cache: don't let RowByModel() recursively lock the RowCache #270
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RWLocks are not supposed to be used recursively, and if something else Locks the row cache then we deadlock. In this example, goroutine 59 RLocks the RowCache, and then goroutine 174 attempts to Lock the cache but blocks on ovn-org#59's RLock. Since there is a writer waiting to acquire the lock, any further RLocks are effectively Locks, and thus when goroutine ovn-org#59 attempts to acquire the second RLock in Row() it deadlocks against goroutine ovn-org#174. goroutine 59 [semacquire, 12 minutes]: sync.runtime_SemacquireMutex(0xc000bf2e2c, 0xc0025a3800, 0x0) /usr/lib/golang/src/runtime/sema.go:71 +0x47 sync.(*RWMutex).RLock(...) /usr/lib/golang/src/sync/rwmutex.go:63 github.com/ovn-org/libovsdb/cache.(*RowCache).Row(0xc000bf2d80, 0xc00342de60, 0x24, 0x0, 0x0) /go/src/github.com/openshift/ovn-kubernetes/go-controller/vendor/github.com/ovn-org/libovsdb/cache/cache.go:101 +0x139 github.com/ovn-org/libovsdb/cache.(*RowCache).RowByModel(0xc000bf2d80, 0x1a8e8e0, 0xc0046c0000, 0x0, 0x0) /go/src/github.com/openshift/ovn-kubernetes/go-controller/vendor/github.com/ovn-org/libovsdb/cache/cache.go:130 +0x417 github.com/ovn-org/libovsdb/client.api.Get(0xc000bf3680, 0x0, 0x0, 0xc000183f98, 0x21135a0, 0xc003394600, 0x1a8e8e0, 0xc0046c0000, 0xc00416e300, 0x0) /go/src/github.com/openshift/ovn-kubernetes/go-controller/vendor/github.com/ovn-org/libovsdb/client/api.go:221 +0xd0 github.com/ovn-org/libovsdb/client.(*ovsdbClient).Get(0xc0001c48f0, 0x21135a0, 0xc003394600, 0x1a8e8e0, 0xc0046c0000, 0x0, 0x0) /go/src/github.com/openshift/ovn-kubernetes/go-controller/vendor/github.com/ovn-org/libovsdb/client/client.go:1189 +0x139 github.com/ovn-org/ovn-kubernetes/go-controller/pkg/ovn.ovnNBLSPDel(0x2138198, 0xc00002d640, 0xc0038731b8, 0x17, 0xc002501b60, 0x29, 0x0, 0x0) /go/src/github.com/openshift/ovn-kubernetes/go-controller/pkg/ovn/pods.go:649 +0x265 github.com/ovn-org/ovn-kubernetes/go-controller/pkg/ovn.(*Controller).deleteLogicalPort(0xc00000e1e0, 0xc002f40400) /go/src/github.com/openshift/ovn-kubernetes/go-controller/pkg/ovn/pods.go:145 +0x46a goroutine 174 [semacquire, 12 minutes]: sync.runtime_SemacquireMutex(0xc000bf2e28, 0x4f1600, 0x0) /usr/lib/golang/src/runtime/sema.go:71 +0x47 sync.(*RWMutex).Lock(0xc000bf2e20) /usr/lib/golang/src/sync/rwmutex.go:116 +0x85 github.com/ovn-org/libovsdb/cache.(*RowCache).Update(0xc000bf2d80, 0xc002280570, 0x24, 0x1a8e8e0, 0xc0046c0600, 0xc003319200, 0x0, 0x0) /go/src/github.com/openshift/ovn-kubernetes/go-controller/vendor/github.com/ovn-org/libovsdb/cache/cache.go:176 +0x6f github.com/ovn-org/libovsdb/cache.(*TableCache).Populate2(0xc000bf3680, 0xc003766210, 0x0, 0x0) /go/src/github.com/openshift/ovn-kubernetes/go-controller/vendor/github.com/ovn-org/libovsdb/cache/cache.go:659 +0x7d6 github.com/ovn-org/libovsdb/cache.(*TableCache).Update2(0xc000bf3680, 0x1c71a40, 0xc003331980, 0xc003766210, 0x2e, 0x0) /go/src/github.com/openshift/ovn-kubernetes/go-controller/vendor/github.com/ovn-org/libovsdb/cache/cache.go:536 +0x6b github.com/ovn-org/libovsdb/client.(*ovsdbClient).update3(0xc0001c48f0, 0xc00451a660, 0x3, 0x4, 0xc003e32738, 0x7f225dc865b8, 0x41b69b) /go/src/github.com/openshift/ovn-kubernetes/go-controller/vendor/github.com/ovn-org/libovsdb/client/client.go:637 +0x55a github.com/ovn-org/libovsdb/client.(*ovsdbClient).createRPC2Client.func4(0xc000289500, 0xc00451a660, 0x3, 0x4, 0xc003e32738, 0x0, 0x0) /go/src/github.com/openshift/ovn-kubernetes/go-controller/vendor/github.com/ovn-org/libovsdb/client/client.go:395 +0x52 Signed-off-by: Dan Williams <dcbw@redhat.com>
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To pick up ovn-org/libovsdb#270 "cache: don't let RowByModel() recursively lock the RowCache" Signed-off-by: Dan Williams <dcbw@redhat.com>
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RWLocks are not supposed to be used recursively, and if something
else Locks the row cache then we deadlock.
In this example, goroutine 59 RLocks the RowCache, and then
goroutine 174 attempts to Lock the cache but blocks on #59's
RLock. Since there is a writer waiting to acquire the lock,
any further RLocks are effectively Locks, and thus when
goroutine #59 attempts to acquire the second RLock in Row()
it deadlocks against goroutine #174.