rt: fix bug in work-stealing queue #2387
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Fixes a couple bugs in the work-stealing queue introduced as part of #2315. First, the cursor needs to be able to represent more values than the size of the buffer. This is to be able to track if `tail` is ahead of `head` or if they are identical. This bug resulted in the "overflow" path being taken before the buffer was full. The second bug can happen when a queue is being stolen from concurrently with stealing into. In this case, it is possible for buffer slots to be overwritten before they are released by the stealer. This is harder to happen in practice due to the first bug preventing the queue from filling up 100%, but could still happen. It triggered an assertion in `steal_into`. This bug slipped through due to a bug in loom not correctly catching the case. The loom bug is fixed as part of tokio-rs/loom#119. Fixes: #2382
hawkw
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Apr 9, 2020
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The FreeBSD CI build failure is due to some kind of CI issue (possibly something in Cirrus is broken?), so per a conversation with Carl, we're ignoring it for now. |
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- rt: bug in work-stealing queue (#2387) Signed-off-by: Eliza Weisman <eliza@buoyant.io>
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- rt: bug in work-stealing queue (#2387) Signed-off-by: Eliza Weisman <eliza@buoyant.io>
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Fixes a couple bugs in the work-stealing queue introduced as
part of #2315. First, the cursor needs to be able to represent more
values than the size of the buffer. This is to be able to track if
tailis ahead ofheador if they are identical. This bug resulted inthe "overflow" path being taken before the buffer was full.
The second bug can happen when a queue is being stolen from concurrently
with stealing into. In this case, it is possible for buffer slots to be
overwritten before they are released by the stealer. This is harder to
happen in practice due to the first bug preventing the queue from
filling up 100%, but could still happen. It triggered an assertion in
steal_into. This bug slipped through due to a bug in loom notcorrectly catching the case. The loom bug is fixed as part of
tokio-rs/loom#119.
Fixes: #2382