blkcg is very peculiar in that it allows setting and remembering
configurations for non-existent devices by maintaining separate data
structures for configuration.

This behavior is completely out of the usual norms and outright
confusing; furthermore, it uses dev_t number to match the
configuration to devices, which is unpredictable to begin with and
becomes completely unuseable if EXT_DEVT is fully used.

It is wholely unnecessary - we already have fully functional userland
mechanism to program devices being hotplugged which has full access to
device identification, connection topology and filesystem information.

Add a new struct blkio_group_conf which contains all blkcg
configurations to blkio_group and let blkio_group, which can be
created iff the associated device exists and is removed when the
associated device goes away, carry all configurations.

Note that, after this patch, all newly created blkg's will always have
the default configuration (unlimited for throttling and blkcg's weight
for propio).

This patch makes blkio_policy_node meaningless but doesn't remove it.
The next patch will.

-v2: Updated to retry after short sleep if blkg lookup/creation failed
     due to the queue being temporarily bypassed as indicated by
     -EBUSY return.  Pointed out by Vivek.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Currently both blk-throttle and cfq-iosched implement their own
blkio_group creation code in throtl_get_tg() and cfq_get_cfqg().  This
patch factors out the common code into blkg_lookup_create(), which
returns ERR_PTR value so that transitional failures due to queue
bypass can be distinguished from other failures.

* New plkio_policy_ops methods blkio_alloc_group_fn() and
  blkio_link_group_fn added.  Both are transitional and will be
  removed once the blkg management code is fully moved into
  blk-cgroup.c.

* blkio_alloc_group_fn() allocates policy-specific blkg which is
  usually a larger data structure with blkg as the first entry and
  intiailizes it.  Note that initialization of blkg proper, including
  percpu stats, is responsibility of blk-cgroup proper.

  Note that default config (weight, bps...) initialization is done
  from this method; otherwise, we end up violating locking order
  between blkcg and q locks via blkcg_get_CONF() functions.

* blkio_link_group_fn() is called under queue_lock and responsible for
  linking the blkg to the queue.  blkcg side is handled by blk-cgroup
  proper.

* The common blkg creation function is named blkg_lookup_create() and
  blkiocg_lookup_group() is renamed to blkg_lookup() for consistency.
  Also, throtl / cfq related functions are similarly [re]named for
  consistency.

This simplifies blkcg policy implementations and enables further
cleanup.

-v2: Vivek noticed that blkg_lookup_create() incorrectly tested
     blk_queue_dead() instead of blk_queue_bypass() leading a user of
     the function ending up creating a new blkg on bypassing queue.
     This is a bug introduced while relocating bypass patches before
     this one.  Fixed.

-v3: ERR_PTR patch folded into this one.  @for_root added to
     blkg_lookup_create() to allow creating root group on a bypassed
     queue during elevator switch.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Block cgroup policies are maintained in a linked list and,
theoretically, multiple policies sharing the same policy ID are
allowed.

This patch temporarily restricts one policy per plid and adds
blkio_policy[] array which indexes registered policy types by plid.
Both the restriction and blkio_policy[] array are transitional and
will be removed once API cleanup is complete.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

blkgio_group is association between a block cgroup and a queue for a
given policy.  Using opaque void * for association makes things
confusing and hinders factoring of common code.  Use request_queue *
and, if necessary, policy id instead.

This will help block cgroup API cleanup.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Elevator switch may involve changes to blkcg policies.  Implement
shoot down of blkio_groups.

Combined with the previous bypass updates, the end goal is updating
blkcg core such that it can ensure that blkcg's being affected become
quiescent and don't have any per-blkg data hanging around before
commencing any policy updates.  Until queues are made aware of the
policies that applies to them, as an interim step, all per-policy blkg
data will be shot down.

