deadok22
commented
2 years ago Here's a Go playground link with a simplified example of the same flavor of a data race.
package main
const (
allowedThirdValue1 = "a-third-value"
allowedThirdValue2 = "another-third-value"
)
func checkTheThird(tags chan []string) {
for {
v := (<-tags)[2]
switch v {
case allowedThirdValue1, allowedThirdValue2:
default:
panic("read something unexpected: " + v)
}
}
}
func main() {
tags := make([]string, 0, 3)
tags = append(tags, "one", "two")
tagsCh := make(chan []string, 42)
go checkTheThird(tagsCh)
for {
tagsCh <- append(tags, allowedThirdValue1)
tagsCh <- append(tags, allowedThirdValue2)
}
}
knusbaum
There are data races due to these append() calls in pkg/trace/info/stats.go.
The
append(tags, ...)calls linked to above can modify the array backing thetagsslice, if the array's capacity is larger than the slice's size, while the code backingmetrics.Countreads the same array. Note that the code backingmetrics.Countmay access thelen(tags)-th array element while it's being written to by another goroutine. This can lead to all sorts of trouble (reading arbitrary memory, segfaults, etc.).