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cmd/internal/obj: mark split-stack prologue nonpreemptible

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When there are both a synchronous preemption request (by
clobbering the stack guard) and an asynchronous one (by signal),
the running goroutine may observe the synchronous request first
in stack bounds check, and go to the path of calling morestack.
If the preemption signal arrives at this point before the call to
morestack, the goroutine will be asynchronously preempted,
entering the scheduler. When it is resumed, the scheduler clears
the preemption request, unclobbers the stack guard. But the
resumed goroutine will still call morestack, as it is already on
its way. morestack will, as there is no preemption request,
double the stack unnecessarily. If this happens multiple times,
the stack may grow too big, although only a small amount is
actually used.

To fix this, we mark the stack bounds check and the call to
morestack async-nonpreemptible, starting after the memory
instruction (mostly a load, on x86 CMP with memory).

Not done for Wasm as it does not support async preemption.

Fixes #35470.

Change-Id: Ibd7f3d935a3649b80f47539116ec9b9556680cf2
Reviewed-on: https://go-review.googlesource.com/c/go/+/207350
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Cherry Zhang 2019-11-14 20:23:17 -05:00
parent c3f149250e
commit b2482e4817
7 changed files with 94 additions and 40 deletions
Download patch file Download diff file Expand all files Collapse all files

17
src/cmd/internal/obj/arm/obj5.go
View file

@ -674,6 +674,12 @@ func (c *ctxt5) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R1
// Mark the stack bound check and morestack call async nonpreemptible.
// If we get preempted here, when resumed the preemption request is
// cleared, but we'll still call morestack, which will double the stack
// unnecessarily. See issue #35470.
p = c.ctxt.StartUnsafePoint(p, c.newprog)
if framesize <= objabi.StackSmall {
// small stack: SP < stackguard
// CMP stackguard, SP
@ -757,6 +763,8 @@ func (c *ctxt5) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
bls.As = ABLS
bls.To.Type = obj.TYPE_BRANCH
end := c.ctxt.EndUnsafePoint(bls, c.newprog, -1)
var last *obj.Prog
for last = c.cursym.Func.Text; last.Link != nil; last = last.Link {
}
@ -768,7 +776,8 @@ func (c *ctxt5) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
spfix.As = obj.ANOP
spfix.Spadj = -framesize
pcdata := c.ctxt.EmitEntryLiveness(c.cursym, spfix, c.newprog)
pcdata := c.ctxt.EmitEntryStackMap(c.cursym, spfix, c.newprog)
pcdata = c.ctxt.StartUnsafePoint(pcdata, c.newprog)
// MOVW LR, R3
movw := obj.Appendp(pcdata, c.newprog)
@ -793,14 +802,16 @@ func (c *ctxt5) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
}
call.To.Sym = c.ctxt.Lookup(morestack)
pcdata = c.ctxt.EndUnsafePoint(call, c.newprog, -1)
// B start
b := obj.Appendp(call, c.newprog)
b := obj.Appendp(pcdata, c.newprog)
b.As = obj.AJMP
b.To.Type = obj.TYPE_BRANCH
b.Pcond = c.cursym.Func.Text.Link
b.Spadj = +framesize
return bls
return end
}
var unaryDst = map[obj.As]bool{

