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runtime: fix stackCache=0 debug mode

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Setting stackCache to 0 to disable stack caches for debugging hasn't
worked for a long time. It causes stackalloc to fall back to full span
allocation, round sub-page stacks down to 0 pages, and blow up.

Fix this debug mode so it disables the per-P caches, but continues to
use the global stack pools for small stacks, which correctly handle
sub-page stacks. While we're here, rename stackCache to stackNoCache
so it acts like the rest of the stack allocator debug modes where "0"
is the right default value.

Fixes #17291.

Change-Id: If401c41cee3448513cbd7bb2e9334a8efab257a7
Reviewed-on: https://go-review.googlesource.com/43637
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Austin Clements 2017-05-18 14:35:53 -04:00
parent 8a1c5b2e48
commit 475425201a
1 changed files with 5 additions and 6 deletions
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11
src/runtime/stack.go
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@ -121,8 +121,7 @@ const (
stackFromSystem = 0 // allocate stacks from system memory instead of the heap
stackFaultOnFree = 0 // old stacks are mapped noaccess to detect use after free
stackPoisonCopy = 0 // fill stack that should not be accessed with garbage, to detect bad dereferences during copy
stackCache = 1
stackNoCache = 0 // disable per-P small stack caches
// check the BP links during traceback.
debugCheckBP = false
@ -349,7 +348,7 @@ func stackalloc(n uint32) stack {
// If we need a stack of a bigger size, we fall back on allocating
// a dedicated span.
var v unsafe.Pointer
if stackCache != 0 && n < _FixedStack<<_NumStackOrders && n < _StackCacheSize {
if n < _FixedStack<<_NumStackOrders && n < _StackCacheSize {
order := uint8(0)
n2 := n
for n2 > _FixedStack {
@ -358,7 +357,7 @@ func stackalloc(n uint32) stack {
}
var x gclinkptr
c := thisg.m.mcache
if c == nil || thisg.m.preemptoff != "" || thisg.m.helpgc != 0 {
if stackNoCache != 0 || c == nil || thisg.m.preemptoff != "" || thisg.m.helpgc != 0 {
// c == nil can happen in the guts of exitsyscall or
// procresize. Just get a stack from the global pool.
// Also don't touch stackcache during gc
@ -443,7 +442,7 @@ func stackfree(stk stack) {
if msanenabled {
msanfree(v, n)
}
if stackCache != 0 && n < _FixedStack<<_NumStackOrders && n < _StackCacheSize {
if n < _FixedStack<<_NumStackOrders && n < _StackCacheSize {
order := uint8(0)
n2 := n
for n2 > _FixedStack {
@ -452,7 +451,7 @@ func stackfree(stk stack) {
}
x := gclinkptr(v)
c := gp.m.mcache
if c == nil || gp.m.preemptoff != "" || gp.m.helpgc != 0 {
if stackNoCache != 0 || c == nil || gp.m.preemptoff != "" || gp.m.helpgc != 0 {
lock(&stackpoolmu)
stackpoolfree(x, order)
unlock(&stackpoolmu)