cgroup_scan_tasks() takes a pointer to struct cgroup_scanner as its
sole argument and the only function of that struct is packing the
arguments of the function call which are consisted of five fields.
It's not too unusual to pack parameters into a struct when the number
of arguments gets excessive or the whole set needs to be passed around
a lot, but neither holds here making it just weird.

Drop struct cgroup_scanner and pass the params directly to
cgroup_scan_tasks().  Note that struct cpuset_change_nodemask_arg was
added to cpuset.c to pass both ->cs and ->newmems pointer to
cpuset_change_nodemask() using single data pointer.

This doesn't make any functional differences.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

Currently all cgroup_task_iter functions require @cgrp to be passed
in, which is superflous and increases chance of usage error.  Make
cgroup_task_iter remember the cgroup being iterated and drop @cgrp
argument from next and end functions.

This patch doesn't introduce any behavior differences.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>

cgroup now has multiple iterators and it's quite confusing to have
something which walks over tasks of a single cgroup named cgroup_iter.
Let's rename it to cgroup_task_iter.

While at it, reformat / update comments and replace the overview
comment above the interface function decls with proper function
comments.  Such overview can be useful but function comments should be
more than enough here.

This is pure rename and doesn't introduce any functional changes.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>

For some reason, cgroup_advance_iter() is standing lonely all away
from its iter comrades.  Relocate it.

This is cosmetic.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

cgroup is currently in the process of transitioning to using css
(cgroup_subsys_state) as the primary handle instead of cgroup in
subsystem API.  For hierarchy iterators, this is beneficial because

* In most cases, css is the only thing subsystems care about anyway.

* On the planned unified hierarchy, iterations for different
  subsystems will need to skip over different subtrees of the
  hierarchy depending on which subsystems are enabled on each cgroup.
  Passing around css makes it unnecessary to explicitly specify the
  subsystem in question as css is intersection between cgroup and
  subsystem

* For the planned unified hierarchy, css's would need to be created
  and destroyed dynamically independent from cgroup hierarchy.  Having
  cgroup core manage css iteration makes enforcing deref rules a lot
  easier.

Most subsystem conversions are straight-forward.  Noteworthy changes
are

* blkio: cgroup_to_blkcg() is no longer used.  Removed.

* freezer: cgroup_freezer() is no longer used.  Removed.

* devices: cgroup_to_devcgroup() is no longer used.  Removed.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Acked-by: NVivek Goyal <vgoyal@redhat.com>
Acked-by: NAristeu Rozanski <aris@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: Jens Axboe <axboe@kernel.dk>

There are several places where the children list is accessed directly.
This patch converts those places to use cgroup_next_child().  This
will help updating the hierarchy iterators to use @css instead of
@cgrp.

While cgroup_next_child() can be heavy in pathological cases - e.g. a
lot of dead children, this shouldn't cause any noticeable behavior
differences.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

cgroup is transitioning to using css (cgroup_subsys_state) as the main
subsys interface handle instead of cgroup and the iterators will be
updated to use css too.  The iterators need to walk the cgroup
hierarchy and return the css's matching the origin css, which is a bit
cumbersome to open code.

This patch converts cgroup_next_sibling() to cgroup_next_child() so
that it can handle all steps of direct child iteration.  This will be
used to update iterators to take @css instead of @cgrp.  In addition
to the new iteration init handling, cgroup_next_child() is
restructured so that the different branches share the end of iteration
condition check.

This patch doesn't change any behavior.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

cgroup is currently in the process of transitioning to using struct
cgroup_subsys_state * as the primary handle instead of struct cgroup.
Please see the previous commit which converts the subsystem methods
for rationale.

This patch converts all cftype file operations to take @css instead of
@cgroup.  cftypes for the cgroup core files don't have their subsytem
pointer set.  These will automatically use the dummy_css added by the
previous patch and can be converted the same way.

Most subsystem conversions are straight forwards but there are some
interesting ones.

* freezer: update_if_frozen() is also converted to take @css instead
  of @cgroup for consistency.  This will make the code look simpler
  too once iterators are converted to use css.

* memory/vmpressure: mem_cgroup_from_css() needs to be exported to
  vmpressure while mem_cgroup_from_cont() can be made static.
  Updated accordingly.

* cpu: cgroup_tg() doesn't have any user left.  Removed.

* cpuacct: cgroup_ca() doesn't have any user left.  Removed.

