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[release-20.0] Fix potential deadlock in health streamer (#17261) #17269

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Nov 21, 2024
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[release-20.0] Fix potential deadlock in health streamer (#17261) #17269

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4 changes: 3 additions & 1 deletion go/vt/vttablet/tabletserver/health_streamer.go
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Original file line number Diff line number Diff line change
Expand Up @@ -317,8 +317,10 @@ func (hs *healthStreamer) SetUnhealthyThreshold(v time.Duration) {
// so it can read and write to the MySQL instance for schema-tracking.
func (hs *healthStreamer) MakePrimary(serving bool) {
hs.fieldsMu.Lock()
defer hs.fieldsMu.Unlock()
hs.isServingPrimary = serving
// We let go of the lock here because we don't want to hold the lock when calling RegisterNotifier.
// If we keep holding the lock, there is a potential deadlock that can happen.
hs.fieldsMu.Unlock()
// We register for notifications from the schema Engine only when schema tracking is enabled,
// and we are going to a serving primary state.
if serving && hs.signalWhenSchemaChange {
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3 changes: 2 additions & 1 deletion go/vt/vttablet/tabletserver/health_streamer_test.go
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Expand Up @@ -589,13 +589,14 @@ func TestDeadlockBwCloseAndReload(t *testing.T) {

wg := sync.WaitGroup{}
wg.Add(2)
// Try running Close and reload in parallel multiple times.
// Try running Close & MakePrimary and reload in parallel multiple times.
// This reproduces the deadlock quite readily.
go func() {
defer wg.Done()
for i := 0; i < 100; i++ {
hs.Close()
hs.Open()
hs.MakePrimary(true)
}
}()

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