* blk-throtl doesn't need this change as it can't be disabled for a
  live queue; however, update it anyway as the scheduled blkg
  unification requires this behavior change.  This means that
  blk-throtl configuration will be unnecessarily lost over elevator
  switch.  This oddity will be removed after blkcg learns to associate
  individual policies with request_queues.

* blk-throtl dosen't shoot down root_tg.  This is to ease transition.
  Unified blkg will always have persistent root group and not shooting
  down root_tg for now eases transition to that point by avoiding
  having to update td->root_tg and is safe as blk-throtl can never be
  disabled

-v2: Vivek pointed out that group list is not guaranteed to be empty
     on return from clear function if it raced cgroup removal and
     lost.  Fix it by waiting a bit and retrying.  This kludge will
     soon be removed once locking is updated such that blkg is never
     in limbo state between blkcg and request_queue locks.

     blk-throtl no longer shoots down root_tg to avoid breaking
     td->root_tg.

     Also, Nest queue_lock inside blkio_list_lock not the other way
     around to avoid introduce possible deadlock via blkcg lock.

-v3: blkcg_clear_queue() repositioned and renamed to
     blkg_destroy_all() to increase consistency with later changes.
     cfq_clear_queue() updated to check q->elevator before
     dereferencing it to avoid NULL dereference on not fully
     initialized queues (used by later change).
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Block cgroup core can be built as module; however, it isn't too useful
as blk-throttle can only be built-in and cfq-iosched is usually the
default built-in scheduler.  Scheduled blkcg cleanup requires calling
into blkcg from block core.  To simplify that, disallow building blkcg
as module by making CONFIG_BLK_CGROUP bool.

If building blkcg core as module really matters, which I doubt, we can
revisit it after blkcg API cleanup.

-v2: Vivek pointed out that IOSCHED_CFQ was incorrectly updated to
     depend on BLK_CGROUP.  Fixed.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

put_io_context() performed a complex trylock dancing to avoid
deferring ioc release to workqueue.  It was also broken on UP because
trylock was always assumed to succeed which resulted in unbalanced
preemption count.

While there are ways to fix the UP breakage, even the most
pathological microbench (forced ioc allocation and tight fork/exit
loop) fails to show any appreciable performance benefit of the
optimization.  Strip it out.  If there turns out to be workloads which
are affected by this change, simpler optimization from the discussion
thread can be applied later.
Signed-off-by: NTejun Heo <tj@kernel.org>
LKML-Reference: <1328514611.21268.66.camel@sli10-conroe>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

cic is association between io_context and request_queue.  A cic is
linked from both ioc and q and should be destroyed when either one
goes away.  As ioc and q both have their own locks, locking becomes a
bit complex - both orders work for removal from one but not from the
other.

Currently, cfq tries to circumvent this locking order issue with RCU.
ioc->lock nests inside queue_lock but the radix tree and cic's are
also protected by RCU allowing either side to walk their lists without
grabbing lock.

This rather unconventional use of RCU quickly devolves into extremely
fragile convolution.  e.g. The following is from cfqd going away too
soon after ioc and q exits raced.

 general protection fault: 0000 [#1] PREEMPT SMP
 CPU 2
 Modules linked in:
 [   88.503444]
 Pid: 599, comm: hexdump Not tainted 3.1.0-rc10-work+ #158 Bochs Bochs
 RIP: 0010:[<ffffffff81397628>]  [<ffffffff81397628>] cfq_exit_single_io_context+0x58/0xf0
 ...
 Call Trace:
  [<ffffffff81395a4a>] call_for_each_cic+0x5a/0x90
  [<ffffffff81395ab5>] cfq_exit_io_context+0x15/0x20
  [<ffffffff81389130>] exit_io_context+0x100/0x140
  [<ffffffff81098a29>] do_exit+0x579/0x850
  [<ffffffff81098d5b>] do_group_exit+0x5b/0xd0
  [<ffffffff81098de7>] sys_exit_group+0x17/0x20
  [<ffffffff81b02f2b>] system_call_fastpath+0x16/0x1b

The only real hot path here is cic lookup during request
initialization and avoiding extra locking requires very confined use
of RCU.  This patch makes cic removal from both ioc and request_queue
perform double-locking and unlink immediately.

