02:00 Compare
Hans Goudey commented 2023-06-02 19:14:39 +02:00
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@blender-bot build

@blender-bot build
Chao Li commented 2023-06-02 19:55:01 +02:00
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I thought the tests passed on my machine... My apologies. Let me take a look.

I thought the tests passed on my machine... My apologies. Let me take a look.
Chao Li force-pushed fix-hair-dynamics from fd78260038 to e8aff144f2 2023-06-02 22:19:27 +02:00 Compare
Chao Li commented 2023-06-02 22:20:50 +02:00
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I must've rebased before pushing. I rebased again. Now the tests should be good.

I must've rebased before pushing. I rebased again. Now the tests should be good.
Hans Goudey commented 2023-06-02 23:02:46 +02:00
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@blender-bot build

@blender-bot build
Chao Li commented 2023-06-03 19:16:49 +02:00
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Now I think about it I feel like this PR is a performance improvement and a temporary fix. I think the real problem is not properly addressed: it is assumed that some CustomData won't be moved during computation. Let's say somehow a new piece of code is introduced and another strong user is added to the hair_in_mesh->edata, the hair dynamics will be broken again. We should always assume the CustomData can be moved to a new place, maybe?

Now I think about it I feel like this PR is a performance improvement and a temporary fix. I think the real problem is not properly addressed: it is assumed that some CustomData won't be moved during computation. Let's say somehow a new piece of code is introduced and another strong user is added to the hair_in_mesh->edata, the hair dynamics will be broken again. We should always assume the CustomData can be moved to a new place, maybe?
Chao Li changed title from Fix #108198: Particle hair crash when using Hair Dynamics to WIP: Fix #108198: Particle hair crash when using Hair Dynamics 2023-06-03 19:17:28 +02:00
Chao Li changed title from WIP: Fix #108198: Particle hair crash when using Hair Dynamics to Fix #108198: Particle hair crash when using Hair Dynamics 2023-06-03 22:50:11 +02:00
Chao Li commented 2023-06-03 23:04:10 +02:00
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Added another commit to update edge in simulation data for every frame. Please let me know if there other better workarounds. Thank you.

Added another commit to update edge in simulation data for every frame. Please let me know if there other better workarounds. Thank you.
Hans Goudey commented 2023-06-05 16:35:51 +02:00
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Since the particle system is end of life, I'm not too concerned about whether this is the perfect solution. A workaround is fine, and this code looks reasonable.

Could you rebase the PR to target the blender-v3.6-release branch, since the bug exists there too? More info here: https://wiki.blender.org/wiki/Tools/Pull_Requests#Rebasing_a_Pull_Request

Thanks!

Since the particle system is end of life, I'm not too concerned about whether this is the perfect solution. A workaround is fine, and this code looks reasonable. Could you rebase the PR to target the `blender-v3.6-release` branch, since the bug exists there too? More info here: https://wiki.blender.org/wiki/Tools/Pull_Requests#Rebasing_a_Pull_Request Thanks!
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Chao Li changed title from Fix #108198: Particle hair crash when using Hair Dynamics to Fix #108198: Particle hair crash when using Hair Dynamics 2023-06-05 16:40:21 +02:00
Chao-Li changed target branch from main to blender-v3.6-release 2023-06-05 16:40:24 +02:00
Chao Li force-pushed fix-hair-dynamics from 6fcc4d5fbd to fd78260038 2023-06-05 16:47:11 +02:00 Compare
Chao Li force-pushed fix-hair-dynamics from fd78260038 to 08f8b8b266 2023-06-05 16:48:16 +02:00 Compare
Chao Li commented 2023-06-05 17:36:45 +02:00
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Got it.

I've rebased the PR. Tests look good on my machine.

Thank you.

Got it. I've rebased the PR. Tests look good on my machine. Thank you.
Hans Goudey merged commit a56df90931 into blender-v3.6-release 2023-06-06 18:46:40 +02:00
Chao Li deleted branch fix-hair-dynamics 2023-06-13 23:31:26 +02:00
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