linux-toradex.git/include/linux/cgroup-defs.h, branch v4.9.16

cgroup, cpuset: replace cpuset_post_attach_flush() with cgroup_subsys->post_attach callback

2016-04-25T19:45:14+00:00

Since e93ad19d0564 ("cpuset: make mm migration asynchronous"), cpuset
kicks off asynchronous NUMA node migration if necessary during task
migration and flushes it from cpuset_post_attach_flush() which is
called at the end of __cgroup_procs_write().  This is to avoid
performing migration with cgroup_threadgroup_rwsem write-locked which
can lead to deadlock through dependency on kworker creation.

memcg has a similar issue with charge moving, so let's convert it to
an official callback rather than the current one-off cpuset specific
function.  This patch adds cgroup_subsys->post_attach callback and
makes cpuset register cpuset_post_attach_flush() as its ->post_attach.

The conversion is mostly one-to-one except that the new callback is
called under cgroup_mutex.  This is to guarantee that no other
migration operations are started before ->post_attach callbacks are
finished.  cgroup_mutex is one of the outermost mutex in the system
and has never been and shouldn't be a problem.  We can add specialized
synchronization around __cgroup_procs_write() but I don't think
there's any noticeable benefit.

Signed-off-by: Tejun Heo 
Cc: Li Zefan 
Cc: Johannes Weiner 
Cc: Michal Hocko 
Cc:  # 4.4+ prerequisite for the next patch

cgroup: ignore css_sets associated with dead cgroups during migration

2016-03-16T20:31:46+00:00

Before 2e91fa7f6d45 ("cgroup: keep zombies associated with their
original cgroups"), all dead tasks were associated with init_css_set.
If a zombie task is requested for migration, while migration prep
operations would still be performed on init_css_set, the actual
migration would ignore zombie tasks.  As init_css_set is always valid,
this worked fine.

However, after 2e91fa7f6d45, zombie tasks stay with the css_set it was
associated with at the time of death.  Let's say a task T associated
with cgroup A on hierarchy H-1 and cgroup B on hiearchy H-2.  After T
becomes a zombie, it would still remain associated with A and B.  If A
only contains zombie tasks, it can be removed.  On removal, A gets
marked offline but stays pinned until all zombies are drained.  At
this point, if migration is initiated on T to a cgroup C on hierarchy
H-2, migration path would try to prepare T's css_set for migration and
trigger the following.

 WARNING: CPU: 0 PID: 1576 at kernel/cgroup.c:474 cgroup_get+0x121/0x160()
 CPU: 0 PID: 1576 Comm: bash Not tainted 4.4.0-work+ #289
 ...
 Call Trace:
  [] dump_stack+0x4e/0x82
  [] warn_slowpath_common+0x78/0xb0
  [] warn_slowpath_null+0x15/0x20
  [] cgroup_get+0x121/0x160
  [] link_css_set+0x7b/0x90
  [] find_css_set+0x3bc/0x5e0
  [] cgroup_migrate_prepare_dst+0x89/0x1f0
  [] cgroup_attach_task+0x157/0x230
  [] __cgroup_procs_write+0x2b7/0x470
  [] cgroup_tasks_write+0xc/0x10
  [] cgroup_file_write+0x30/0x1b0
  [] kernfs_fop_write+0x13c/0x180
  [] __vfs_write+0x23/0xe0
  [] vfs_write+0xa4/0x1a0
  [] SyS_write+0x44/0xa0
  [] entry_SYSCALL_64_fastpath+0x12/0x6f

It doesn't make sense to prepare migration for css_sets pointing to
dead cgroups as they are guaranteed to contain only zombies which are
ignored later during migration.  This patch makes cgroup destruction
path mark all affected css_sets as dead and updates the migration path
to ignore them during preparation.

Signed-off-by: Tejun Heo 
Fixes: 2e91fa7f6d45 ("cgroup: keep zombies associated with their original cgroups")
Cc: stable@vger.kernel.org # v4.4+

cgroup: implement cgroup_subsys->implicit_on_dfl

2016-03-08T16:51:26+00:00

Some controllers, perf_event for now and possibly freezer in the
future, don't really make sense to control explicitly through
"cgroup.subtree_control".  For example, the primary role of perf_event
is identifying the cgroups of tasks; however, because the controller
also keeps a small amount of state per cgroup, it can't be replaced
with simple cgroup membership tests.

This patch implements cgroup_subsys->implicit_on_dfl flag.  When set,
the controller is implicitly enabled on all cgroups on the v2
hierarchy so that utility type controllers such as perf_event can be
enabled and function transparently.

