e0456faac2
As pointed out by Tonis, there's a race between ReleaseRWLayer() and GetRWLayer(): ``` ----- goroutine 1 ----- ----- goroutine 2 ----- ReleaseRWLayer() m := ls.mounts[l.Name()] ... m.deleteReference(l) m.hasReferences() ... GetRWLayer() ... mount := ls.mounts[id] ls.driver.Remove(m.mountID) ls.store.RemoveMount(m.name) return mount.getReference() delete(ls.mounts, m.Name()) ----------------------- ----------------------- ``` When something like this happens, GetRWLayer will return an RWLayer without a storage. Oops. There might be more races like this, and it seems the best solution is to lock by layer id/name by using pkg/locker. With this in place, name collision could not happen, so remove the part of previous commit that protected against it in CreateRWLayer (temporary nil assigmment and associated rollback). So, now we have * layerStore.mountL sync.Mutex to protect layerStore.mount map[] (against concurrent access); * mountedLayer's embedded `sync.Mutex` to protect its references map[]; * layerStore.layerL (which I haven't touched); * per-id locker, to avoid name conflicts and concurrent operations on the same rw layer. The whole rig seems to look more readable now (mutexes use is straightforward, no nested locks). Reported-by: Tonis Tiigi <tonistiigi@gmail.com> Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com> Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com> (cherry picked from commit af433dd200f8287305b1531d5058780be36b7e2e) Signed-off-by: Sebastiaan van Stijn <github@gone.nl> Upstream-commit: 1ebe324c6a481de86a5b84494057a639773624f1 Component: engine