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[dev.typeparams] Revert "[dev.typeparams] runtime: remove unnecessary split-prevention from defer code"

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This reverts CL 337651.

This causes `go test -count 1000 -run TestDeferHeapAndStack runtime`
to fail with a SIGSEGV freedefer
[https://build.golang.org/log/c113b366cc6d51146db02a07b4d7dd931133efd5]
and possibly sometimes a GC bad pointer panic
[https://build.golang.org/log/5b1cef7a9ad68704e9ef3ce3ad2fefca3ba86998].

Change-Id: Ie56c274b78603c81191213b302225ae19de27fb9
Reviewed-on: https://go-review.googlesource.com/c/go/+/338710
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
Austin Clements 2021-07-30 16:41:11 -04:00
parent e3e9f0bb2d
commit 7bed50e667
1 changed files with 55 additions and 29 deletions
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36
src/runtime/panic.go
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@ -261,8 +261,10 @@ func deferproc(fn func()) {
// deferprocStack queues a new deferred function with a defer record on the stack.
// The defer record must have its fn field initialized.
// All other fields can contain junk.
// Nosplit because of the uninitialized pointer fields on the stack.
//
// The defer record must be immediately followed in memory by
// the arguments of the defer.
// Nosplit because the arguments on the stack won't be scanned
// until the defer record is spliced into the gp._defer list.
//go:nosplit
func deferprocStack(d *_defer) {
gp := getg()
@ -311,6 +313,9 @@ func newdefer() *_defer {
gp := getg()
pp := gp.m.p.ptr()
if len(pp.deferpool) == 0 && sched.deferpool != nil {
// Take the slow path on the system stack so
// we don't grow newdefer's stack.
systemstack(func() {
lock(&sched.deferlock)
for len(pp.deferpool) < cap(pp.deferpool)/2 && sched.deferpool != nil {
d := sched.deferpool
@ -319,6 +324,7 @@ func newdefer() *_defer {
pp.deferpool = append(pp.deferpool, d)
}
unlock(&sched.deferlock)
})
}
if n := len(pp.deferpool); n > 0 {
d = pp.deferpool[n-1]
@ -335,6 +341,11 @@ func newdefer() *_defer {
// Free the given defer.
// The defer cannot be used after this call.
//
// This must not grow the stack because there may be a frame without a
// stack map when this is called.
//
//go:nosplit
func freedefer(d *_defer) {
if d._panic != nil {
freedeferpanic()
@ -348,6 +359,10 @@ func freedefer(d *_defer) {
pp := getg().m.p.ptr()
if len(pp.deferpool) == cap(pp.deferpool) {
// Transfer half of local cache to the central cache.
//
// Take this slow path on the system stack so
// we don't grow freedefer's stack.
systemstack(func() {
var first, last *_defer
for len(pp.deferpool) > cap(pp.deferpool)/2 {
n := len(pp.deferpool)
@ -365,6 +380,7 @@ func freedefer(d *_defer) {
last.link = sched.deferpool
sched.deferpool = first
unlock(&sched.deferlock)
})
}
// These lines used to be simply `*d = _defer{}` but that
@ -404,6 +420,12 @@ func freedeferfn() {
// to have been called by the caller of deferreturn at the point
// just before deferreturn was called. The effect is that deferreturn
// is called again and again until there are no more deferred functions.
//
// Declared as nosplit, because the function should not be preempted once we start
// modifying the caller's frame in order to reuse the frame to call the deferred
// function.
//
//go:nosplit
func deferreturn() {
gp := getg()
d := gp._defer
@ -424,6 +446,13 @@ func deferreturn() {
return
}
// Moving arguments around.
//
// Everything called after this point must be recursively
// nosplit because the garbage collector won't know the form
// of the arguments until the jmpdefer can flip the PC over to
// fn.
argp := getcallersp() + sys.MinFrameSize
fn := d.fn
d.fn = nil
gp._defer = d.link
@ -433,9 +462,6 @@ func deferreturn() {
// called with a callback on an LR architecture and jmpdefer is on the
// stack, because jmpdefer manipulates SP (see issue #8153).
_ = **(**funcval)(unsafe.Pointer(&fn))
// We must not split the stack between computing argp and
// calling jmpdefer because argp is a uintptr stack pointer.
argp := getcallersp() + sys.MinFrameSize
jmpdefer(fn, argp)
}