cgroup: make CONFIG_CGROUP_NET_PRIO bool and drop unnecessary init_netclassid_cgroup()

net_prio is the only cgroup which is allowed to be built as a module.
The savings from allowing one controller to be built as a module are
tiny especially given that cgroup module support itself adds quite a
bit of complexity.

Given that none of other controllers has much chance of being made a
module and that we're unlikely to add new modular controllers, the
added complexity is simply not justifiable.

As a first step to drop cgroup module support, this patch changes the
config option to bool from tristate and drops module related code from
it.

Also, while an earlier commit fe1217c4f3f7 ("net: net_cls: move
cgroupfs classid handling into core") dropped module support from
net_cls cgroup, it retained a call to cgroup_load_subsys(), which is
noop for built-in controllers.  Drop it along with
init_netclassid_cgroup().

v2: Removed modular version of task_netprioidx() in
    include/net/netprio_cgroup.h as suggested by Li Zefan.

v3: Rebased on top of fe1217c4f3f7 ("net: net_cls: move cgroupfs
    classid handling into core").  net_cls cgroup part is mostly
    dropped except for removal of init_netclassid_cgroup().

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: "David S. Miller" <davem@davemloft.net>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Thomas Graf <tgraf@suug.ch>
cgroup: drop module support

With module supported dropped from net_prio, no controller is using
cgroup module support.  None of actual resource controllers can be
built as a module and we aren't gonna add new controllers which don't
control resources.  This patch drops module support from cgroup.

* cgroup_[un]load_subsys() and cgroup_subsys->module removed.

* As there's no point in distinguishing IS_BUILTIN() and IS_MODULE(),
  cgroup_subsys.h now uses IS_ENABLED() directly.

* enum cgroup_subsys_id now exactly matches the list of enabled
  controllers as ordered in cgroup_subsys.h.

* cgroup_subsys[] is now a contiguously occupied array.  Size
  specification is no longer necessary and dropped.

* for_each_builtin_subsys() is removed and for_each_subsys() is
  updated to not require any locking.

* module ref handling is removed from rebind_subsystems().

* Module related comments dropped.

v2: Rebased on top of fe1217c4f3f7 ("net: net_cls: move cgroupfs
    classid handling into core").

v3: Added {} around the if (need_forkexit_callback) block in
    cgroup_post_fork() for readability as suggested by Li.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
cgroup: clean up cgroup_subsys names and initialization

cgroup_subsys is a bit messier than it needs to be.

* The name of a subsys can be different from its internal identifier
  defined in cgroup_subsys.h.  Most subsystems use the matching name
  but three - cpu, memory and perf_event - use different ones.

* cgroup_subsys_id enums are postfixed with _subsys_id and each
  cgroup_subsys is postfixed with _subsys.  cgroup.h is widely
  included throughout various subsystems, it doesn't and shouldn't
  have claim on such generic names which don't have any qualifier
  indicating that they belong to cgroup.

* cgroup_subsys->subsys_id should always equal the matching
  cgroup_subsys_id enum; however, we require each controller to
  initialize it and then BUG if they don't match, which is a bit
  silly.

This patch cleans up cgroup_subsys names and initialization by doing
the followings.

* cgroup_subsys_id enums are now postfixed with _cgrp_id, and each
  cgroup_subsys with _cgrp_subsys.

* With the above, renaming subsys identifiers to match the userland
  visible names doesn't cause any naming conflicts.  All non-matching
  identifiers are renamed to match the official names.

  cpu_cgroup -> cpu
  mem_cgroup -> memory
  perf -> perf_event

* controllers no longer need to initialize ->subsys_id and ->name.
  They're generated in cgroup core and set automatically during boot.

* Redundant cgroup_subsys declarations removed.

* While updating BUG_ON()s in cgroup_init_early(), convert them to
  WARN()s.  BUGging that early during boot is stupid - the kernel
  can't print anything, even through serial console and the trap
  handler doesn't even link stack frame properly for back-tracing.

This patch doesn't introduce any behavior changes.

v2: Rebased on top of fe1217c4f3f7 ("net: net_cls: move cgroupfs
    classid handling into core").

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: "David S. Miller" <davem@davemloft.net>
Acked-by: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Aristeu Rozanski <aris@redhat.com>
Acked-by: Ingo Molnar <mingo@redhat.com>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Serge E. Hallyn <serue@us.ibm.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Thomas Graf <tgraf@suug.ch>
cgroup: rename cgroup_subsys->subsys_id to ->id

It's no longer referenced outside cgroup core, so renaming is easy.
Let's rename it for consistency & brevity.

