progress: fix sync issue in controller. #2641
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A panic was encountered where writes to progress status hit a nil writer. While not easy to reproduce, this commit fixes a likely culprit. The use of atomics in the controller was not safe against a race such as the following: 1. One goroutine calls Start, incrementing count but not yet setting writer. 2. A second goroutine calls Start, increments count again but sees that count >1 and thus doesn't try to set writer. 3. The second goroutine then calls Status, assuming the writer has been set, but the first goroutine still hasn't set the writer yet, causing a nil pointer exception. This commit fixes that issue by just using a mutex instead of atomics. It also adds a nil check for the writer just to be safe against panics due to unknown issues in the future as missing a status update is much better than buildkitd crashing. Signed-off-by: Erik Sipsma <[email protected]>
tonistiigi
approved these changes
Feb 16, 2022
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Will this be included in v0.10.0-rc2? |
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A panic was encountered where writes to progress status hit a nil
writer. While not easy to reproduce, this commit fixes a likely culprit.
The use of atomics in the controller was not safe against a race such as
the following:
writer.
count >1 and thus doesn't try to set writer.
set, but the first goroutine still hasn't set the writer yet, causing
a nil pointer exception.
This commit fixes that issue by just using a mutex instead of atomics.
It also adds a nil check for the writer just to be safe against panics
due to unknown issues in the future as missing a status update is much
better than buildkitd crashing.
Signed-off-by: Erik Sipsma [email protected]
This address the panic mentioned in the comment here, though the problem is unrelated to that PR: #2611 (comment)