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runtime: disallow malloc or panic in scavenge

Mallocs and panics in the scavenge path are particularly nasty because
they're likely to silently self-deadlock on the mheap.lock. Avoid
sinking lots of time into debugging these issues in the future by
turning these into immediate throws.

Change-Id: Ib36fdda33bc90b21c32432b03561630c1f3c69bc
Reviewed-on: https://go-review.googlesource.com/38293
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>
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aclements committed Mar 16, 2017
1 parent 13ae271 commit df6025bc0d7746fdf40a39398e5d8799ccf78a55
Showing with 6 additions and 0 deletions.
  1. +6 −0 src/runtime/mheap.go
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@@ -991,13 +991,19 @@ func scavengelist(list *mSpanList, now, limit uint64) uintptr {
}
func (h *mheap) scavenge(k int32, now, limit uint64) {
// Disallow malloc or panic while holding the heap lock. We do
// this here because this is an non-mallocgc entry-point to
// the mheap API.
gp := getg()
gp.m.mallocing++
lock(&h.lock)
var sumreleased uintptr
for i := 0; i < len(h.free); i++ {
sumreleased += scavengelist(&h.free[i], now, limit)
}
sumreleased += scavengelist(&h.freelarge, now, limit)
unlock(&h.lock)
gp.m.mallocing--
if debug.gctrace > 0 {
if sumreleased > 0 {

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