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runtime: fix the potential race of idle P's during injectglist

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Fixes #63555

Change-Id: I26e7baf58fcb78e66e0feed5725e371e25d657cc
Reviewed-on: https://go-review.googlesource.com/c/go/+/550175
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
This commit is contained in:
Andy Pan 2023-12-15 17:19:08 +08:00 committed by Michael Pratt
parent 234390e741
commit 24070cf747
1 changed files with 19 additions and 2 deletions
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21
src/runtime/proc.go
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@ -3816,8 +3816,10 @@ func injectglist(glist *gList) {
}
npidle := int(sched.npidle.Load())
var globq gQueue
var n int
var (
globq gQueue
n int
)
for n = 0; n < npidle && !q.empty(); n++ {
g := q.pop()
globq.pushBack(g)
@ -3833,6 +3835,21 @@ func injectglist(glist *gList) {
if !q.empty() {
runqputbatch(pp, &q, qsize)
}
// Some P's might have become idle after we loaded `sched.npidle`
// but before any goroutines were added to the queue, which could
// lead to idle P's when there is work available in the global queue.
// That could potentially last until other goroutines become ready
// to run. That said, we need to find a way to hedge
//
// Calling wakep() here is the best bet, it will do nothing in the
// common case (no racing on `sched.npidle`), while it could wake one
// more P to execute G's, which might end up with >1 P's: the first one
// wakes another P and so forth until there is no more work, but this
// ought to be an extremely rare case.
//
// Also see "Worker thread parking/unparking" comment at the top of the file for details.
wakep()
}
// One round of scheduler: find a runnable goroutine and execute it.