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runtime: eliminate write barriers from save

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As for dropg, save is writing a nil pointer that will generate a write
barrier with the hybrid barrier. However, in this case, ctxt always
should already be nil, so replace the write with an assertion that
this is the case.

At this point, we're ready to disable the write barrier elision
optimizations that interfere with the hybrid barrier.

Updates #17503.

Change-Id: I83208e65aa33403d442401f355b2e013ab9a50e9
Reviewed-on: https://go-review.googlesource.com/31571
Reviewed-by: Rick Hudson <rlh@golang.org>
This commit is contained in:
Austin Clements 2016-10-19 16:16:40 -04:00
parent 8044b77a57
commit c3163d23f0
1 changed files with 17 additions and 1 deletions
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18
src/runtime/proc.go
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@ -399,6 +399,11 @@ func badmorestackgsignal() {
write(2, sp.str, int32(sp.len))
}
//go:nosplit
func badctxt() {
throw("ctxt != 0")
}
func lockedOSThread() bool {
gp := getg()
return gp.lockedm != nil && gp.m.lockedg != nil
@ -2285,6 +2290,12 @@ func goexit0(gp *g) {
schedule()
}
// save updates getg().sched to refer to pc and sp so that a following
// gogo will restore pc and sp.
//
// save must not have write barriers because invoking a write barrier
// can clobber getg().sched.
//
//go:nosplit
//go:nowritebarrierrec
func save(pc, sp uintptr) {
@ -2294,8 +2305,13 @@ func save(pc, sp uintptr) {
_g_.sched.sp = sp
_g_.sched.lr = 0
_g_.sched.ret = 0
_g_.sched.ctxt = nil
_g_.sched.g = guintptr(unsafe.Pointer(_g_))
// We need to ensure ctxt is zero, but can't have a write
// barrier here. However, it should always already be zero.
// Assert that.
if _g_.sched.ctxt != nil {
badctxt()
}
}
// The goroutine g is about to enter a system call.