* hugetlb: hugetlb_cgroup_form_cgroup() doesn't have any user left.
  Removed.

* net_cls: cgrp_cls_state() doesn't have any user left.  Removed.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Acked-by: NVivek Goyal <vgoyal@redhat.com>
Acked-by: NAristeu Rozanski <aris@redhat.com>
Acked-by: NDaniel Wagner <daniel.wagner@bmw-carit.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Steven Rostedt <rostedt@goodmis.org>

cgroup subsystem API is being converted to use css
(cgroup_subsys_state) as the main handle, which makes things a bit
awkward for subsystem agnostic core features - the "cgroup.*"
interface files and various iterations - a bit awkward as they don't
have a css to use.

This patch adds cgroup->dummy_css which has NULL ->ss and whose only
role is pointing back to the cgroup.  This will be used to support
subsystem agnostic features on the coming css based API.

css_parent() is updated to handle dummy_css's.  Note that css will
soon grow its own ->parent field and css_parent() will be made
trivial.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

Previously, each file read/write operation relied on the inode
reference count pinning the cgroup and simply checked whether the
cgroup was marked dead before proceeding to invoke the per-subsystem
callback.  This was rather silly as it didn't have any synchronization
or css pinning around the check and the cgroup may be removed and all
css refs drained between the DEAD check and actual method invocation.

This patch pins the css between open() and release() so that it is
guaranteed to be alive for all file operations and remove the silly
DEAD checks from cgroup_file_read/write().
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

cgroup is transitioning to using css (cgroup_subsys_state) instead of
cgroup as the primary subsystem handle.  The cgroupfs file interface
will be converted to use css's which requires finding out the
subsystem from cftype so that the matching css can be determined from
the cgroup.

This patch adds cftype->ss which points to the subsystem the file
belongs to.  The field is initialized while a cftype is being
registered.  This makes it unnecessary to explicitly specify the
subsystem for other cftype handling functions.  @ss argument dropped
from various cftype handling functions.

This patch shouldn't introduce any behavior differences.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NVivek Goyal <vgoyal@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>

cgroup is currently in the process of transitioning to using struct
cgroup_subsys_state * as the primary handle instead of struct cgroup *
in subsystem implementations for the following reasons.

* With unified hierarchy, subsystems will be dynamically bound and
  unbound from cgroups and thus css's (cgroup_subsys_state) may be
  created and destroyed dynamically over the lifetime of a cgroup,
  which is different from the current state where all css's are
  allocated and destroyed together with the associated cgroup.  This
  in turn means that cgroup_css() should be synchronized and may
  return NULL, making it more cumbersome to use.

* Differing levels of per-subsystem granularity in the unified
  hierarchy means that the task and descendant iterators should behave
  differently depending on the specific subsystem the iteration is
  being performed for.

* In majority of the cases, subsystems only care about its part in the
  cgroup hierarchy - ie. the hierarchy of css's.  Subsystem methods
  often obtain the matching css pointer from the cgroup and don't
  bother with the cgroup pointer itself.  Passing around css fits
  much better.

This patch converts all cgroup_subsys methods to take @css instead of
@cgroup.  The conversions are mostly straight-forward.  A few
noteworthy changes are

* ->css_alloc() now takes css of the parent cgroup rather than the
  pointer to the new cgroup as the css for the new cgroup doesn't
  exist yet.  Knowing the parent css is enough for all the existing
  subsystems.

* In kernel/cgroup.c::offline_css(), unnecessary open coded css
  dereference is replaced with local variable access.

This patch shouldn't cause any behavior differences.

v2: Unnecessary explicit cgrp->subsys[] deref in css_online() replaced
    with local variable @css as suggested by Li Zefan.

    Rebased on top of new for-3.12 which includes for-3.11-fixes so
    that ->css_free() invocation added by da0a12ca ("cgroup: fix a
    leak when percpu_ref_init() fails") is converted too.  Suggested
    by Li Zefan.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Acked-by: NVivek Goyal <vgoyal@redhat.com>
Acked-by: NAristeu Rozanski <aris@redhat.com>
Acked-by: NDaniel Wagner <daniel.wagner@bmw-carit.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Steven Rostedt <rostedt@goodmis.org>

Currently, given a cgroup_subsys_state, there's no way to find out
which subsystem the css is for, which we'll need to convert the cgroup
controller API to primarily use @css instead of @cgroup.  This patch
adds cgroup_subsys_state->ss which points to the subsystem the @css
belongs to.