21
src/cmd/internal/obj/arm64/obj7.go
View file

@ -62,6 +62,12 @@ func (c *ctxt7) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R1
// Mark the stack bound check and morestack call async nonpreemptible.
// If we get preempted here, when resumed the preemption request is
// cleared, but we'll still call morestack, which will double the stack
// unnecessarily. See issue #35470.
p = c.ctxt.StartUnsafePoint(p, c.newprog)
q := (*obj.Prog)(nil)
if framesize <= objabi.StackSmall {
// small stack: SP < stackguard
@ -156,6 +162,8 @@ func (c *ctxt7) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
bls.As = ABLS
bls.To.Type = obj.TYPE_BRANCH
end := c.ctxt.EndUnsafePoint(bls, c.newprog, -1)
var last *obj.Prog
for last = c.cursym.Func.Text; last.Link != nil; last = last.Link {
}
@ -167,7 +175,8 @@ func (c *ctxt7) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
spfix.As = obj.ANOP
spfix.Spadj = -framesize
pcdata := c.ctxt.EmitEntryLiveness(c.cursym, spfix, c.newprog)
pcdata := c.ctxt.EmitEntryStackMap(c.cursym, spfix, c.newprog)
pcdata = c.ctxt.StartUnsafePoint(pcdata, c.newprog)
// MOV LR, R3
movlr := obj.Appendp(pcdata, c.newprog)
@ -204,18 +213,16 @@ func (c *ctxt7) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
}
call.To.Sym = c.ctxt.Lookup(morestack)
pcdata = c.ctxt.EndUnsafePoint(call, c.newprog, -1)
// B start
jmp := obj.Appendp(call, c.newprog)
jmp := obj.Appendp(pcdata, c.newprog)
jmp.As = AB
jmp.To.Type = obj.TYPE_BRANCH
jmp.Pcond = c.cursym.Func.Text.Link
jmp.Spadj = +framesize
// placeholder for bls's jump target
// p = obj.Appendp(ctxt, p)
// p.As = obj.ANOP
return bls
return end
}
func progedit(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc) {

10
src/cmd/internal/obj/mips/obj0.go
View file

@ -677,6 +677,12 @@ func (c *ctxt0) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R1
// Mark the stack bound check and morestack call async nonpreemptible.
// If we get preempted here, when resumed the preemption request is
// cleared, but we'll still call morestack, which will double the stack
// unnecessarily. See issue #35470.
p = c.ctxt.StartUnsafePoint(p, c.newprog)
var q *obj.Prog
if framesize <= objabi.StackSmall {
// small stack: SP < stackguard
@ -796,7 +802,7 @@ func (c *ctxt0) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
p.Mark |= LABEL
}
p = c.ctxt.EmitEntryLiveness(c.cursym, p, c.newprog)
p = c.ctxt.EmitEntryStackMap(c.cursym, p, c.newprog)
// JAL runtime.morestack(SB)
p = obj.Appendp(p, c.newprog)
@ -812,6 +818,8 @@ func (c *ctxt0) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
}
p.Mark |= BRANCH
p = c.ctxt.EndUnsafePoint(p, c.newprog, -1)
// JMP start
p = obj.Appendp(p, c.newprog)

15
src/cmd/internal/obj/plist.go
View file

@ -187,6 +187,13 @@ func (ctxt *Link) Globl(s *LSym, size int64, flag int) {
// liveness map active at the entry of function s. It returns the last
// Prog generated.
func (ctxt *Link) EmitEntryLiveness(s *LSym, p *Prog, newprog ProgAlloc) *Prog {
pcdata := ctxt.EmitEntryStackMap(s, p, newprog)
pcdata = ctxt.EmitEntryRegMap(s, pcdata, newprog)
return pcdata
}
// Similar to EmitEntryLiveness, but just emit stack map.
func (ctxt *Link) EmitEntryStackMap(s *LSym, p *Prog, newprog ProgAlloc) *Prog {
pcdata := Appendp(p, newprog)
pcdata.Pos = s.Func.Text.Pos
pcdata.As = APCDATA
@ -195,8 +202,12 @@ func (ctxt *Link) EmitEntryLiveness(s *LSym, p *Prog, newprog ProgAlloc) *Prog {
pcdata.To.Type = TYPE_CONST
pcdata.To.Offset = -1 // pcdata starts at -1 at function entry
// Same, with register map.
pcdata = Appendp(pcdata, newprog)
return pcdata
}
// Similar to EmitEntryLiveness, but just emit register map.
func (ctxt *Link) EmitEntryRegMap(s *LSym, p *Prog, newprog ProgAlloc) *Prog {
pcdata := Appendp(p, newprog)
pcdata.Pos = s.Func.Text.Pos
pcdata.As = APCDATA
pcdata.From.Type = TYPE_CONST

