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runtime,go/token: data race on FileSet.last #48940

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bcmills opened this issue Oct 13, 2021 · 5 comments
Closed

runtime,go/token: data race on FileSet.last #48940

bcmills opened this issue Oct 13, 2021 · 5 comments
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FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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Backlog

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@bcmills
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bcmills commented Oct 13, 2021

greplogs --dashboard -md -l -e '(?m)WARNING: DATA RACE\n.*\n go/token'

2021-10-13T00:11:47-4fb2e1c/freebsd-amd64-race

See previously #4345.
@bcmills bcmills added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Oct 13, 2021
@bcmills bcmills added this to the Backlog milestone Oct 13, 2021
@bcmills
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bcmills commented Oct 13, 2021 

==================
WARNING: DATA RACE
Read at 0x00c0001de038 by goroutine 58:
  go/token.(*FileSet).file()
      /tmp/workdir/go/src/go/token/position.go:476 +0x4a
  go/token.(*FileSet).PositionFor()
      /tmp/workdir/go/src/go/token/position.go:514 +0x5e
  go/ast.lineAt()
      /tmp/workdir/go/src/go/ast/import.go:56 +0x3e5
  go/ast.SortImports()
      /tmp/workdir/go/src/go/ast/import.go:45 +0x3ce
  go/format.Node()
      /tmp/workdir/go/src/go/format/format.go:82 +0x384
  cmd/fix.gofmtFile()
      /tmp/workdir/go/src/cmd/fix/main.go:110 +0xa8
  cmd/fix.parseFixPrint()
      /tmp/workdir/go/src/cmd/fix/main_test.go:68 +0x434
  cmd/fix.TestRewrite.func1()
      /tmp/workdir/go/src/cmd/fix/main_test.go:109 +0x36e
  testing.tRunner()
      /tmp/workdir/go/src/testing/testing.go:1377 +0x213
  testing.(*T).Run.func1()
      /tmp/workdir/go/src/testing/testing.go:1424 +0x47

Previous write at 0x00c0001de038 by goroutine 16:
  go/token.(*FileSet).file()
      /tmp/workdir/go/src/go/token/position.go:487 +0x1ce
  go/token.(*FileSet).PositionFor()
      /tmp/workdir/go/src/go/token/position.go:514 +0x5e
  go/printer.(*printer).lineFor()
      /tmp/workdir/go/src/go/printer/printer.go:204 +0x47d
  go/printer.(*printer).exprList()
      /tmp/workdir/go/src/go/printer/nodes.go:148 +0x3b0
  go/printer.(*printer).spec()
      /tmp/workdir/go/src/go/printer/nodes.go:1628 +0x3f0
  go/printer.(*printer).genDecl()
      /tmp/workdir/go/src/go/printer/nodes.go:1691 +0x479
  go/printer.(*printer).decl()
      /tmp/workdir/go/src/go/printer/nodes.go:1839 +0xa6
  go/printer.(*printer).declList()
      /tmp/workdir/go/src/go/printer/nodes.go:1884 +0x544
  go/printer.(*printer).file()
      /tmp/workdir/go/src/go/printer/nodes.go:1892 +0x14e
  go/printer.(*printer).printNode()
      /tmp/workdir/go/src/go/printer/printer.go:1159 +0x85c
  go/printer.(*Config).fprint()
      /tmp/workdir/go/src/go/printer/printer.go:1316 +0x1af
  go/printer.(*Config).Fprint()
      /tmp/workdir/go/src/go/printer/printer.go:1378 +0x4d5
  go/format.Node()
      /tmp/workdir/go/src/go/format/format.go:91 +0x3e
  cmd/fix.gofmtFile()
      /tmp/workdir/go/src/cmd/fix/main.go:110 +0xa8
  cmd/fix.parseFixPrint()
      /tmp/workdir/go/src/cmd/fix/main_test.go:68 +0x434
  cmd/fix.TestRewrite.func1()
      /tmp/workdir/go/src/cmd/fix/main_test.go:83 +0x84
  testing.tRunner()
      /tmp/workdir/go/src/testing/testing.go:1377 +0x213
  testing.(*T).Run.func1()
      /tmp/workdir/go/src/testing/testing.go:1424 +0x47

Goroutine 58 (running) created at:
  testing.(*T).Run()
      /tmp/workdir/go/src/testing/testing.go:1424 +0x724
  cmd/fix.TestRewrite()
      /tmp/workdir/go/src/cmd/fix/main_test.go:80 +0x1a4
  testing.tRunner()
      /tmp/workdir/go/src/testing/testing.go:1377 +0x213
  testing.(*T).Run.func1()
      /tmp/workdir/go/src/testing/testing.go:1424 +0x47

Goroutine 16 (running) created at:
  testing.(*T).Run()
      /tmp/workdir/go/src/testing/testing.go:1424 +0x724
  cmd/fix.TestRewrite()
      /tmp/workdir/go/src/cmd/fix/main_test.go:80 +0x1a4
  testing.tRunner()
      /tmp/workdir/go/src/testing/testing.go:1377 +0x213
  testing.(*T).Run.func1()
      /tmp/workdir/go/src/testing/testing.go:1424 +0x47
==================

@bcmills
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bcmills commented Oct 13, 2021

The odd thing about this race is that both the read and the write appear to be synchronized.

The read is here, under an RLock:

go/src/go/token/position.go

Lines 474 to 479 in e8f99da

s.mutex.RLock()
// common case: p is in last file
if f := s.last; f != nil && f.base <= int(p) && int(p) <= f.base+f.size {
s.mutex.RUnlock()
return f
}

The write is here, under a write-lock:

go/src/go/token/position.go

Lines 485 to 489 in e8f99da

s.mutex.RUnlock()
s.mutex.Lock()
s.last = f // race is ok - s.last is only a cache
s.mutex.Unlock()
return f

@bcmills
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bcmills commented Oct 14, 2021

For now the best theory I have for this failure is “unrelated memory corruption” (#46272). 🤷‍♂️

@bcmills bcmills changed the title go/token: data race on FileSet.last runtime,go/token: data race on FileSet.last Oct 14, 2021
@bcmills
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bcmills commented Jan 12, 2022

No more of these since October.

greplogs --dashboard -md -l -e '(?m)WARNING: DATA RACE\n.*\n go/token' --since=2021-10-14

@bcmills
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bcmills commented Jan 12, 2022

Duplicate of #46272

@bcmills bcmills marked this as a duplicate of #46272 Jan 12, 2022
@bcmills bcmills closed this as completed Jan 12, 2022
@golang golang locked and limited conversation to collaborators Jan 12, 2023
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