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[dev.typeparams] Revert "[dev.typeparams] runtime: remove unnecessary split-prevention from defer code"
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
parent
e3e9f0bb2d
commit
7bed50e667
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@ -261,8 +261,10 @@ func deferproc(fn func()) {
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// deferprocStack queues a new deferred function with a defer record on the stack.
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// The defer record must have its fn field initialized.
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// All other fields can contain junk.
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// Nosplit because of the uninitialized pointer fields on the stack.
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//
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// The defer record must be immediately followed in memory by
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// the arguments of the defer.
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// Nosplit because the arguments on the stack won't be scanned
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// until the defer record is spliced into the gp._defer list.
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//go:nosplit
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func deferprocStack(d *_defer) {
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gp := getg()
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@ -311,14 +313,18 @@ func newdefer() *_defer {
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gp := getg()
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pp := gp.m.p.ptr()
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if len(pp.deferpool) == 0 && sched.deferpool != nil {
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lock(&sched.deferlock)
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for len(pp.deferpool) < cap(pp.deferpool)/2 && sched.deferpool != nil {
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d := sched.deferpool
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sched.deferpool = d.link
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d.link = nil
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pp.deferpool = append(pp.deferpool, d)
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}
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unlock(&sched.deferlock)
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// Take the slow path on the system stack so
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// we don't grow newdefer's stack.
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systemstack(func() {
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lock(&sched.deferlock)
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for len(pp.deferpool) < cap(pp.deferpool)/2 && sched.deferpool != nil {
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d := sched.deferpool
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sched.deferpool = d.link
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d.link = nil
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pp.deferpool = append(pp.deferpool, d)
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}
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unlock(&sched.deferlock)
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})
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}
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if n := len(pp.deferpool); n > 0 {
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d = pp.deferpool[n-1]
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@ -335,6 +341,11 @@ func newdefer() *_defer {
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// Free the given defer.
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// The defer cannot be used after this call.
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//
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// This must not grow the stack because there may be a frame without a
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// stack map when this is called.
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//
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//go:nosplit
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func freedefer(d *_defer) {
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if d._panic != nil {
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freedeferpanic()
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@ -348,23 +359,28 @@ func freedefer(d *_defer) {
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pp := getg().m.p.ptr()
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if len(pp.deferpool) == cap(pp.deferpool) {
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// Transfer half of local cache to the central cache.
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var first, last *_defer
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for len(pp.deferpool) > cap(pp.deferpool)/2 {
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n := len(pp.deferpool)
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d := pp.deferpool[n-1]
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pp.deferpool[n-1] = nil
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pp.deferpool = pp.deferpool[:n-1]
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if first == nil {
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first = d
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} else {
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last.link = d
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//
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// Take this slow path on the system stack so
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// we don't grow freedefer's stack.
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systemstack(func() {
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var first, last *_defer
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for len(pp.deferpool) > cap(pp.deferpool)/2 {
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n := len(pp.deferpool)
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d := pp.deferpool[n-1]
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pp.deferpool[n-1] = nil
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pp.deferpool = pp.deferpool[:n-1]
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if first == nil {
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first = d
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} else {
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last.link = d
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}
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last = d
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}
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last = d
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}
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lock(&sched.deferlock)
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last.link = sched.deferpool
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sched.deferpool = first
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unlock(&sched.deferlock)
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lock(&sched.deferlock)
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last.link = sched.deferpool
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sched.deferpool = first
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unlock(&sched.deferlock)
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})
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}
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// These lines used to be simply `*d = _defer{}` but that
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@ -404,6 +420,12 @@ func freedeferfn() {
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// to have been called by the caller of deferreturn at the point
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// just before deferreturn was called. The effect is that deferreturn
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// is called again and again until there are no more deferred functions.
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//
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// Declared as nosplit, because the function should not be preempted once we start
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// modifying the caller's frame in order to reuse the frame to call the deferred
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// function.
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//
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//go:nosplit
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func deferreturn() {
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gp := getg()
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d := gp._defer
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@ -424,6 +446,13 @@ func deferreturn() {
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return
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}
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// Moving arguments around.
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//
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// Everything called after this point must be recursively
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// nosplit because the garbage collector won't know the form
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// of the arguments until the jmpdefer can flip the PC over to
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// fn.
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argp := getcallersp() + sys.MinFrameSize
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fn := d.fn
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d.fn = nil
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gp._defer = d.link
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@ -433,9 +462,6 @@ func deferreturn() {
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// called with a callback on an LR architecture and jmpdefer is on the
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// stack, because jmpdefer manipulates SP (see issue #8153).
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_ = **(**funcval)(unsafe.Pointer(&fn))
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// We must not split the stack between computing argp and
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// calling jmpdefer because argp is a uintptr stack pointer.
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argp := getcallersp() + sys.MinFrameSize
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jmpdefer(fn, argp)
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}
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