10
src/cmd/internal/obj/ppc64/obj9.go
View file

@ -1045,6 +1045,12 @@ func (c *ctxt9) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R3
// Mark the stack bound check and morestack call async nonpreemptible.
// If we get preempted here, when resumed the preemption request is
// cleared, but we'll still call morestack, which will double the stack
// unnecessarily. See issue #35470.
p = c.ctxt.StartUnsafePoint(p, c.newprog)
var q *obj.Prog
if framesize <= objabi.StackSmall {
// small stack: SP < stackguard
@ -1153,7 +1159,7 @@ func (c *ctxt9) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
q.Pcond = p
}
p = c.ctxt.EmitEntryLiveness(c.cursym, p, c.newprog)
p = c.ctxt.EmitEntryStackMap(c.cursym, p, c.newprog)
var morestacksym *obj.LSym
if c.cursym.CFunc() {
@ -1239,6 +1245,8 @@ func (c *ctxt9) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
p.To.Reg = REG_R2
}
p = c.ctxt.EndUnsafePoint(p, c.newprog, -1)
// BR start
p = obj.Appendp(p, c.newprog)
p.As = ABR

34
src/cmd/internal/obj/s390x/objz.go
View file

@ -335,6 +335,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
if !p.From.Sym.NoSplit() {
p, pPreempt = c.stacksplitPre(p, autosize) // emit pre part of split check
pPre = p
p = c.ctxt.EndUnsafePoint(p, c.newprog, -1)
wasSplit = true //need post part of split
}
@ -575,15 +576,16 @@ func (c *ctxtz) stacksplitPre(p *obj.Prog, framesize int32) (*obj.Prog, *obj.Pro
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R3
// Mark the stack bound check and morestack call async nonpreemptible.
// If we get preempted here, when resumed the preemption request is
// cleared, but we'll still call morestack, which will double the stack
// unnecessarily. See issue #35470.
p = c.ctxt.StartUnsafePoint(p, c.newprog)
q = nil
if framesize <= objabi.StackSmall {
// small stack: SP < stackguard
// CMP stackguard, SP
//p.To.Type = obj.TYPE_REG
//p.To.Reg = REGSP
// q1: BLT done
// CMPUBGE stackguard, SP, label-of-call-to-morestack
p = obj.Appendp(p, c.newprog)
//q1 = p
@ -592,22 +594,11 @@ func (c *ctxtz) stacksplitPre(p *obj.Prog, framesize int32) (*obj.Prog, *obj.Pro
p.Reg = REGSP
p.As = ACMPUBGE
p.To.Type = obj.TYPE_BRANCH
//p = obj.Appendp(ctxt, p)
//p.As = ACMPU
//p.From.Type = obj.TYPE_REG
//p.From.Reg = REG_R3
//p.To.Type = obj.TYPE_REG
//p.To.Reg = REGSP
//p = obj.Appendp(ctxt, p)
//p.As = ABGE
//p.To.Type = obj.TYPE_BRANCH
} else if framesize <= objabi.StackBig {
// large stack: SP-framesize < stackguard-StackSmall
// ADD $-(framesize-StackSmall), SP, R4
// CMP stackguard, R4
// CMPUBGE stackguard, R4, label-of-call-to-morestack
p = obj.Appendp(p, c.newprog)
p.As = AADD
@ -639,7 +630,7 @@ func (c *ctxtz) stacksplitPre(p *obj.Prog, framesize int32) (*obj.Prog, *obj.Pro
// ADD $StackGuard, SP, R4
// SUB R3, R4
// MOVD $(framesize+(StackGuard-StackSmall)), TEMP
// CMPUBGE TEMP, R4
// CMPUBGE TEMP, R4, label-of-call-to-morestack
p = obj.Appendp(p, c.newprog)
p.As = ACMP
@ -694,7 +685,8 @@ func (c *ctxtz) stacksplitPost(p *obj.Prog, pPre *obj.Prog, pPreempt *obj.Prog,
spfix.As = obj.ANOP
spfix.Spadj = -framesize
pcdata := c.ctxt.EmitEntryLiveness(c.cursym, spfix, c.newprog)
pcdata := c.ctxt.EmitEntryStackMap(c.cursym, spfix, c.newprog)
pcdata = c.ctxt.StartUnsafePoint(pcdata, c.newprog)
// MOVD LR, R5
p = obj.Appendp(pcdata, c.newprog)
@ -721,6 +713,8 @@ func (c *ctxtz) stacksplitPost(p *obj.Prog, pPre *obj.Prog, pPreempt *obj.Prog,
p.To.Sym = c.ctxt.Lookup("runtime.morestack")
}
p = c.ctxt.EndUnsafePoint(p, c.newprog, -1)
// BR start
p = obj.Appendp(p, c.newprog)