This patch is pure rename.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
cgroup: update locking in cgroup_show_options()

cgroup_show_options() grabs cgroup_root_mutex to protect the options
changing while printing; however, holding root_mutex or not doesn't
really make much difference for the function.  subsys_mask can be
atomically tested and most of the options aren't allowed to change
anyway once mounted.

The only field which needs synchronization is ->release_agent_path.
This patch introduces a dedicated spinlock to synchronize accesses to
the field and drops cgroup_root_mutex locking from
cgroup_show_options().  The next patch will remove cgroup_root_mutex.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
cgroup: remove cgroup_root_mutex

cgroup_root_mutex was added to avoid deadlock involving namespace_sem
via cgroup_show_options().  It added a lot of overhead for the small
purpose of it and, because it's nested under cgroup_mutex, it has very
limited usefulness.  The previous patch made cgroup_show_options() not
use cgroup_root_mutex, so nobody needs it anymore.  Remove it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Merge branch 'for-3.14-fixes' into for-3.15

Pending kernfs conversion depends on fixes in for-3.14-fixes.  Pull it
into for-3.15.

Signed-off-by: Tejun Heo <tj@kernel.org>
Merge branch 'driver-core-next' into cgroup/for-3.15

Pending kernfs conversion depends on kernfs improvements in
driver-core-next.  Pull it into for-3.15.

Signed-off-by: Tejun Heo <tj@kernel.org>
Merge branch 'cgroup/for-3.14-fixes' into cgroup/for-3.15

Pull for-3.14-fixes to receive 0ab02ca8f887 ("cgroup: protect
modifications to cgroup_idr with cgroup_mutex") prior to kernfs
conversion series to avoid non-trivial conflicts.

Signed-off-by: Tejun Heo <tj@kernel.org>
cgroup: improve css_from_dir() into css_tryget_from_dir()

css_from_dir() returns the matching css (cgroup_subsys_state) given a
dentry and subsystem.  The function doesn't pin the css before
returning and requires the caller to be holding RCU read lock or
cgroup_mutex and handling pinning on the caller side.

Given that users of the function are likely to want to pin the
returned css (both existing users do) and that getting and putting
css's are very cheap, there's no reason for the interface to be tricky
like this.

Rename css_from_dir() to css_tryget_from_dir() and make it try to pin
the found css and return it only if pinning succeeded.  The callers
are updated so that they no longer do RCU locking and pinning around
the function and just use the returned css.

This will also ease converting cgroup to kernfs.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
cgroup: introduce cgroup_tree_mutex

Currently cgroup uses combination of inode->i_mutex'es and
cgroup_mutex for synchronization.  With the scheduled kernfs
conversion, i_mutex'es will be removed.  Unfortunately, just using
cgroup_mutex isn't possible.  All kernfs file and syscall operations,
most of which require grabbing cgroup_mutex, will be called with
kernfs active ref held and, if we try to perform kernfs removals under
cgroup_mutex, it can deadlock as kernfs_remove() tries to drain the
target node.

Let's introduce a new outer mutex, cgroup_tree_mutex, which protects
stuff used during hierarchy changing operations - cftypes and all the
operations which may affect the cgroupfs.  It also covers css
association and iteration.  This allows cgroup_css(), for_each_css()
and other css iterators to be called under cgroup_tree_mutex.  The new
mutex will nest above both kernfs's active ref protection and
cgroup_mutex.  By protecting tree modifications with a separate outer
mutex, we can get rid of the forementioned deadlock condition.

Actual file additions and removals now require cgroup_tree_mutex
instead of cgroup_mutex.  Currently, cgroup_tree_mutex is never used
without cgroup_mutex; however, we'll soon add hierarchy modification
sections which are only protected by cgroup_tree_mutex.  In the
future, we might want to make the locking more granular by better
splitting the coverages of the two mutexes.  For now, this should do.

v2: Rebased on top of 0ab02ca8f887 ("cgroup: protect modifications to
    cgroup_idr with cgroup_mutex").

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
cgroup: release cgroup_mutex over file removals

Now that cftypes and all tree modification operations are protected by
cgroup_tree_mutex, we can drop cgroup_mutex while deleting files and
directories.  Drop cgroup_mutex over removals.

This doesn't make any noticeable difference now but is to help kernfs
conversion.  In kernfs, removals are sync points which drain in-flight
operations as those operations would grab cgroup_mutex, trying to
delete under cgroup_mutex would deadlock.  This can be resolved by
just holding the outer cgroup_tree_mutex which nests outside both
kernfs active reference and cgroup_mutex.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
cgroup: restructure locking and error handling in cgroup_mount()

cgroup is scheduled to be converted to kernfs.  After conversion,
cgroup_mount() won't use the sget() machinery for finding out existing
super_blocks but instead would do that directly.  It'll search the
existing cgroupfs_roots for a matching one and create a new one iff a
match doesn't exist.  To ease such conversion, this patch restructures
locking and error handling of the function.

cgroup_tree_mutex and cgroup_mutex are grabbed from the get-go and
held until return.  For now, due to the way vfs locks nest outside
cgroup mutexes, the two cgroup mutexes are temporarily dropped across
sget() and inode mutex locking, which looks quite ridiculous; however,
these will be removed through kernfs conversion and structuring the
code this way makes the conversion less painful.

