Stop locking container exec store while starting

The daemon.containerd.Exec call does not access or mutate the
container's ExecCommands store in any way, and locking the exec config
is sufficient to synchronize with the event-processing loop. Locking
the ExecCommands store while starting the exec process only serves to
block unrelated operations on the container for an extended period of
time.

Convert the Store struct's mutex to an unexported field to prevent this
from regressing in the future.

Signed-off-by: Cory Snider <csnider@mirantis.com>

daemon/exec.go

@@ -276,18 +276,15 @@ func (daemon *Daemon) ContainerExecStart(ctx context.Context, name string, optio
 
 	// Synchronize with libcontainerd event loop
 	ec.Lock()
-	c.ExecCommands.Lock()
 	systemPid, err := daemon.containerd.Exec(ctx, c.ID, ec.ID, p, cStdin != nil, ec.InitializeStdio)
 	// the exec context should be ready, or error happened.
 	// close the chan to notify readiness
 	close(ec.Started)
 	if err != nil {
-		c.ExecCommands.Unlock()
 		ec.Unlock()
 		return translateContainerdStartErr(ec.Entrypoint, ec.SetExitCode, err)
 	}
 	ec.Pid = systemPid
-	c.ExecCommands.Unlock()
 	ec.Unlock()
 
 	select {

daemon/exec/exec.go

@@ -93,7 +93,7 @@ func (c *Config) SetExitCode(code int) {
 // Store keeps track of the exec configurations.
 type Store struct {
 	byID map[string]*Config
-	sync.RWMutex
+	mu   sync.RWMutex
 }
 
 // NewStore initializes a new exec store.
@@ -105,44 +105,44 @@ func NewStore() *Store {
 
 // Commands returns the exec configurations in the store.
 func (e *Store) Commands() map[string]*Config {
-	e.RLock()
+	e.mu.RLock()
 	byID := make(map[string]*Config, len(e.byID))
 	for id, config := range e.byID {
 		byID[id] = config
 	}
-	e.RUnlock()
+	e.mu.RUnlock()
 	return byID
 }
 
 // Add adds a new exec configuration to the store.
 func (e *Store) Add(id string, Config *Config) {
-	e.Lock()
+	e.mu.Lock()
 	e.byID[id] = Config
-	e.Unlock()
+	e.mu.Unlock()
 }
 
 // Get returns an exec configuration by its id.
 func (e *Store) Get(id string) *Config {
-	e.RLock()
+	e.mu.RLock()
 	res := e.byID[id]
-	e.RUnlock()
+	e.mu.RUnlock()
 	return res
 }
 
 // Delete removes an exec configuration from the store.
 func (e *Store) Delete(id string, pid int) {
-	e.Lock()
+	e.mu.Lock()
 	delete(e.byID, id)
-	e.Unlock()
+	e.mu.Unlock()
 }
 
 // List returns the list of exec ids in the store.
 func (e *Store) List() []string {
 	var IDs []string
-	e.RLock()
+	e.mu.RLock()
 	for id := range e.byID {
 		IDs = append(IDs, id)
 	}
-	e.RUnlock()
+	e.mu.RUnlock()
 	return IDs
 }