27
src/cmd/internal/obj/x86/obj6.go
View file

@ -998,6 +998,12 @@ func stacksplit(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog, newprog obj.ProgA
if cursym.CFunc() {
p.To.Offset = 3 * int64(ctxt.Arch.PtrSize) // G.stackguard1
}
// Mark the stack bound check and morestack call async nonpreemptible.
// If we get preempted here, when resumed the preemption request is
// cleared, but we'll still call morestack, which will double the stack
// unnecessarily. See issue #35470.
p = ctxt.StartUnsafePoint(p, newprog)
} else if framesize <= objabi.StackBig {
// large stack: SP-framesize <= stackguard-StackSmall
// LEAQ -xxx(SP), AX
@ -1020,6 +1026,8 @@ func stacksplit(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog, newprog obj.ProgA
if cursym.CFunc() {
p.To.Offset = 3 * int64(ctxt.Arch.PtrSize) // G.stackguard1
}
p = ctxt.StartUnsafePoint(p, newprog) // see the comment above
} else {
// Such a large stack we need to protect against wraparound.
// If SP is close to zero:
@ -1029,11 +1037,11 @@ func stacksplit(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog, newprog obj.ProgA
//
// Preemption sets stackguard to StackPreempt, a very large value.
// That breaks the math above, so we have to check for that explicitly.
// MOVQ stackguard, CX
// CMPQ CX, $StackPreempt
// MOVQ stackguard, SI
// CMPQ SI, $StackPreempt
// JEQ label-of-call-to-morestack
// LEAQ StackGuard(SP), AX
// SUBQ CX, AX
// SUBQ SI, AX
// CMPQ AX, $(framesize+(StackGuard-StackSmall))
p = obj.Appendp(p, newprog)
@ -1047,6 +1055,8 @@ func stacksplit(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog, newprog obj.ProgA
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_SI
p = ctxt.StartUnsafePoint(p, newprog) // see the comment above
p = obj.Appendp(p, newprog)
p.As = cmp
p.From.Type = obj.TYPE_REG
@ -1090,6 +1100,8 @@ func stacksplit(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog, newprog obj.ProgA
jls.As = AJLS
jls.To.Type = obj.TYPE_BRANCH
end := ctxt.EndUnsafePoint(jls, newprog, -1)
var last *obj.Prog
for last = cursym.Func.Text; last.Link != nil; last = last.Link {
}
@ -1101,7 +1113,8 @@ func stacksplit(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog, newprog obj.ProgA
spfix.As = obj.ANOP
spfix.Spadj = -framesize
pcdata := ctxt.EmitEntryLiveness(cursym, spfix, newprog)
pcdata := ctxt.EmitEntryStackMap(cursym, spfix, newprog)
pcdata = ctxt.StartUnsafePoint(pcdata, newprog)
call := obj.Appendp(pcdata, newprog)
call.Pos = cursym.Func.Text.Pos
@ -1126,7 +1139,9 @@ func stacksplit(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog, newprog obj.ProgA
progedit(ctxt, callend.Link, newprog)
}
jmp := obj.Appendp(callend, newprog)
pcdata = ctxt.EndUnsafePoint(callend, newprog, -1)
jmp := obj.Appendp(pcdata, newprog)
jmp.As = obj.AJMP
jmp.To.Type = obj.TYPE_BRANCH
jmp.Pcond = cursym.Func.Text.Link
@ -1137,7 +1152,7 @@ func stacksplit(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog, newprog obj.ProgA
q1.Pcond = call
}
return jls
return end
}
var unaryDst = map[obj.As]bool{