cgroups: fix race between userspace and kernelspace
authorKirill A. Shutemov <kirill@shutemov.name>
Wed, 10 Mar 2010 23:22:34 +0000 (15:22 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Fri, 12 Mar 2010 23:52:37 +0000 (15:52 -0800)
commit4ab78683c17d739c2a2077141dcf81a02b7fb57e
tree5884c1b7e20d1975d668d07dbf43202d737ec7bf
parentdaaf1e68874c078a15ae6ae827751839c4d81739
cgroups: fix race between userspace and kernelspace

Notify userspace about cgroup removing only after rmdir of cgroup
directory to avoid race between userspace and kernelspace.

eventfd are used to notify about two types of event:
 - control file-specific, like crossing memory threshold;
 - cgroup removing.

To understand what really happen, userspace can check if the cgroup still
exists.  To avoid race beetween userspace and kernelspace we have to
notify userspace about cgroup removing only after rmdir of cgroup
directory.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Dan Malek <dan@embeddedalley.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/cgroup.c