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runtime: set G wait reason more consistently

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Currently, wait reasons are set somewhat inconsistently. In a follow-up
CL, we're going to want to rely on the wait reason being there for
casgstatus, so the status quo isn't really going to work for that. Plus
this inconsistency means there are a whole bunch of cases where we could
be more specific about the G's status but aren't.

So, this change adds a new function, casGToWaiting which is like
casgstatus but also sets the wait reason. The goal is that by using this
API it'll be harder to forget to set a wait reason (or the lack thereof
will at least be explicit). This change then updates all casgstatus(gp,
..., _Gwaiting) calls to casGToWaiting(gp, ..., waitReasonX) instead.
For a number of these cases, we're missing a wait reason, and it
wouldn't hurt to add a wait reason for them, so this change also adds
those wait reasons.

For #49881.

Change-Id: Ia95e06ecb74ed17bb7bb94f1a362ebfe6bec1518
Reviewed-on: https://go-review.googlesource.com/c/go/+/427617
Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
This commit is contained in:
Michael Anthony Knyszek 2022-08-31 18:21:48 +00:00 • committed by Gopher Robot
parent a2c396ce00
commit 686b38b5b2
6 changed files with 27 additions and 15 deletions
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17
src/runtime/proc.go
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@ -1027,6 +1027,14 @@ func casgstatus(gp *g, oldval, newval uint32) {
}
}
// casGToWaiting transitions gp from old to _Gwaiting, and sets the wait reason.
//
// Use this over casgstatus when possible to ensure that a waitreason is set.
func casGToWaiting(gp *g, old uint32, reason waitReason) {
gp.waitreason = reason
casgstatus(gp, old, _Gwaiting)
}
// casgstatus(gp, oldstatus, Gcopystack), assuming oldstatus is Gwaiting or Grunnable.
// Returns old status. Cannot call casgstatus directly, because we are racing with an
// async wakeup that might come in from netpoll. If we see Gwaiting from the readgstatus,
@ -1066,6 +1074,7 @@ func casGFromPreempted(gp *g, old, new uint32) bool {
if old != _Gpreempted || new != _Gwaiting {
throw("bad g transition")
}
gp.waitreason = waitReasonPreempted
return gp.atomicstatus.CompareAndSwap(_Gpreempted, _Gwaiting)
}
@ -1098,7 +1107,8 @@ func stopTheWorld(reason string) {
// must have preempted all goroutines, including any attempting
// to scan our stack, in which case, any stack shrinking will
// have already completed by the time we exit.
casgstatus(gp, _Grunning, _Gwaiting)
// Don't provide a wait reason because we're still executing.
casGToWaiting(gp, _Grunning, waitReasonStoppingTheWorld)
stopTheWorldWithSema()
casgstatus(gp, _Gwaiting, _Grunning)
})
@ -3395,6 +3405,8 @@ func park_m(gp *g) {
traceGoPark(mp.waittraceev, mp.waittraceskip)
}
// N.B. Not using casGToWaiting here because the waitreason is
// set by park_m's caller.
casgstatus(gp, _Grunning, _Gwaiting)
dropg()
@ -3468,7 +3480,6 @@ func preemptPark(gp *g) {
dumpgstatus(gp)
throw("bad g status")
}
gp.waitreason = waitReasonPreempted
if gp.asyncSafePoint {
// Double-check that async preemption does not
@ -3545,7 +3556,7 @@ func goexit0(gp *g) {
gp._defer = nil // should be true already but just in case.
gp._panic = nil // non-nil for Goexit during panic. points at stack-allocated data.
gp.writebuf = nil
gp.waitreason = 0
gp.waitreason = waitReasonZero
gp.param = nil
gp.labels = nil
gp.timer = nil