The error goto labels are consolidated to two.  This looks unwieldy
now but the next patch will factor out creation of new root into a
separate function with accompanying error handling and it'll look a
lot better.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
cgroup: factor out cgroup_setup_root() from cgroup_mount()

Factor out new root initialization into cgroup_setup_root() from
cgroup_mount().  This makes it easier to follow and will ease kernfs
conversion.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
cgroup: update cgroup name handling

Straightforward updates to cgroup name handling in preparation of
kernfs conversion.

* cgroup_alloc_name() is updated to take const char * isntead of
  dentry * for name source.

* cgroup name formatting is separated out into cgroup_file_name().
  While at it, buffer length protection is added.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
cgroup: make cgroup_subsys->base_cftypes use cgroup_add_cftypes()

Currently, cgroup_subsys->base_cftypes registration is different from
dynamic cftypes registartion.  Instead of going through
cgroup_add_cftypes(), cgroup_init_subsys() invokes
cgroup_init_cftsets() which makes use of cgroup_subsys->base_cftset
which doesn't involve dynamic allocation.

While avoiding dynamic allocation is somewhat nice, having two
separate paths for cftypes registration is nasty, especially as we're
planning to add more operations during cftypes registration.

This patch drops cgroup_init_cftsets() and cgroup_subsys->base_cftset
and registers base_cftypes using cgroup_add_cftypes().  This is done
as a separate step in cgroup_init() instead of a part of
cgroup_init_subsys().  This is because cgroup_init_subsys() can be
called very early during boot when kmalloc() isn't available yet.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
cgroup: update the meaning of cftype->max_write_len

cftype->max_write_len is used to extend the maximum size of writes.
It's interpreted in such a way that the actual maximum size is one
less than the specified value.  The default size is defined by
CGROUP_LOCAL_BUFFER_SIZE.  Its interpretation is quite confusing - its
value is decremented by 1 and then compared for equality with max
size, which means that the actual default size is
CGROUP_LOCAL_BUFFER_SIZE - 2, which is 62 chars.

There's no point in having a limit that low.  Update its definition so
that it means the actual string length sans termination and anything
below PAGE_SIZE-1 is treated as PAGE_SIZE-1.

.max_write_len for "release_agent" is updated to PATH_MAX-1 and
cgroup_release_agent_write() is updated so that the redundant strlen()
check is removed and it uses strlcpy() instead of strcpy().
.max_write_len initializations in blk-throttle.c and cfq-iosched.c are
no longer necessary and removed.  The one in cpuset is kept unchanged
as it's an approximated value to begin with.

This will also make transition to kernfs smoother.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
cgroup: introduce cgroup_init/exit_cftypes()

Factor out cft->ss initialization into cgroup_init_cftypes() from
cgroup_add_cftypes() and add cft->ss clearing to cgroup_rm_cftypes()
through cgroup_exit_cftypes().

This doesn't make any meaningful difference now but the two new
functions will be expanded during kernfs transition.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
cgroup: introduce cgroup_ino()

mm/memory-failure.c::hwpoison_filter_task() has been reaching into
cgroup to extract the associated ino to be used as a filtering
criterion.  This is an implementation detail which shouldn't be
depended upon from outside cgroup proper and is about to change with
the scheduled kernfs conversion.

This patch introduces a proper interface to determine the associated
ino, cgroup_ino(), and updates hwpoison_filter_task() to use it
instead of reaching directly into cgroup.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
cgroup: misc preps for kernfs conversion

* Un-inline seq_css().  After kernfs conversion, the function will
  need to dereference internal data structures.

* Add cgroup_get/put_root() and replace direct super_block->s_active
  manipulatinos with them.  These will be converted to kernfs_root
  refcnting.

* Add cgroup_get/put() and replace dget/put() on cgrp->dentry with
  them.  These will be converted to kernfs refcnting.

* Update current_css_set_cg_links_read() to use cgroup_name() instead
  of reaching into the dentry name.  The end result is the same.

These changes don't make functional differences but will make
transition to kernfs easier.

v2: Rebased on top of 0ab02ca8f887 ("cgroup: protect modifications to
    cgroup_idr with cgroup_mutex").

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>