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time, runtime: scheduled timer may never fire if GOMAXPROCS is reduced [1.15 backport] #45731

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gopherbot opened this issue Apr 23, 2021 · 5 comments
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time, runtime: scheduled timer may never fire if GOMAXPROCS is reduced [1.15 backport] #45731

gopherbot opened this issue Apr 23, 2021 · 5 comments
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CherryPickApproved Used during the release process for point releases FrozenDueToAge release-blocker
Milestone
Go1.15.12

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@gopherbot
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@ianlancetaylor requested issue #45716 to be considered for backport to the next 1.15 minor release.

@gopherbot Please open backport to 1.15 branch.
@gopherbot gopherbot added the CherryPickCandidate Used during the release process for point releases label Apr 23, 2021
@gopherbot gopherbot mentioned this issue Apr 23, 2021
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@gopherbot gopherbot added this to the Go1.15.12 milestone Apr 23, 2021
@ianlancetaylor
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This was already fixed on the 1.16 branch by CL 300610. This issue is to backport that CL to the 1.15 branch as well.

@gopherbot
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Change https://golang.org/cl/313130 mentions this issue: [release-branch.go1.15] runtime, time: disable preemption in addtimer

@gopherbot
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Change https://golang.org/cl/313129 mentions this issue: [release-branch.go1.15] runtime, time: disable preemption in addtimer

@toothrot toothrot added the CherryPickApproved Used during the release process for point releases label Apr 29, 2021
@toothrot
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Approved. This is a serious issue with no workaround.

@gopherbot gopherbot removed the CherryPickCandidate Used during the release process for point releases label Apr 29, 2021
@gopherbot
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Closed by merging 72ccabc to release-branch.go1.15.

gopherbot pushed a commit that referenced this issue Apr 29, 2021
@prattmic @ianlancetaylor
[release-branch.go1.15] runtime, time: disable preemption in addtimer
72ccabc 
The timerpMask optimization updates a mask of Ps (potentially)
containing timers in pidleget / pidleput. For correctness, it depends on
the assumption that new timers can only be added to a P's own heap.

addtimer violates this assumption if it is preempted after computing pp.
That G may then run on a different P, but adding a timer to the original
P's heap.

Avoid this by disabling preemption while pp is in use.

Other uses of doaddtimer should be OK:

* moveTimers: always moves to the current P's heap
* modtimer, cleantimers, addAdjustedTimers, runtimer: does not add net
  new timers to the heap while locked

For #44868
Fixes #45731

Change-Id: I4a5d080865e854931d0a3a09a51ca36879101d72
Reviewed-on: https://go-review.googlesource.com/c/go/+/300610
Trust: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-on: https://go-review.googlesource.com/c/go/+/313129
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
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