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runtime: block signals in needm before allocating M

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Otherwise, if a signal occurs just after we allocated the M,
we can deadlock if the signal handler needs to allocate an M
itself.

Fixes #42207

Change-Id: I76f44547f419e8b1c14cbf49bf602c6e645d8c14
Reviewed-on: https://go-review.googlesource.com/c/go/+/265759
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
This commit is contained in:
Ian Lance Taylor 2020-10-27 16:09:40 -07:00
parent 94f3762462
commit 368c401164
7 changed files with 127 additions and 17 deletions
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8
src/runtime/signal_unix.go
View file

@ -1031,15 +1031,15 @@ func sigfwdgo(sig uint32, info *siginfo, ctx unsafe.Pointer) bool {
return true
}
// msigsave saves the current thread's signal mask into mp.sigmask.
// sigsave saves the current thread's signal mask into *p.
// This is used to preserve the non-Go signal mask when a non-Go
// thread calls a Go function.
// This is nosplit and nowritebarrierrec because it is called by needm
// which may be called on a non-Go thread with no g available.
//go:nosplit
//go:nowritebarrierrec
func msigsave(mp *m) {
sigprocmask(_SIG_SETMASK, nil, &mp.sigmask)
func sigsave(p *sigset) {
sigprocmask(_SIG_SETMASK, nil, p)
}
// msigrestore sets the current thread's signal mask to sigmask.
@ -1111,7 +1111,7 @@ func minitSignalStack() {
// thread's signal mask. When this is called all signals have been
// blocked for the thread. This starts with m.sigmask, which was set
// either from initSigmask for a newly created thread or by calling
// msigsave if this is a non-Go thread calling a Go function. It
// sigsave if this is a non-Go thread calling a Go function. It
// removes all essential signals from the mask, thus causing those
// signals to not be blocked. Then it sets the thread's signal mask.
// After this is called the thread can receive signals.