While at it, remove the comment about accessing @css->cgroup to
determine the hierarchy.  cgroup core will provide API to traverse
hierarchy of css'es and we don't want subsystems to directly walk
cgroup hierarchies anymore.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

The names of the two struct cgroup_subsys_state accessors -
cgroup_subsys_state() and task_subsys_state() - are somewhat awkward.
The former clashes with the type name and the latter doesn't even
indicate it's somehow related to cgroup.

We're about to revamp large portion of cgroup API, so, let's rename
them so that they're less awkward.  Most per-controller usages of the
accessors are localized in accessor wrappers and given the amount of
scheduled changes, this isn't gonna add any noticeable headache.

Rename cgroup_subsys_state() to cgroup_css() and task_subsys_state()
to task_css().  This patch is pure rename.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

It's a rw_semaphore not a mutex.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

It uses a single label and checks the validity of each pointer. This
is err-prone, and actually we had a bug because one of the check was
insufficient.

Use multi lables as we do in other places.

v2:
- drop initializations of local variables.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

This enables us to lookup a cgroup by its id.

v4:
- add a comment for idr_remove() in cgroup_offline_fn().

v3:
- on success, idr_alloc() returns the id but not 0, so fix the BUG_ON()
  in cgroup_init().
- pass the right value to idr_alloc() so that the id for dummy cgroup is 0.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Reviewed-by: NMichal Hocko <mhocko@suse.cz>
Signed-off-by: NTejun Heo <tj@kernel.org>

Constantly use @cset for css_set variables and use @cgrp as cgroup
variables.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

We can use struct cfent instead.

v2:
- remove cgroup_seqfile_release().
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

This should have been removed in commit d7eeac19
("cgroup: hold cgroup_mutex before calling css_offline").

While at it, update the comments.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

ss->css_free() is not called when perfcpu_ref_init() fails.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

rebind_subsystems() performs santiy checks even on subsystems which
aren't specified to be added or removed and the checks aren't all that
useful given that these are in a very cold path while the violations
they check would trip up in much hotter paths.

Let's remove these from rebind_subsystems().
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

Module ref handling in cgroup is rather weird.
parse_cgroupfs_options() grabs all the modules for the specified
subsystems.  A module ref is kept if the specified subsystem is newly
bound to the hierarchy.  If not, or the operation fails, the refs are
dropped.  This scatters module ref handling across multiple functions
making it difficult to track.  It also make the function nasty to use
for dynamic subsystem binding which is necessary for the planned
unified hierarchy.

There's nothing which requires the subsystem modules to be pinned
between parse_cgroupfs_options() and rebind_subsystems() in both mount
and remount paths.  parse_cgroupfs_options() can just parse and
rebind_subsystems() can handle pinning the subsystems that it wants to
bind, which is a natural part of its task - binding - anyway.

Move module ref handling into rebind_subsystems() which makes the code
a lot simpler - modules are gotten iff it's gonna be bound and put iff
unbound or binding fails.

v2: Li pointed out that if a controller module is unloaded between
    parsing and binding, rebind_subsystems() won't notice the missing
    controller as it only iterates through existing controllers.  Fix
    it by updating rebind_subsystems() to compare @added_mask to
    @pinned and fail with -ENOENT if they don't match.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

task_cgroup_path_from_hierarchy() was added for the planned new users
and none of the currently planned users wants to know about multiple
hierarchies.  This patch drops the multiple hierarchy part and makes
it always return the path in the first non-dummy hierarchy.

As unified hierarchy will always have id 1, this is guaranteed to
return the path for the unified hierarchy if mounted; otherwise, it
will return the path from the hierarchy which happens to occupy the
lowest hierarchy id, which will usually be the first hierarchy mounted
after boot.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>
Cc: Lennart Poettering <lennart@poettering.net>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Jan Kaluža <jkaluza@redhat.com>

rebind_subsystems() currently fails if the hierarchy has any !root
cgroups; however, on the planned unified hierarchy,
rebind_subsystems() will be used while populated.  Move the test to
cgroup_remount(), which is the only place the test is necessary
anyway.

