Messages in this thread Patch in this message | | | Date | Tue, 5 Feb 2013 11:40:50 +0800 | From | Li Zefan <> | Subject | Re: [PATCH 1/4] eventfd: introduce eventfd_signal_hangup() |
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On 2013/2/4 18:15, Kirill A. Shutemov wrote: > On Sat, Feb 02, 2013 at 05:58:58PM +0200, Kirill A. Shutemov wrote: >> On Sat, Feb 02, 2013 at 02:50:44PM +0800, Li Zefan wrote: >>> When an eventfd is closed, a wakeup with POLLHUP will be issued, >>> but cgroup wants to issue wakeup explicitly, so when a cgroup is >>> removed userspace can be notified. >>> >>> Signed-off-by: Li Zefan <lizefan@huawei.com> > > Hm.. Looks like it will break eventfd semantics: > > 1. One eventfd can be used for deliver more then one notification from > one or more cgroups. POLLHUP on removing one of cgroups is not valid. > > 2. It's valid to have eventfd opened only by one userspace application. We > should not close it, just because cgroup is removed. > > I think problem with multiple threads waiting an event on eventfd should > be handled in userspace. >
I didn't realize this.. and if a cgroup is removed, the woken thread may not be the thread that is waiting on this cgroup. How crappy.. I don't know how userspace is going to deal with all these.
And another bug spotted. We can pass fd of memory.usage_in_bytes of cgroup A to cgroup.event_control of cgroup B, and then we won't get memory usage notification from A but B! What's worse, if A and B are in different mount hierarchy, boom!
Signed-off-by: Li Zefan <lizefan@huawei.com> --- kernel/cgroup.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 3d21adf..e496359 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -3825,6 +3825,7 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft, const char *buffer) { struct cgroup_event *event = NULL; + struct cgroup *cgrp_cfile; unsigned int efd, cfd; struct file *efile = NULL; struct file *cfile = NULL; @@ -3880,6 +3881,16 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft, goto fail; } + /* + * The file to be monitored must be in the same cgroup as + * cgroup.event_control is. + */ + cgrp_cfile = __d_cgrp(cfile->f_dentry->d_parent); + if (cgrp_cfile != cgrp) { + ret = -EINVAL; + goto fail; + } + if (!event->cft->register_event || !event->cft->unregister_event) { ret = -EINVAL; goto fail; -- 1.8.0.2
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