From d70b0fe6c4d1b1369b742ea5b7d4e6f0c50ffdcb Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Fri, 28 Oct 2016 11:14:07 -0400 Subject: [PATCH] runtime: fix preemption of root marking jobs The current logic in gcDrain conflates non-blocking with preemptible draining for root jobs. As a result, if you do a non-blocking (but *not* preemptible) drain, like dedicated workers do, the root job drain will stop if preempted and fall through to heap marking jobs, which won't stop until it fails to get a heap marking job. This commit fixes the condition on root marking jobs so they only stop when preempted if the drain is preemptible. Coincidentally, this also fixes a nil pointer dereference if we call gcDrain with gcDrainNoBlock and without a user G, since it tries to get the preempt flag from the nil user G. This combination never happens right now, but will in the future. Change-Id: Ia910ec20a9b46237f7926969144a33b1b4a7b2f9 Reviewed-on: https://go-review.googlesource.com/32291 Run-TryBot: Austin Clements TryBot-Result: Gobot Gobot Reviewed-by: Russ Cox --- src/runtime/mgcmark.go | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go index 286aeb74a9..7819698def 100644 --- a/src/runtime/mgcmark.go +++ b/src/runtime/mgcmark.go @@ -973,7 +973,7 @@ func gcDrain(gcw *gcWork, flags gcDrainFlags) { // Drain root marking jobs. if work.markrootNext < work.markrootJobs { - for blocking || !gp.preempt { + for !(preemptible && gp.preempt) { job := atomic.Xadd(&work.markrootNext, +1) - 1 if job >= work.markrootJobs { break