Messages in this thread Patch in this message | | | Date | Wed, 21 Jan 2009 02:00:56 -0800 | Subject | Re: [RFC][PATCH 4/4] cgroup-memcg fix frequent EBUSY at rmdir v2 | From | Paul Menage <> |
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On Tue, Jan 20, 2009 at 2:47 AM, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > CGRP_NOTIFY_ON_RELEASE, > + /* Someone calls rmdir() and is wating for this cgroup is released */
/* A thread is in rmdir() waiting to destroy this cgroup */
Also document that it can only be set/cleared when you're holding the inode_sem for the cgroup directory. And we should probably move this enum inside cgroup.c, since nothing in the header file uses it.
> + CGRP_WAIT_ON_RMDIR, > };
> > struct cgroup { > @@ -350,7 +352,7 @@ int cgroup_is_descendant(const struct cg > struct cgroup_subsys { > struct cgroup_subsys_state *(*create)(struct cgroup_subsys *ss, > struct cgroup *cgrp); > - void (*pre_destroy)(struct cgroup_subsys *ss, struct cgroup *cgrp); > + int (*pre_destroy)(struct cgroup_subsys *ss, struct cgroup *cgrp);
Can you update the documentation to indicate what an error result from pre_destroy indicates? Can pre_destroy() be called multiple times for the same subsystem/cgroup?
> + > + /* wake up rmdir() waiter....it should fail.*/
/* Wake up rmdir() waiter - the rmdir should fail since the cgroup is no longer empty */
But is this safe? If we do a pre-destroy, is it OK to let new tasks into the cgroup?
> @@ -2446,6 +2461,8 @@ static long cgroup_create(struct cgroup > > mutex_unlock(&cgroup_mutex); > mutex_unlock(&cgrp->dentry->d_inode->i_mutex); > + if (wakeup_on_rmdir(parent)) > + cgroup_rmdir_wakeup_waiters();
I don't think that there can be a waiter, since rmdir() would hold the parent's inode semaphore, which would block this thread before it gets to cgroup_create()
> +DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq); > + > +static void cgroup_rmdir_wakeup_waiters(void) > +{ > + wake_up_all(&cgroup_rmdir_waitq); > +} > +
I think you can merge wakeup_on_rmdir() and cgroup_rmdir_wakeup_waiters() into a single function, cgroup_wakeup_rmdir(struct cgroup *)
> > + if (signal_pending(current)) > + return -EINTR;
I think it would be better to move this check to after we've already failed on cgroup_clear_css_refs(). That way we can't fail with an EINTR just because we raced with a signal on the way into rmdir() - we have to actually hit the EBUSY and try to sleep. > + ret = cgroup_call_pre_destroy(cgrp); > + if (ret == -EBUSY) > + return -EBUSY; What about other potential error codes? If the subsystem's only allowed to return 0 or EBUSY, then we should check for that.
Paul
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