As it's impossible for the other two callers of rebind_subsystems() to
have populated hierarchy, this doesn't make any behavior changes.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

Currently, creating and removing cgroup files in the root directory
are handled separately from the actual subsystem binding and unbinding
which happens in rebind_subsystems().  Also, rebind_subsystems() users
aren't handling file creation errors properly.  Let's integrate
top_cgroup file handling into rebind_subsystems() so that it's simpler
to use and everyone handles file creation errors correctly.

* On a successful return, rebind_subsystems() is guaranteed to have
  created all files of the new subsystems and deleted the ones
  belonging to the removed subsystems.  After a failure, no file is
  created or removed.

* cgroup_remount() no longer needs to make explicit populate/clear
  calls as it's all handled by rebind_subsystems(), and it gets proper
  error handling automatically.

* cgroup_mount() has been updated such that the root dentry and cgroup
  are linked before rebind_subsystems().  Also, the init_cred dancing
  and base file handling are moved right above rebind_subsystems()
  call and proper error handling for the base files is added.  While
  at it, add a comment explaining what's going on with the cred thing.

* cgroup_kill_sb() calls rebind_subsystems() to unbind all subsystems
  which now implies removing all subsystem files which requires the
  directory's i_mutex.  Grab it.  This means that files on the root
  cgroup are removed earlier - they used to be deleted from generic
  super_block cleanup from vfs.  This doesn't lead to any functional
  difference and it's cleaner to do the clean up explicitly for all
  files.

Combined with the previous changes, this makes all cgroup file
creation errors handled correctly.

v2: Added comment on init_cred.

v3: Li spotted that cgroup_mount() wasn't freeing tmp_links after base
    file addition failure.  Fix it by adding free_tmp_links error
    handling label.

v4: v3 introduced build bugs which got noticed by Fengguang's awesome
    kbuild test robot.  Fixed, and shame on me.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>

rebind_subsystems() will be updated to handle file creations and
removals with proper error handling and to do that will need to
perform file operations before actually adding the subsystem to the
hierarchy.

To enable such usage, update cgroup_populate/clear_dir() to use
for_each_subsys() instead of for_each_root_subsys() so that they
operate on all subsystems specified by @subsys_mask whether that
subsystem is currently bound to the hierarchy or not.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

cgroup_populate_dir() didn't use to check whether the actual file
creations were successful and could return success with only subset of
the requested files created, which is nasty.

This patch udpates cgroup_populate_dir() so that it either succeeds
with all files or fails with no file.

v2: The original patch also converted for_each_root_subsys() usages to
    for_each_subsys() without explaining why.  That part has been
    moved to a separate patch.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

cgroup_populate/clear_dir() currently take @base_files and adds and
removes, respectively, cgroup_base_files[] to the directory.  File
additions and removals are being reorganized for proper error handling
and more dynamic handling for the unified hierarchy, and mixing base
and subsys file handling into the same functions gets a bit confusing.

This patch moves base file handling out of cgroup_populate/clear_dir()
into their users - cgroup_mount(), cgroup_create() and
cgroup_destroy_locked().

Note that this changes the behavior of base file removal.  If
@base_files is %true, cgroup_clear_dir() used to delete files
regardless of cftype until there's no files left.  Now, only files
with matching cfts are removed.  As files can only be created by the
base or registered cftypes, this shouldn't result in any behavior
difference.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

cgroup_add_cftypes() uses cgroup_cfts_commit() to actually create the
files; however, both functions ignore actual file creation errors and
just assume success.  This can lead to, for example, blkio hierarchy
with some of the cgroups with only subset of interface files populated
after cfq-iosched is loaded under heavy memory pressure, which is
nasty.

This patch updates cgroup_cfts_commit() and cgroup_add_cftypes() to
guarantee that all files are created on success and no file is created
on failure.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

cgroup_addrm_files() mishandled error return value from
cgroup_add_file() and returns error iff the last file fails to create.
As we're in the process of cleaning up file add/rm error handling and
will reliably propagate file creation failures, there's no point in
keeping adding files after a failure.

Replace the broken error collection logic with immediate error return.
While at it, add lockdep assertions and function comment.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

* Rename it to cgroup_clear_dir() and make it take the pointer to the
  target cgroup instead of the the dentry.  This makes the function
  consistent with its counterpart - cgroup_populate_dir().

* Move cgroup_clear_directory() invocation from cgroup_d_remove_dir()
  to cgroup_remount() so that the function doesn't have to determine
  the cgroup pointer back from the dentry.  cgroup_d_remove_dir() now
  only deals with vfs, which is slightly cleaner.

