fix(libkb): take the write lock in the remaining cache setters

SetImplicitTeamConflictInfoCacher, SetImplicitTeamCacher and
SetKVRevisionCache mutated GlobalContext fields while holding only
cacheMu.RLock(), which races with concurrent getters.

Also document why the annotated team cache ages entries from the load
start rather than the load finish.

Author: chrisnojima

go/libkb/globals.go

@@ -754,8 +754,8 @@ func (g *GlobalContext) GetImplicitTeamConflictInfoCacher() LRUer {
 }
 
 func (g *GlobalContext) SetImplicitTeamConflictInfoCacher(l LRUer) {
-	g.cacheMu.RLock()
-	defer g.cacheMu.RUnlock()
+	g.cacheMu.Lock()
+	defer g.cacheMu.Unlock()
 	g.itciCacher = l
 }
 
@@ -766,8 +766,8 @@ func (g *GlobalContext) GetImplicitTeamCacher() MemLRUer {
 }
 
 func (g *GlobalContext) SetImplicitTeamCacher(l MemLRUer) {
-	g.cacheMu.RLock()
-	defer g.cacheMu.RUnlock()
+	g.cacheMu.Lock()
+	defer g.cacheMu.Unlock()
 	g.iteamCacher = l
 }
 
@@ -778,9 +778,6 @@ func (g *GlobalContext) GetAnnotatedTeamCacher() AnnotatedTeamCacher {
 }
 
 func (g *GlobalContext) SetAnnotatedTeamCacher(c AnnotatedTeamCacher) {
-	// a write needs the write lock: GetAnnotatedTeamCacher runs from
-	// NotifyRouter.HandleTeamChangedByID on every team notification. The
-	// neighbouring setters take RLock here too, and are equally wrong.
 	g.cacheMu.Lock()
 	defer g.cacheMu.Unlock()
 	g.annotatedTeamCacher = c
@@ -793,8 +790,8 @@ func (g *GlobalContext) GetKVRevisionCache() KVRevisionCacher {
 }
 
 func (g *GlobalContext) SetKVRevisionCache(kvr KVRevisionCacher) {
-	g.cacheMu.RLock()
-	defer g.cacheMu.RUnlock()
+	g.cacheMu.Lock()
+	defer g.cacheMu.Unlock()
 	g.kvRevisionCache = kvr
 }
 

go/teams/annotated_cache.go

@@ -151,6 +151,9 @@ func (c *annotatedTeamCache) load(mctx libkb.MetaContext, teamID keybase1.TeamID
 			}()
 		}
 
+		// Age the entry from when the load started, not when it finished: the
+		// data describes the server state as of the request, so a slow loader
+		// must not buy the result extra TTL it has already spent being stale.
 		startedAt := mctx.G().Clock().Now()
 		res, err = loader(mctx.Ctx(), mctx.G(), teamID)