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Currently, runtime.Goexit() calls goexit()—the goroutine exit stub—to terminate the goroutine. This *mostly* works, but can cause a "leftover stack barriers" panic if the following happens: 1. Goroutine A has a reasonably large stack. 2. The garbage collector scan phase runs and installs stack barriers in A's stack. The top-most stack barrier happens to fall at address X. 3. Goroutine A unwinds the stack far enough to be a candidate for stack shrinking, but not past X. 4. Goroutine A calls runtime.Goexit(), which calls goexit(), which calls goexit1(). 5. The garbage collector enters mark termination. 6. Goroutine A is preempted right at the prologue of goexit1() and performs a stack shrink, which calls gentraceback. gentraceback stops as soon as it sees goexit on the stack, which is only two frames up at this point, even though there may really be many frames above it. More to the point, the stack barrier at X is above the goexit frame, so gentraceback never sees that stack barrier. At the end of gentraceback, it checks that it saw all of the stack barriers and panics because it didn't see the one at X. The fix is simple: call goexit1, which actually implements the process of exiting a goroutine, rather than goexit, the exit stub. To make sure this doesn't happen again in the future, we also add an argument to the stub prototype of goexit so you really, really have to want to call it in order to call it. We were able to reliably reproduce the above sequence with a fair amount of awful code inserted at the right places in the runtime, but chose to change the goexit prototype to ensure this wouldn't happen again rather than pollute the runtime with ugly testing code. Change-Id: Ifb6fb53087e09a252baddadc36eebf954468f2a8 Reviewed-on: https://go-review.googlesource.com/13323 Reviewed-by: Russ Cox <rsc@golang.org> |
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The Go Programming Language
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Binary Distribution Notes
If you have just untarred a binary Go distribution, you need to set the environment variable $GOROOT to the full path of the go directory (the one containing this file). You can omit the variable if you unpack it into /usr/local/go, or if you rebuild from sources by running all.bash (see doc/install-source.html). You should also add the Go binary directory $GOROOT/bin to your shell's path.
For example, if you extracted the tar file into $HOME/go, you might put the following in your .profile:
export GOROOT=$HOME/go
export PATH=$PATH:$GOROOT/bin
See https://golang.org/doc/install or doc/install.html for more details.