于 2012/10/17 16:28, Li Zefan 写道: > On 2012/10/17 6:28, Tejun Heo wrote: >> cgroup core has a bug which violates a basic rule about event >> notifications - when a new entity needs to be added, you add that to >> the notification list first and then make the new entity conform to >> the current state. If done in the reverse order, an event happening >> inbetween will be lost. >> >> cgroup_subsys->fork() is invoked way before the new task is added to >> the css_set. Currently, cgroup_freezer is the only user of ->fork() >> and uses it to make new tasks conform to the current state of the >> freezer. If FROZEN state is requested while fork is in progress >> between cgroup_fork_callbacks() and cgroup_post_fork(), the child >> could escape freezing - the cgroup isn't frozen when ->fork() is >> called and the freezer couldn't see the new task on the css_set. >> >> This patch moves cgroup_subsys->fork() invocation to >> cgroup_post_fork() after the new task is added to the css_set. >> cgroup_fork_callbacks() is removed. >> >> Because now a task may be migrated during cgroup_subsys->fork(), >> freezer_fork() is updated so that it adheres to the usual RCU locking >> and the rather pointless comment on why locking can be different there >> is removed (if it doesn't make anything simpler, why even bother?). >> > > I don't think rcu read section is sufficient. It guarantees the data you're > accessing is valid, but the data can be new or can be old. > > So a case below is possible: > > in freezer_fork(): > rcu_read_lock(); > freezer = task_freezer(task); > move task from freezer to freezer2 > which is in FREEZING/FROZEN state > freezer is in THAWED state, > nothing to do. > rcu_read_unlock(); > forget about it. The task will be correctly frozen when moving to another cgroup, so nothing unexpected will happen. for this patch: Acked-by: Li Zefan <lizefan@xxxxxxxxxx> _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
