runtime: -race data race map traceback report incorrect functions

[prattmic]

The fast variant swissmap functions report the wrong PC to TSAN in their custom instrumentation, which results in incorrect stack traces when races are found and GOTRACEBACK=system or higher (by default the runtime frame is hidden).

package main

func main() {
        m := make(map[int]int)
        go func() {
                for {
                        _ = m[1]
                }
        }()
        go func() {
                for {
                        m[1] = 1
                }
        }()
        select {}
}

$ GOTRACEBACK=system go run -race main.go
==================
WARNING: DATA RACE
Read at 0x00c000034030 by goroutine 6:
  runtime.mapaccess1()
      /usr/lib/google-golang/src/internal/runtime/maps/runtime_swiss.go:43 +0x0
  main.main.func1()
      /tmp/racemap/main.go:7 +0x3a

Previous write at 0x00c000034030 by goroutine 7:
  runtime.mapassign()
      /usr/lib/google-golang/src/internal/runtime/maps/runtime_swiss.go:191 +0x0
  main.main.func2()
      /tmp/racemap/main.go:12 +0x3a

Goroutine 6 (running) created at:
  main.main()
      /tmp/racemap/main.go:5 +0x7c

Goroutine 7 (running) created at:
  main.main()
      /tmp/racemap/main.go:10 +0xc6
==================
fatal error: concurrent map read and map write

goroutine 5 gp=0xc000003dc0 m=5 mp=0xc000088008 [running]:
runtime.fatal({0x4bbb40, 0x21})
        /usr/lib/google-golang/src/runtime/panic.go:1134 +0x5c fp=0xc000049760 sp=0xc000049730 pc=0x46949c
internal/runtime/maps.fatal({0x4bbb40?, 0x4a1939?})
        /usr/lib/google-golang/src/runtime/panic.go:1067 +0x18 fp=0xc000049780 sp=0xc000049760 pc=0x49ad38
runtime.mapaccess1_fast64(0x4ad660, 0xc000034030, 0x1)
        /usr/lib/google-golang/src/internal/runtime/maps/runtime_fast64_swiss.go:29 +0xfe fp=0xc0000497b0 sp=0xc000049780 pc=0x43b61e
main.main.func1()
        /tmp/racemap/main.go:7 +0x3b fp=0xc0000497e0 sp=0xc0000497b0 pc=0x4a3b7b
runtime.goexit({})
        /usr/lib/google-golang/src/runtime/asm_amd64.s:1700 +0x1 fp=0xc0000497e8 sp=0xc0000497e0 pc=0x4a02a1
created by main.main in goroutine 1
        /tmp/racemap/main.go:5 +0x7d
...

In the DATA RACE report, the read should say runtime.mapaccess1_fast64, not runtime.mapaccess1 and the write should say runtime.mapassign_fast64, not runtime.mapassign.

Note that the always-enabled concurrent map read/write throw got the stack correct because it is just a normal throw, but that isn't guaranteed to catch a race when TSAN does.

Thanks @mateusz834 for finding this.

[prattmic]

@gopherbot Please backport to 1.24. This is a minor issue. DATA RACE reports for races in fast-variant maps (int or string keys) will report the wrong map function (e.g., mapassign vs mapassign_fast32). This is a reporting issue only that may cause confusion for readers, as it seems to be an "impossible" call that doesn't appear in the assembly. The most confusing one is map delete, which will report as map assign. This only affects GOTRACEBACK=system or higher because we otherwise hide the runtime function anyway.

[gopherbot]

Backport issue(s) opened: #73192 (for 1.24).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.

[gabyhelp]

Related Issues

• runtime/race: document and fix "trap when race detected" #23577
• runtime: concurrent map access detection in hashmap.go only catches one stack #26703 (closed)
• runtime/race: tracebacks missing symbol/file names #60245 (closed)
• runtime: concurrent map iter+write fatal doesn't respect GOTRACEBACK #68019
• runtime/race: panic+recover in init() adds extra info to data race stack traces in main() #46095
• runtime: GC from cgo callbacks is broken #5899 (closed)
• runtime: crash in race detector when execution tracer reads from CPU profile buffer #65607 (closed)
• runtime/race: goroutine IDs in race failures are incorrect #28284
• runtime: fatal error stack traces are swallowed for binaries with elevated privileges #68103

Related Code Changes

• runtime: respect GOTRACEBACK for user-triggered runtime panics

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[gopherbot]

Change https://go.dev/cl/663175 mentions this issue: internal/runtime/maps: pass proper func PC to race.WritePC/race.ReadPC

[gopherbot]

Change https://go.dev/cl/663777 mentions this issue: [release-branch.go1.24] internal/runtime/maps: pass proper func PC to race.WritePC/race.ReadPC