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runtime: make gcFlushBgCredit go:nowritebarrierrec

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Write barriers in gcFlushBgCredit lead to very subtle bugs because it
executes after the getfull barrier. I tracked some bugs of this form
down before go:nowritebarrierrec was implemented. Ensure that they
don't reappear by making gcFlushBgCredit go:nowritebarrierrec.

Change-Id: Ia5ca2dc59e6268bce8d8b4c87055bd0f6e19bed2
Reviewed-on: https://go-review.googlesource.com/17052
Reviewed-by: Russ Cox <rsc@golang.org>
This commit is contained in:
Austin Clements 2015-11-19 11:25:55 -05:00
parent e126f30a66
commit ab9d5f38be
1 changed files with 10 additions and 0 deletions
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10
src/runtime/mgcmark.go
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@ -504,6 +504,12 @@ func gcWakeAllAssists() {
// credit. This first satisfies blocked assists on the
// work.assistQueue and then flushes any remaining credit to
// gcController.bgScanCredit.
//
// Write barriers are disallowed because this is used by gcDrain after
// it has ensured that all work is drained and this must preserve that
// condition.
//
//go:nowritebarrierrec
func gcFlushBgCredit(scanWork int64) {
if work.assistQueue.head == 0 {
// Fast path; there are no blocked assists. There's a
@ -846,6 +852,10 @@ func gcDrain(gcw *gcWork, flags gcDrainFlags) {
}
}
// In blocking mode, write barriers are not allowed after this
// point because we must preserve the condition that the work
// buffers are empty.
// Flush remaining scan work credit.
if gcw.scanWork > 0 {
atomic.Xaddint64(&gcController.scanWork, gcw.scanWork)