wmTimer, wmJob and WM_report issue - can lead to crash #105369

Closed
opened 2023-03-02 11:32:51 +01:00 by Bastien Montagne · 5 comments

The Problem

Report #105160 unveils a critical issue in wmTimer handling.

Essentially, in several places of WM code timers are looped over in that way:

/* Mutable in case the timer gets removed. */
LISTBASE_FOREACH_MUTABLE (wmTimer *, wt, &wm->timers) {
  ...
}

This is actually not working as expected, because during the processing of a wmTimer, other wmTimers may be added or removed and freed, The latter will lead to a crash if it is the next timer in the list (LISTBASE_FOREACH_MUTABLE only protects against removal/freeing of the current item).

The typical identified case if a job timer updating or ending its job, which job callbacks would call WM_report, which ends up removing/freeing a timer and adding a new one for the report 'popup' in the UI.

Proposed Solutions

This issue has potential solutions at several levels.

1. Simple Fix the Current Issue

The issue with WM_report modifying timers could be addressed by having a flag in the WindowManager marking timers as being processed, in which case WM_report (or more precisely wm_add_reports) should not call WM_report_banner_show.

WM_report_banner_show call could then be added at the end of the loops over wmTimer.

2. More General Fix

Making wmTimer loop safe in general could be achieved by deferring their deletion (tagging them to be deleted, and actually deleting them in a second, safe loop).

### The Problem Report #105160 unveils a critical issue in wmTimer handling. Essentially, in several places of WM code timers are looped over in that way: ``` /* Mutable in case the timer gets removed. */ LISTBASE_FOREACH_MUTABLE (wmTimer *, wt, &wm->timers) { ... } ``` This is actually not working as expected, because during the processing of a wmTimer, other wmTimers may be added or removed and freed, The latter will lead to a crash if it is the next timer in the list (`LISTBASE_FOREACH_MUTABLE` only protects against removal/freeing of the current item). The typical identified case if a job timer updating or ending its job, which job callbacks would call `WM_report`, which ends up removing/freeing a timer and adding a new one for the report 'popup' in the UI. ### Proposed Solutions This issue has potential solutions at several levels. #### 1. Simple Fix the Current Issue The issue with `WM_report` modifying timers could be addressed by having a flag in the WindowManager marking timers as being processed, in which case `WM_report` (or more precisely `wm_add_reports`) should not call `WM_report_banner_show`. `WM_report_banner_show` call could then be added at the end of the loops over wmTimer. #### 2. More General Fix Making wmTimer loop safe in general could be achieved by deferring their deletion (tagging them to be deleted, and actually deleting them in a second, safe loop).
Bastien Montagne added the
Type
Design
Module
Core
labels 2023-03-02 11:32:51 +01:00
Bastien Montagne added this to the 3.5 milestone 2023-03-02 11:33:04 +01:00
Author
Owner

@ideasman42 @brecht, could use your feedback on this one. Think it's a fairly bad issue, and would rather fix it for 3.5 (and backport to previous LTS)?

@ideasman42 @brecht, could use your feedback on this one. Think it's a fairly bad issue, and would rather fix it for 3.5 (and backport to previous LTS)?

I'd go with deferred deletion. I couldn't think of another solution that is watertight.

I'd go with deferred deletion. I couldn't think of another solution that is watertight.
Author
Owner

Committed as d66672e17a.

Committed as d66672e17a.
Blender Bot added the
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Archived
label 2023-03-03 15:34:28 +01:00
Author
Owner

This unfortunately needs to be re-opened, when massively generating reports from threaded code it still causes several issues. Will update description for specific info.

This unfortunately needs to be re-opened, when massively generating reports from threaded code it still causes several issues. Will update description for specific info.
Author
Owner

Actually better use a new task imho: #112537

Actually better use a new task imho: #112537
Blender Bot added
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and removed
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labels 2023-09-18 18:22:40 +02:00
Blender Bot added
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and removed
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labels 2023-09-18 18:44:31 +02:00
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Reference: blender/blender#105369
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