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runtime: don't send preemption signal if there is a signal pending

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If multiple threads call preemptone to preempt the same M, it may
send many signals to the same M such that it hardly make
progress, causing live-lock problem. Only send a signal if there
isn't already one pending.

Fixes #37741.

Change-Id: Id94adb0b95acbd18b23abe637a8dcd81ab41b452
Reviewed-on: https://go-review.googlesource.com/c/go/+/223737
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Cherry Zhang 2020-03-16 20:08:00 -04:00
parent 6412750f32
commit 0c0e8f224d
2 changed files with 13 additions and 1 deletions
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4
src/runtime/runtime2.go
View File

@ -539,6 +539,10 @@ type m struct {
// requested, but fails. Accessed atomically.
preemptGen uint32
// Whether this is a pending preemption signal on this M.
// Accessed atomically.
signalPending uint32
dlogPerM
mOS

10
src/runtime/signal_unix.go
View File

@ -333,6 +333,7 @@ func doSigPreempt(gp *g, ctxt *sigctxt) {
// Acknowledge the preemption.
atomic.Xadd(&gp.m.preemptGen, 1)
atomic.Store(&gp.m.signalPending, 0)
}
const preemptMSupported = pushCallSupported
@ -359,7 +360,14 @@ func preemptM(mp *m) {
// required).
return
}
signalM(mp, sigPreempt)
if atomic.Cas(&mp.signalPending, 0, 1) {
// If multiple threads are preempting the same M, it may send many
// signals to the same M such that it hardly make progress, causing
// live-lock problem. Apparently this could happen on darwin. See
// issue #37741.
// Only send a signal if there isn't already one pending.
signalM(mp, sigPreempt)
}
}
// sigFetchG fetches the value of G safely when running in a signal handler.