Re: [PATCH] cgroup: fix dentry still in use bug when dropping css refs after umount
Hello, On Tue, Jul 10, 2012 at 10:11:05AM +0800, Li Zefan wrote: > Right, but that should be safe. The css objects of the root cgroup are > allocated at boot, and won't be destroyed at umount. > > Furthermore when a cgroup hierarchy is going to be unmounted, those css's > will be made to point to a cgroup named dummytop in rebind_subsystems(), > and there's a syncronize_rcu() in the end of the function, so accessing > css->cgroup is always safe. > > In this case, dummytop->dentry is NULL, and that's safe too, because > cgroup_path() is aware of this case. I see. Thanks for the explanation. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] cgroup: fix dentry still in use bug when dropping css refs after umount
On 2012/7/8 14:35, Tejun Heo wrote: > Hello, Li. > > On Wed, Jul 04, 2012 at 02:19:15PM +0800, Li Zefan wrote: >>> I think we're horridly broken for >>> root cgroup tho - and it has been broken for very long time. I think >>> it's mostly hidden because most (all?) controllers short-circuit root >>> cgroup. Eh, well >>> >> >> Could you elaborate a bit on what's broken for root cgroup? > > If someone holds css ref of a root cgroup, AFAICS nothing is > preventing the cgroup hierarchy from being unmounted and root cgroup > destroyed. > Right, but that should be safe. The css objects of the root cgroup are allocated at boot, and won't be destroyed at umount. Furthermore when a cgroup hierarchy is going to be unmounted, those css's will be made to point to a cgroup named dummytop in rebind_subsystems(), and there's a syncronize_rcu() in the end of the function, so accessing css->cgroup is always safe. In this case, dummytop->dentry is NULL, and that's safe too, because cgroup_path() is aware of this case. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] cgroup: fix dentry still in use bug when dropping css refs after umount
Hello, Li. On Wed, Jul 04, 2012 at 02:19:15PM +0800, Li Zefan wrote: > > I think we're horridly broken for > > root cgroup tho - and it has been broken for very long time. I think > > it's mostly hidden because most (all?) controllers short-circuit root > > cgroup. Eh, well > > > > Could you elaborate a bit on what's broken for root cgroup? If someone holds css ref of a root cgroup, AFAICS nothing is preventing the cgroup hierarchy from being unmounted and root cgroup destroyed. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