* From q side, the change is almost trivial as ioc->lock nests inside
  queue_lock.  It just needs to grab each ioc->lock as it walks
  cic_list and unlink it.

* From ioc side, it's a bit more difficult because of inversed lock
  order.  ioc needs its lock to walk its cic_list but can't grab the
  matching queue_lock and needs to perform unlock-relock dancing.

  Unlinking is now wholly done from put_io_context() and fast path is
  optimized by using the queue_lock the caller already holds, which is
  by far the most common case.  If the ioc accessed multiple devices,
  it tries with trylock.  In unlikely cases of fast path failure, it
  falls back to full double-locking dance from workqueue.

Double-locking isn't the prettiest thing in the world but it's *far*
simpler and more understandable than RCU trick without adding any
meaningful overhead.

This still leaves a lot of now unnecessary RCU logics.  Future patches
will trim them.

-v2: Vivek pointed out that cic->q was being dereferenced after
     cic->release() was called.  Updated to use local variable @this_q
     instead.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

ioprio/cgroup change was handled by marking the changed state in ioc
and, on the following access to the ioc, performing RCU-protected
iteration through all cic's grabbing the matching queue_lock.

This patch moves the changed state to each cic.  When ioprio or cgroup
changes, the respective bit is set on all cic's of the ioc and when
each of those cic (not ioc) is accessed, change is applied for that
specific ioc-queue pair.

This also fixes the following two race conditions between setting and
clearing of changed states.

* Missing barrier between assign/load of ioprio and ioprio_changed
  allowed applying old ioprio.

* Change requests could happen between application of change and
  clearing of changed variables.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Ignoring copy_io() during fork, io_context can be allocated from two
places - current_io_context() and set_task_ioprio().  The former is
always called from local task while the latter can be called from
different task.  The synchornization between them are peculiar and
dubious.

* current_io_context() doesn't grab task_lock() and assumes that if it
  saw %NULL ->io_context, it would stay that way until allocation and
  assignment is complete.  It has smp_wmb() between alloc/init and
  assignment.

* set_task_ioprio() grabs task_lock() for assignment and does
  smp_read_barrier_depends() between "ioc = task->io_context" and "if
  (ioc)".  Unfortunately, this doesn't achieve anything - the latter
  is not a dependent load of the former.  ie, if ioc itself were being
  dereferenced "ioc->xxx", it would mean something (not sure what tho)
  but as the code currently stands, the dependent read barrier is
  noop.

As only one of the the two test-assignment sequences is task_lock()
protected, the task_lock() can't do much about race between the two.
Nothing prevents current_io_context() and set_task_ioprio() allocating
its own ioc for the same task and overwriting the other's.

Also, set_task_ioprio() can race with exiting task and create a new
ioc after exit_io_context() is finished.

ioc get/put doesn't have any reason to be complex.  The only hot path
is accessing the existing ioc of %current, which is simple to achieve
given that ->io_context is never destroyed as long as the task is
alive.  All other paths can happily go through task_lock() like all
other task sub structures without impacting anything.

This patch updates ioc get/put so that it becomes more conventional.

* alloc_io_context() is replaced with get_task_io_context().  This is
  the only interface which can acquire access to ioc of another task.
  On return, the caller has an explicit reference to the object which
  should be put using put_io_context() afterwards.

* The functionality of current_io_context() remains the same but when
  creating a new ioc, it shares the code path with
  get_task_io_context() and always goes through task_lock().

* get_io_context() now means incrementing ref on an ioc which the
  caller already has access to (be that an explicit refcnt or implicit
  %current one).