An implicit controller doesn't show up in "cgroup.controllers" or
"cgroup.subtree_control", is exempt from no internal process rule and
can be stolen from the default hierarchy even if there are non-root
csses.

v2: Reimplemented on top of the recent updates to css handling and
    subsystem rebinding.  Rebinding implicit subsystems is now a
    simple matter of exempting it from the busy subsystem check.

Signed-off-by: Tejun Heo

cgroup: use css_set->mg_dst_cgrp for the migration target cgroup

2016-03-08T16:51:26+00:00

Migration can be multi-target on the default hierarchy when a
controller is enabled - processes belonging to each child cgroup have
to be moved to the child cgroup itself to refresh css association.

This isn't a problem for cgroup_migrate_add_src() as each source
css_set still maps to single source and target cgroups; however,
cgroup_migrate_prepare_dst() is called once after all source css_sets
are added and thus might not have a single destination cgroup.  This
is currently worked around by specifying NULL for @dst_cgrp and using
the source's default cgroup as destination as the only multi-target
migration in use is self-targetting.  While this works, it's subtle
and clunky.

As all taget cgroups are already specified while preparing the source
css_sets, this clunkiness can easily be removed by recording the
target cgroup in each source css_set.  This patch adds
css_set->mg_dst_cgrp which is recorded on cgroup_migrate_src() and
used by cgroup_migrate_prepare_dst().  This also makes migration code
ready for arbitrary multi-target migration.

Signed-off-by: Tejun Heo

cgroup: introduce cgroup_{save|propagate|restore}_control()

2016-03-03T14:57:59+00:00

While controllers are being enabled and disabled in
cgroup_subtree_control_write(), the original subsystem masks are
stashed in local variables so that they can be restored if the
operation fails in the middle.

This patch adds dedicated fields to struct cgroup to be used instead
of the local variables and implements functions to stash the current
values, propagate the changes and restore them recursively.  Combined
with the previous changes, this makes subsystem management operations
fully recursive and modularlized.  This will be used to expand cgroup
core functionalities.

While at it, remove now unused @css_enable and @css_disable from
cgroup_subtree_control_write().

Signed-off-by: Tejun Heo 
Acked-by: Zefan Li

cgroup: explicitly track whether a cgroup_subsys_state is visible to userland

2016-03-03T14:57:58+00:00

Currently, whether a css (cgroup_subsys_state) has its interface files
created is not tracked and assumed to change together with the owning
cgroup's lifecycle.  cgroup directory and interface creation is being
separated out from internal object creation to help refactoring and
eventually allow cgroups which are not visible through cgroupfs.

This patch adds CSS_VISIBLE to track whether a css has its interface
files created and perform management operations only when necessary
which helps decoupling interface file handling from internal object
lifecycle.  After this patch, all css interface file management
functions can be called regardless of the current state and will
achieve the expected result.

Signed-off-by: Tejun Heo 
Acked-by: Zefan Li

cgroup: convert cgroup_subsys flag fields to bool bitfields

2016-02-23T15:00:50+00:00

Signed-off-by: Tejun Heo 
Cc: Li Zefan 
Cc: Ingo Molnar 
Cc: Peter Zijlstra

cgroup: make cgroup subsystem masks u16

2016-02-23T03:25:47+00:00

After the recent do_each_subsys_mask() conversion, there's no reason
to use ulong for subsystem masks.  We'll be adding more subsystem
masks to persistent data structures, let's reduce its size to u16
which should be enough for now and the foreseeable future.

This doesn't create any noticeable behavior differences.

v2: Johannes spotted that the initial patch missed cgroup_no_v1_mask.
    Converted.

Signed-off-by: Tejun Heo 
Acked-by: Johannes Weiner

cgroup: s/child_subsys_mask/subtree_ss_mask/

2016-02-23T03:25:46+00:00

For consistency with cgroup->subtree_control.

* cgroup->child_subsys_mask -> cgroup->subtree_ss_mask
* cgroup_calc_child_subsys_mask() -> cgroup_calc_subtree_ss_mask()
* cgroup_refresh_child_subsys_mask() -> cgroup_refresh_subtree_ss_mask()

No functional changes.

Signed-off-by: Tejun Heo 
Acked-by: Johannes Weiner

Revert "cgroup: add cgroup_subsys->css_e_css_changed()"

2016-02-23T03:25:46+00:00

This reverts commit 56c807ba4e91f0980567b6a69de239677879b17f.

cgroup_subsys->css_e_css_changed() was supposed to be used by cgroup
writeback support; however, the change to per-inode cgroup association
made it unnecessary and the callback doesn't have any user.  Remove
it.

Signed-off-by: Tejun Heo 
Acked-by: Johannes Weiner