julia_gc: fix detection of already scanned root task #5726
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fingolfin
added
topic: kernel
release notes: not needed
We already scan some stack during as part of the `GapRootScanner` callback, which usually will be the stack of the active task of the main thread. As an optimization, we want to avoid scanning that task's thread a second time in `GapTaskScanner`. We used to do that by checking in the latter whether the task about to be scanned is the current task. But that is wrong: the task may be different for all kinds of reasons, most notably if there are multiple GC threads active. So instead, just record the task we scanned in `GapRootScanner` (this is safe to write as there is single thread involved at this point) and then compare against that in `GapTaskScanner` (which may be called concurrently from multiple threads).
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ChrisJefferson
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May 28, 2024
fingolfin
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We already scan some stack during as part of the
GapRootScannercallback, which usually will be the stack of the active task of the main thread. As an optimization, we want to avoid scanning that task's thread a second time inGapTaskScanner.We used to do that by checking in the latter whether the task about to be scanned is the current task. But that is wrong: the task may be different for all kinds of reasons, most notably if there are multiple GC threads active.
So instead, just record the task we scanned in
GapRootScanner(this is safe to write as there is single thread involved at this point) and then compare against that inGapTaskScanner(which may be called concurrently from multiple threads).