* PF_EXITING inhibits creation of new io_context and once
  exit_io_context() is finished, it's guaranteed that both ioc
  acquisition functions return %NULL.

* All users are updated.  Most are trivial but
  smp_read_barrier_depends() removal from cfq_get_io_context() needs a
  bit of explanation.  I suppose the original intention was to ensure
  ioc->ioprio is visible when set_task_ioprio() allocates new
  io_context and installs it; however, this wouldn't have worked
  because set_task_ioprio() doesn't have wmb between init and install.
  There are other problems with this which will be fixed in another
  patch.

* While at it, use NUMA_NO_NODE instead of -1 for wildcard node
  specification.

-v2: Vivek spotted contamination from debug patch.  Removed.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Now that subsys->can_attach() and attach() take @tset instead of
@task, they can handle per-task operations.  Convert
->can_attach_task() and ->attach_task() users to use ->can_attach()
and attach() instead.  Most converions are straight-forward.
Noteworthy changes are,

* In cgroup_freezer, remove unnecessary NULL assignments to unused
  methods.  It's useless and very prone to get out of sync, which
  already happened.

* In cpuset, PF_THREAD_BOUND test is checked for each task.  This
  doesn't make any practical difference but is conceptually cleaner.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reviewed-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: NFrederic Weisbecker <fweisbec@gmail.com>
Acked-by: NLi Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <paul@paulmenage.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: James Morris <jmorris@namei.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>

blkcg->policy_list is protected by blkcg->lock. Its not rcu protected
list. So even for readers, they need to take blkcg->lock. There are
few functions which were reading the list without taking lock. Fix it.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

If a rule is being deleted, free up associated policy node. Otherwise
that memory is leaked.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

blkio_policy_parse_and_set() calls blkio_check_dev_num() to check
whether the given dev_t is valid.  blkio_check_dev_num() uses
get_gendisk() for verification but never puts the returned genhd
leaking the reference.

This patch collapses blkio_check_dev_num() into its caller and updates
it such that the genhd is put before returning.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

The bug is we're not able to remove the device from blkio cgroup's
per-device control files if it gets unplugged.

To reproduce the bug:

  # mount -t cgroup -o blkio xxx /cgroup
  # cd /cgroup
  # echo "8:0 1000" > blkio.throttle.read_bps_device
  # unplug the device
  # cat blkio.throttle.read_bps_device
  8:0	1000
  # echo "8:0 0" > blkio.throttle.read_bps_device
  -bash: echo: write error: No such device

After patching, the device removal will succeed.

Thanks for the comments of Paul, Zefan, and Vivek.
Signed-off-by: NWanlong Gao <gaowanlong@cn.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <paul@paulmenage.org>
Acked-by: NVivek Goyal <vgoyal@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: <stable@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Add cgroup subsystem callbacks for per-thread attachment in atomic contexts

Add can_attach_task(), pre_attach(), and attach_task() as new callbacks
for cgroups's subsystem interface.  Unlike can_attach and attach, these
are for per-thread operations, to be called potentially many times when
attaching an entire threadgroup.

Also, the old "bool threadgroup" interface is removed, as replaced by
this.  All subsystems are modified for the new interface - of note is
cpuset, which requires from/to nodemasks for attach to be globally scoped
(though per-cpuset would work too) to persist from its pre_attach to
attach_task and attach.

This is a pre-patch for cgroup-procs-writable.patch.
Signed-off-by: NBen Blum <bblum@andrew.cmu.edu>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Reviewed-by: NPaul Menage <menage@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Make BLKIO_STAT_MERGED per cpu hence gettring rid of need of taking
blkg->stats_lock.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

Now dispatch stats update is lock free. But reset of these stats still
takes blkg->stats_lock and is dependent on that. As stats are per cpu,
we should be able to just reset the stats on each cpu without any locks.
(Atleast for 64bit arch).

