syscall: syscall.AllThreadsSyscall signal handling fixes

The runtime support for syscall.AllThreadsSyscall() functions had
some corner case deadlock issues when signal handling was in use.
This was observed in at least 3 build test failures on ppc64 and
amd64 architecture CGO_ENABLED=0 builds over the last few months.

The fixes involve more controlled handling of signals while the
AllThreads mechanism is being executed. Further details are
discussed in bug #44193.

The all-threads syscall support is new in go1.16, so earlier
releases are not affected by this bug.

Fixes #44193

Change-Id: I01ba8508a6e1bb2d872751f50da86dd07911a41d
Reviewed-on: https://go-review.googlesource.com/c/go/+/305149
Reviewed-by: Michael Pratt <mpratt@google.com>
Trust: Michael Pratt <mpratt@google.com>
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/runtime/sigqueue.go b/src/runtime/sigqueue.go
index aae1d00046..6c91fb3fb3 100644
--- a/src/runtime/sigqueue.go
+++ b/src/runtime/sigqueue.go
@@ -120,7 +120,7 @@ Send:
 			}
 		case sigFixup:
 			// nothing to do - we need to wait for sigIdle.
-			osyield()
+			mDoFixupAndOSYield()
 		}
 	}