Up until now, cgroup_freezer didn't implement hierarchy properly.
cgroups could be arranged in hierarchy but it didn't make any
difference in how each cgroup_freezer behaved. They all operated
separately.
This patch implements proper hierarchy support. If a cgroup is
frozen, all its descendants are frozen. A cgroup is thawed iff it and
all its ancestors are THAWED. freezer.self_freezing shows the current
freezing state for the cgroup itself. freezer.parent_freezing shows
whether the cgroup is freezing because any of its ancestors is
freezing.
freezer_post_create() locks the parent and new cgroup and inherits the
parent's state and freezer_change_state() applies new state top-down
using cgroup_for_each_descendant_pre() which guarantees that no child
can escape its parent's state. update_if_frozen() uses
cgroup_for_each_descendant_post() to propagate frozen states
bottom-up.
Synchronization could be coarser and easier by using a single mutex to
protect all hierarchy operations. Finer grained approach was used
because it wasn't too difficult for cgroup_freezer and I think it's
beneficial to have an example implementation and cgroup_freezer is
rather simple and can serve a good one.
As this makes cgroup_freezer properly hierarchical,
freezer_subsys.broken_hierarchy marking is removed.
Note that this patch changes userland visible behavior - freezing a
cgroup now freezes all its descendants too. This behavior change is
intended and has been warned via .broken_hierarchy.
v2: Michal spotted a bug in freezer_change_state() - descendants were
inheriting from the wrong ancestor. Fixed.
v3: Documentation/cgroups/freezer-subsystem.txt updated.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Fix a typo in Documentation/cgroups/freezer-subsystem.txt.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
According to commit 676db4af04 ("cgroupfs: create /sys/fs/cgroup to
mount cgroupfs on") the canonical mountpoint for the cgroup filesystem
is /sys/fs/cgroup. Hence, this should be used in the documentation.
Signed-off-by: Jörg Sommer <joerg@alea.gnuu.de>
Acked-by: Paul Menage <menage@google.com>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
With this change, control file 'freezer.state' doesn't exist in root
cgroup, making root cgroup unfreezable.
I think it's reasonable to disallow freeze tasks in the root cgroup. And
then we can avoid fork overhead when freezer subsystem is compiled but not
used.
Also make writing invalid value to freezer.state returns EINVAL rather
than EIO. This is more consistent with other cgroup subsystem.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Paul Menage <menage@google.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: "Serge E. Hallyn" <serue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Describe why we need the freezer subsystem and how to use it in a
documentation file. Since the cgroups.txt file is focused on the
subsystem-agnostic portions of cgroups make a directory and move the old
cgroups.txt file at the same time.
Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: containers@lists.linux-foundation.org
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
