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net: data race with uninstallTestHooks #21090

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aclements opened this issue Jul 19, 2017 · 5 comments
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net: data race with uninstallTestHooks #21090

aclements opened this issue Jul 19, 2017 · 5 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done. Testing An issue that has been verified to require only test changes, not just a test failure.
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Go1.10

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@aclements
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A race between net.uninstallTestHooks and internal/poll.(*FD).destroy() on linux-amd64-race has appeared on the dashboard a few times:

2017-06-25T15:57:18-b4dd1d9/linux-amd64-race
2017-07-10T20:09:00-6f83b75/linux-amd64-race
2017-07-15T20:44:10-0b62ebf/linux-amd64-race
2017-07-15T20:49:42-7390d2f/linux-amd64-race

And just appeared on a trybot: https://go-review.googlesource.com/c/50030/
@aclements aclements added the Testing An issue that has been verified to require only test changes, not just a test failure. label Jul 19, 2017
@bradfitz
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/cc @mikioh @ianlancetaylor

@bradfitz bradfitz added the NeedsFix The path to resolution is known, but the work has not been done. label Jul 19, 2017
@bradfitz bradfitz added this to the Go1.10 milestone Jul 19, 2017
@ianlancetaylor
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Seems like the problem is that a cancelled DNS lookup can leave behind a goroutine that has a deferred close of a DNS connection (the defer c.Close() in (*Resolver).exchange). There is no synchronization between that deferred close and the call to uninstallTestHooks in TestMain. uninstallTestHooks changes poll.CloseFunc, which is called when closing a connection. Ideally we should wait for all goroutines to complete before uninstalling the test hook, but at present there is no obvious way to do that.

@bradfitz bradfitz mentioned this issue Aug 3, 2017
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@ianlancetaylor ianlancetaylor mentioned this issue Aug 25, 2017
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@josharian
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Just failed again on a trybot: https://storage.googleapis.com/go-build-log/f8bd34ff/linux-amd64-race_a10fd3d5.log

@bradfitz bradfitz mentioned this issue Aug 28, 2017
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@bradfitz
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And again:
https://storage.googleapis.com/go-build-log/e8ca7680/linux-amd64-race_9d82113e.log

@gopherbot
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Change https://golang.org/cl/82795 mentions this issue: net: avoid race on test hooks with DNS goroutines

@mikioh mikioh mentioned this issue Jan 12, 2018
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@golang golang locked and limited conversation to collaborators Dec 8, 2018
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done. Testing An issue that has been verified to require only test changes, not just a test failure.
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@bradfitz @josharian @aclements @ianlancetaylor @gopherbot