On 32bit arch there is a small race where 64bit updates are not atomic.
The result of this race can be that in the presence of other writers,
one might not get 0 value after reset of a stat and might see something
intermediate

One can write more complicated code to cover this race like sending IPI
to other cpus to reset stats and for offline cpus, reset these directly.

Right not I am not taking that path because reset_update is more of a
debug feature and it can happen only on 32bit arch and possibility of
it happening is small. Will fix it if it becomes a real problem. For
the time being going for code simplicity.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

Some of the stats are 64bit and updation will be non atomic on 32bit
architecture. Use sequence counters on 32bit arch to make reading
of stats safe.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

Currently we take blkg_stat lock for even updating the stats. So even if
a group has no throttling rules (common case for root group), we end
up taking blkg_lock, for updating the stats.

Make dispatch stats per cpu so that these can be updated without taking
blkg lock.

If cpu goes offline, these stats simply disappear. No protection has
been provided for that yet. Do we really need anything for that?
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

cgroup unaccounted_time file is created only if CONFIG_DEBUG_BLK_CGROUP=y.
there are some fields which are out side this config option. Fix that.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

Currentlly we first map the task to cgroup and then cgroup to
blkio_cgroup. There is a more direct way to get to blkio_cgroup
from task using task_subsys_state(). Use that.

The real reason for the fix is that it also avoids a race in generic
cgroup code. During remount/umount rebind_subsystems() is called and
it can do following with and rcu protection.

cgrp->subsys[i] = NULL;

That means if somebody got hold of cgroup under rcu and then it tried
to do cgroup->subsys[] to get to blkio_cgroup, it would get NULL which
is wrong. I was running into this race condition with ltp running on a
upstream derived kernel and that lead to crash.

So ideally we should also fix cgroup generic code to wait for rcu
grace period before setting pointer to NULL. Li Zefan is not very keen
on introducing synchronize_wait() as he thinks it will slow
down moun/remount/umount operations.

So for the time being atleast fix the kernel crash by taking a more
direct route to blkio_cgroup.

One tester had reported a crash while running LTP on a derived kernel
and with this fix crash is no more seen while the test has been
running for over 6 days.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Reviewed-by: NLi Zefan <lizf@cn.fujitsu.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

Fixes generated by 'codespell' and manually reviewed.
Signed-off-by: NLucas De Marchi <lucas.demarchi@profusion.mobi>

This change moves unaccounted_time to only be reported when
CONFIG_DEBUG_BLK_CGROUP is true.
Signed-off-by: NJustin TerAvest <teravest@google.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

There are two kind of times that tasks are not charged for: the first
seek and the extra time slice used over the allocated timeslice. Both
of these exported as a new unaccounted_time stat.

I think it would be good to have this reported in 'time' as well, but
that is probably a separate discussion.
Signed-off-by: NJustin TerAvest <teravest@google.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

o Allow hierarchical cgroup creation for blkio controller

o Currently we disallow it as both the io controller policies (throttling
  as well as proportion bandwidth) do not support hierarhical accounting
  and control. But the flip side is that blkio controller can not be used with
  libvirt as libvirt creates a cgroup hierarchy deeper than 1 level.

  <top-level-cgroup-dir>/<controller>/libvirt/qemu/<virtual-machine-groups>

o So this patch will allow creation of cgroup hierarhcy but at the backend
  everything will be treated as flat. So if somebody created a an hierarchy
  like as follows.

			root
			/  \
		     test1 test2
			|
		     test3

  CFQ and throttling will practically treat all groups at same level.

				pivot
			     /  |   \  \
			root  test1 test2  test3

o Once we have actual support for hierarchical accounting and control
  then we can introduce another cgroup tunable file "blkio.use_hierarchy"
  which will be 0 by default but if user wants to enforce hierarhical
  control then it can be set to 1. This way there should not be any
  ABI problems down the line.

