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runtime: copy stack before adjusting

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Currently copystack adjusts pointers in the old stack and then copies
the adjusted stack to the new stack. In addition to being generally
confusing, this is going to make concurrent stack shrinking harder.

Switch this around so that we first copy the stack and then adjust
pointers on the new stack (never writing to the old stack).

This reprises CL 15996, but takes a different and simpler approach. CL
15996 still walked the old stack while adjusting pointers on the new
stack. In this CL, we adjust auxiliary structures before walking the
stack, so we can just walk the new stack.

For #12967.

Change-Id: I94fa86f823ba9ee478e73b2ba509eed3361c43df
Reviewed-on: https://go-review.googlesource.com/20033
Reviewed-by: Rick Hudson <rlh@golang.org>
This commit is contained in:
Austin Clements 2016-02-16 12:23:33 -05:00
parent 5a50e00306
commit da153354b2
1 changed files with 14 additions and 13 deletions
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27
src/runtime/stack.go
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@ -748,29 +748,27 @@ func copystack(gp *g, newsize uintptr) {
print("copystack gp=", gp, " [", hex(old.lo), " ", hex(old.hi-used), " ", hex(old.hi), "]/", gp.stackAlloc, " -> [", hex(new.lo), " ", hex(new.hi-used), " ", hex(new.hi), "]/", newsize, "\n")
}
// Compute adjustment.
var adjinfo adjustinfo
adjinfo.old = old
adjinfo.delta = new.hi - old.hi
// copy the stack to the new location
memmove(unsafe.Pointer(new.hi-used), unsafe.Pointer(old.hi-used), used)
// Disallow sigprof scans of this stack and block if there's
// one in progress.
gcLockStackBarriers(gp)
// adjust pointers in the to-be-copied frames
var adjinfo adjustinfo
adjinfo.old = old
adjinfo.delta = new.hi - old.hi
gentraceback(^uintptr(0), ^uintptr(0), 0, gp, 0, nil, 0x7fffffff, adjustframe, noescape(unsafe.Pointer(&adjinfo)), 0)
// adjust other miscellaneous things that have pointers into stacks.
// Adjust structures that have pointers into stacks. We have
// to do most of these before we traceback the new stack
// because gentraceback uses them.
adjustctxt(gp, &adjinfo)
adjustdefers(gp, &adjinfo)
adjustpanics(gp, &adjinfo)
adjustsudogs(gp, &adjinfo)
adjuststkbar(gp, &adjinfo)
// copy the stack to the new location
if stackPoisonCopy != 0 {
fillstack(new, 0xfb)
}
memmove(unsafe.Pointer(new.hi-used), unsafe.Pointer(old.hi-used), used)
// copy old stack barriers to new stack barrier array
newstkbar = newstkbar[:len(gp.stkbar)]
copy(newstkbar, gp.stkbar)
@ -784,6 +782,9 @@ func copystack(gp *g, newsize uintptr) {
gp.stkbar = newstkbar
gp.stktopsp += adjinfo.delta
// Adjust pointers in the new stack.
gentraceback(^uintptr(0), ^uintptr(0), 0, gp, 0, nil, 0x7fffffff, adjustframe, noescape(unsafe.Pointer(&adjinfo)), 0)
gcUnlockStackBarriers(gp)
// free old stack