This patch doesn't introduce any functional differences.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

0ce6cba3 ("cgroup: CGRP_ROOT_SUBSYS_BOUND should be ignored when
comparing mount options") only updated the remount path but
CGRP_ROOT_SUBSYS_BOUND should also be ignored when comparing options
while mounting an existing hierarchy.  As option mismatch triggers a
warning but doesn't fail the mount without sane_behavior, this only
triggers a spurious warning message.

Fix it by only comparing CGRP_ROOT_OPTION_MASK bits when comparing new
and existing root options.
Signed-off-by: NTejun Heo <tj@kernel.org>

1672d040 ("cgroup: fix cgroupfs_root early destruction path")
introduced CGRP_ROOT_SUBSYS_BOUND which is used to mark completion of
subsys binding on a new root; however, this broke remounts.
cgroup_remount() doesn't allow changing root options via remount and
CGRP_ROOT_SUBSYS_BOUND, which is set on all fully initialized roots,
makes the function reject all remounts.

Fix it by putting the options part in the lower 16 bits of root->flags
and masking the comparions.  While at it, make cgroup_remount() emit
an error message explaining why it's rejecting a remount request, so
that it's less of a mystery.
Signed-off-by: NTejun Heo <tj@kernel.org>

eb178d06 ("cgroup: grab cgroup_mutex in
drop_parsed_module_refcounts()") made drop_parsed_module_refcounts()
grab cgroup_mutex to make lockdep assertion in for_each_subsys()
happy.  Unfortunately, cgroup_remount() calls the function while
holding cgroup_mutex in its failure path leading to the following
deadlock.

# mount -t cgroup -o remount,memory,blkio cgroup blkio

 cgroup: option changes via remount are deprecated (pid=525 comm=mount)

 =============================================
 [ INFO: possible recursive locking detected ]
 3.10.0-rc4-work+ #1 Not tainted
 ---------------------------------------------
 mount/525 is trying to acquire lock:
  (cgroup_mutex){+.+.+.}, at: [<ffffffff8110a3e1>] drop_parsed_module_refcounts+0x21/0xb0

 but task is already holding lock:
  (cgroup_mutex){+.+.+.}, at: [<ffffffff8110e4e1>] cgroup_remount+0x51/0x200

 other info that might help us debug this:
  Possible unsafe locking scenario:

	CPU0
	----
   lock(cgroup_mutex);
   lock(cgroup_mutex);

  *** DEADLOCK ***

  May be due to missing lock nesting notation

 4 locks held by mount/525:
  #0:  (&type->s_umount_key#30){+.+...}, at: [<ffffffff811e9a0d>] do_mount+0x2bd/0xa30
  #1:  (&sb->s_type->i_mutex_key#9){+.+.+.}, at: [<ffffffff8110e4d3>] cgroup_remount+0x43/0x200
  #2:  (cgroup_mutex){+.+.+.}, at: [<ffffffff8110e4e1>] cgroup_remount+0x51/0x200
  #3:  (cgroup_root_mutex){+.+.+.}, at: [<ffffffff8110e4ef>] cgroup_remount+0x5f/0x200

 stack backtrace:
 CPU: 2 PID: 525 Comm: mount Not tainted 3.10.0-rc4-work+ #1
 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
  ffffffff829651f0 ffff88000ec2fc28 ffffffff81c24bb1 ffff88000ec2fce8
  ffffffff810f420d 0000000000000006 0000000000000001 0000000000000056
  ffff8800153b4640 ffff880000000000 ffffffff81c2e468 ffff8800153b4640
 Call Trace:
  [<ffffffff81c24bb1>] dump_stack+0x19/0x1b
  [<ffffffff810f420d>] __lock_acquire+0x15dd/0x1e60
  [<ffffffff810f531c>] lock_acquire+0x9c/0x1f0
  [<ffffffff81c2a805>] mutex_lock_nested+0x65/0x410
  [<ffffffff8110a3e1>] drop_parsed_module_refcounts+0x21/0xb0
  [<ffffffff8110e63e>] cgroup_remount+0x1ae/0x200
  [<ffffffff811c9bb2>] do_remount_sb+0x82/0x190
  [<ffffffff811e9d41>] do_mount+0x5f1/0xa30
  [<ffffffff811ea203>] SyS_mount+0x83/0xc0
  [<ffffffff81c2fb82>] system_call_fastpath+0x16/0x1b

Fix it by moving the drop_parsed_module_refcounts() invocation outside
cgroup_mutex.
Signed-off-by: NTejun Heo <tj@kernel.org>

kernel/cgroup.c still has places where a RCU pointer is set and
accessed directly without going through RCU_INIT_POINTER() or
rcu_dereference_protected().  They're all properly protected accesses
so nothing is broken but it leads to spurious sparse RCU address space
warnings.

