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go/types: data race in Checker.underlying #34921

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rsc opened this issue Oct 15, 2019 · 3 comments
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go/types: data race in Checker.underlying #34921

rsc opened this issue Oct 15, 2019 · 3 comments
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Go1.14

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@rsc
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rsc commented Oct 15, 2019

CL 196338, fixing #34333, introduced a data race by caching the result in n.underlying without protecting n with a lock.

Previously, if you had packages A and B both importing C, it was safe to run types.NewChecker(...).Files() on package C's files and then type-check A and B in parallel goroutines both of which returned C's type-check information from their types.Config.Importer.

But now both A and B might end up calling underlying or Underlying on the same type, and the writes updating the new cached value race. For example, here is one trace from #31749:

    WARNING: DATA RACE
    Read at 0x00c0022767f0 by goroutine 200:
      go/types.(*Named).Underlying()
          /workdir/go/src/go/types/type.go:511 +0x3e
      go/types.isTyped()
          /workdir/go/src/go/types/predicates.go:55 +0x83
      go/types.(*Checker).typeDecl()
          /workdir/go/src/go/types/decl.go:544 +0x458
      go/types.(*Checker).objDecl()
          /workdir/go/src/go/types/decl.go:192 +0xcae
      go/types.(*Checker).packageObjects()
          /workdir/go/src/go/types/resolver.go:569 +0x53f
      go/types.(*Checker).checkFiles()
          /workdir/go/src/go/types/check.go:255 +0xd7
      go/types.(*Checker).Files()
          /workdir/go/src/go/types/check.go:246 +0xd3c
      golang.org/x/tools/go/packages.(*loader).loadRecursive.func1()
          /workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:685 +0x258
      sync.(*Once).doSlow()
          /workdir/go/src/sync/once.go:66 +0x100
      sync.(*Once).Do()
          /workdir/go/src/sync/once.go:57 +0x68
      golang.org/x/tools/go/packages.(*loader).loadRecursive()
          /workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:673 +0x74
      golang.org/x/tools/go/packages.(*loader).loadRecursive.func1.1()
          /workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:680 +0x42
    
    Previous write at 0x00c0022767f0 by goroutine 339:
      go/types.(*Checker).underlying()
          /workdir/go/src/go/types/decl.go:513 +0x5a6
      go/types.(*Checker).typeDecl()
          /workdir/go/src/go/types/decl.go:559 +0x4ca
      go/types.(*Checker).objDecl()
          /workdir/go/src/go/types/decl.go:192 +0xcae
      go/types.(*Checker).packageObjects()
          /workdir/go/src/go/types/resolver.go:569 +0x53f
      go/types.(*Checker).checkFiles()
          /workdir/go/src/go/types/check.go:255 +0xd7
      go/types.(*Checker).Files()
          /workdir/go/src/go/types/check.go:246 +0xd3c
      golang.org/x/tools/go/packages.(*loader).loadRecursive.func1()
          /workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:685 +0x258
      sync.(*Once).doSlow()
          /workdir/go/src/sync/once.go:66 +0x100
      sync.(*Once).Do()
          /workdir/go/src/sync/once.go:57 +0x68
      golang.org/x/tools/go/packages.(*loader).loadRecursive()
          /workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:673 +0x74
      golang.org/x/tools/go/packages.(*loader).loadRecursive.func1.1()
          /workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:680 +0x42
@rsc rsc added this to the Go1.14 milestone Oct 15, 2019
@rsc
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rsc commented Oct 15, 2019

The same CL also introduced a similar race in validType. Again from #31749:

    WARNING: DATA RACE
    Read at 0x00c0007ce550 by goroutine 63:
      go/types.(*Checker).validType()
          /workdir/go/src/go/types/decl.go:320 +0x48c
      go/types.(*Checker).validType()
          /workdir/go/src/go/types/decl.go:323 +0x826
      go/types.(*Checker).typeDecl.func1()
          /workdir/go/src/go/types/decl.go:529 +0x8f
      go/types.(*Checker).processDelayed()
          /workdir/go/src/go/types/check.go:281 +0x5a
      go/types.(*Checker).checkFiles()
          /workdir/go/src/go/types/check.go:257 +0xf1
      go/types.(*Checker).Files()
          /workdir/go/src/go/types/check.go:246 +0xd3c
      golang.org/x/tools/go/packages.(*loader).loadRecursive.func1()
          /workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:685 +0x258
      sync.(*Once).doSlow()
          /workdir/go/src/sync/once.go:66 +0x100
      sync.(*Once).Do()
          /workdir/go/src/sync/once.go:57 +0x68
      golang.org/x/tools/go/packages.(*loader).loadRecursive()
          /workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:673 +0x74
      golang.org/x/tools/go/packages.(*loader).loadRecursive.func1.1()
          /workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:680 +0x42
    
    Previous write at 0x00c0007ce550 by goroutine 67:
      go/types.(*Checker).validType()
          /workdir/go/src/go/types/decl.go:322 +0x708
      go/types.(*Checker).validType()
          /workdir/go/src/go/types/decl.go:301 +0x249
      go/types.(*Checker).validType()
          /workdir/go/src/go/types/decl.go:323 +0x826
      go/types.(*Checker).typeDecl.func1()
          /workdir/go/src/go/types/decl.go:529 +0x8f
      go/types.(*Checker).processDelayed()
          /workdir/go/src/go/types/check.go:281 +0x5a
      go/types.(*Checker).checkFiles()
          /workdir/go/src/go/types/check.go:257 +0xf1
      go/types.(*Checker).Files()
          /workdir/go/src/go/types/check.go:246 +0xd3c
      golang.org/x/tools/go/packages.(*loader).loadRecursive.func1()
          /workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:685 +0x258
      sync.(*Once).doSlow()
          /workdir/go/src/sync/once.go:66 +0x100
      sync.(*Once).Do()
          /workdir/go/src/sync/once.go:57 +0x68
      golang.org/x/tools/go/packages.(*loader).loadRecursive()
          /workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:673 +0x74
      golang.org/x/tools/go/packages.(*loader).loadRecursive.func1.1()
          /workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:680 +0x42

@rsc rsc mentioned this issue Oct 15, 2019
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@matloob
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matloob commented Oct 15, 2019

This matches up with what I've been seeing. Before CL 196338 it was okay to concurrently type-check two packages that depend on the same package, which golang.org/x/tools/go/packages does, but not after. I've been running into the second (validType) race consistently.

@griesemer
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Fixed by https://golang.org/cl/201838 (but the CL mentioned #31749 by mistake).

@bcmills bcmills mentioned this issue Oct 21, 2019
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