Substitute direct accesses with RCU_INIT_POINTER() and
rcu_dereference_protected().  Note that %true is specified as the
extra condition for all derference updates.  This isn't ideal as all
it does is suppressing warning without actually policing
synchronization rules; however, most are scheduled to be removed
pretty soon along with css_id itself, so no reason to be more
elaborate.

Combined with the previous changes, this removes all RCU related
sparse warnings from cgroup.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Acked-by; Li Zefan <lizefan@huawei.com>

There are several places in kernel/cgroup.c where task->cgroups is
accessed and modified without going through proper RCU accessors.
None is broken as they're all lock protected accesses; however, this
still triggers sparse RCU address space warnings.

* Consistently use task_css_set() for task->cgroups dereferencing.

* Use RCU_INIT_POINTER() to clear task->cgroups to &init_css_set on
  exit.

* Remove unnecessary rcu_dereference_raw() from cset->subsys[]
  dereference in cgroup_exit().
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Acked-by: NLi Zefan <lizefan@huawei.com>

This isn't strictly necessary as all subsystems specified in
@subsys_mask are guaranteed to be pinned; however, it does spuriously
trigger lockdep warning.  Let's grab cgroup_mutex around it.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>

cgroupfs_root used to have ->actual_subsys_mask in addition to
->subsys_mask.  a8a648c4 ("cgroup: remove
cgroup->actual_subsys_mask") removed it noting that the subsys_mask is
essentially temporary and doesn't belong in cgroupfs_root; however,
the patch made it impossible to tell whether a cgroupfs_root actually
has the subsystems bound or just have the bits set leading to the
following BUG when trying to mount with subsystems which are already
mounted elsewhere.

 kernel BUG at kernel/cgroup.c:1038!
 invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
 ...
 CPU: 1 PID: 7973 Comm: mount Tainted: G        W    3.10.0-rc7-next-20130625-sasha-00011-g1c1dc0e #1105
 task: ffff880fc0ae8000 ti: ffff880fc0b9a000 task.ti: ffff880fc0b9a000
 RIP: 0010:[<ffffffff81249b29>]  [<ffffffff81249b29>] rebind_subsystems+0x409/0x5f0
 ...
 Call Trace:
  [<ffffffff8124bd4f>] cgroup_kill_sb+0xff/0x210
  [<ffffffff813d21af>] deactivate_locked_super+0x4f/0x90
  [<ffffffff8124f3b3>] cgroup_mount+0x673/0x6e0
  [<ffffffff81257169>] cpuset_mount+0xd9/0x110
  [<ffffffff813d2580>] mount_fs+0xb0/0x2d0
  [<ffffffff81404afd>] vfs_kern_mount+0xbd/0x180
  [<ffffffff814070b5>] do_new_mount+0x145/0x2c0
  [<ffffffff814085d6>] do_mount+0x356/0x3c0
  [<ffffffff8140873d>] SyS_mount+0xfd/0x140
  [<ffffffff854eb600>] tracesys+0xdd/0xe2

We still want rebind_subsystems() to take added/removed masks, so
let's fix it by marking whether a cgroupfs_root has finished binding
or not.  Also, document what's going on around ->subsys_mask
initialization so that similar mistakes aren't repeated.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-by: NSasha Levin <sasha.levin@oracle.com>
Acked-by: NLi Zefan <lizefan@huawei.com>

Before 1a574231 ("cgroup: make hierarchy_id use cyclic idr"),
hierarchy IDs were allocated from 0.  As the dummy hierarchy was
always the one first initialized, it got assigned 0 and all other
hierarchies from 1.  The patch accidentally changed the minimum
useable ID to 2.

Let's restore ID 0 for dummy_root and while at it reserve 1 for
unified hierarchy.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>
Cc: stable@vger.kernel.org