o The only not so pretty part is introduction of extra file "use_hierarchy"
  down the line. Kame-san had mentioned that hierarhical accounting is
  expensive in memory controller hence they keep it off by default. I
  suspect same will be the case for IO controller also as for each IO
  completion we shall have to account IO through hierarchy up to the root.
  if yes, then it probably is not a very bad idea to introduce this extra
  file so that it will be used only when somebody needs it and some people
  might enable hierarchy only in part of the hierarchy.

o This is how basically memory controller also uses "use_hierarhcy" and
  they also allowed creation of hierarchies when actual backend support
  was not available.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Acked-by: NBalbir Singh <balbir@linux.vnet.ibm.com>
Reviewed-by: NGui Jianfeng <guijianfeng@cn.fujitsu.com>
Reviewed-by: NCiju Rajan K <ciju@linux.vnet.ibm.com>
Tested-by: NCiju Rajan K <ciju@linux.vnet.ibm.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

- Limit max iops value to UINT_MAX and return error to user if value is more
  than that instead of accepting bigger values and truncating implicitly.
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

o Currently any cgroup throttle limit changes are processed asynchronousy and
  the change does not take affect till a new bio is dispatched from same group.

o It might happen that a user sets a redicuously low limit on throttling.
  Say 1 bytes per second on reads. In such cases simple operations like mount
  a disk can wait for a very long time.

o Once bio is throttled, there is no easy way to come out of that wait even if
  user increases the read limit later.

o This patch fixes it. Now if a user changes the cgroup limits, we recalculate
  the bio dispatch time according to new limits.

o Can't take queueu lock under blkcg_lock, hence after the change I wake
  up the dispatch thread again which recalculates the time. So there are some
  variables being synchronized across two threads without lock and I had to
  make use of barriers. Hoping I have used barriers correctly. Any review of
  memory barrier code especially will help.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

o Now a cgroup list of blkg elements can contain blkg from multiple policies.
  Before sending an unlink event, make sure blkg belongs to they policy. If
  policy does not own the blkg, do not send update for this blkg.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

Currently throttling related files were visible even if user had disabled
throttling using config options. It was switching off background throttling
of bio but not the cgroup files. This patch fixes it.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

o cgroup changes for IOPS throttling rules.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

o cgroup chagnes for throttle policy.

o Introduces READ and WRITE bytes per second throttling rules.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

o This patch prepares the base for introducing new IO control policies.
  Currently all the code is written knowing there is only one policy
  and that is proportional bandwidth. Creating infrastructure for newer
  policies to come in.

o Also there were many functions which were generated using macro. It was
  very confusing. Got rid of those.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

o Kill extra "dev weight" header which is printed when somebody reads
  blkio.weight_device file. This really seems to be out of convention. No other
  blkio files are printing any header at the start of file. I think it is ok
  to just print values and how to interpret values should be part of
  documentation.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

If the cgroup hierarchy for blkio control groups is deeper than two
levels, kernel should not allow the creation of further levels. mkdir
system call does not except EINVAL as a return value. This patch
replaces EINVAL with more appropriate EPERM
Signed-off-by: NCiju Rajan K <ciju@linux.vnet.ibm.com>
Reviewed-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

with CONFIG_PROVE_RCU=y, a warning can be triggered:

  # mount -t cgroup -o blkio xxx /mnt
  # mkdir /mnt/subgroup

...
kernel/cgroup.c:4442 invoked rcu_dereference_check() without protection!
...

To fix this, we avoid caling css_depth() here, which is a bit simpler
than the original code.
Signed-off-by: NLi Zefan <lizf@cn.fujitsu.com>
Acked-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>

goto has its place, but lets cut back on some of the more
frivolous uses of it.
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>

This patch fixes few usability and configurability issues.

o All the cgroup based controller options are configurable from
  "Genral Setup/Control Group Support/" menu. blkio is the only exception.
  Hence make this option visible in above menu and make it configurable from
  there to bring it inline with rest of the cgroup based controllers.

o Get rid of CONFIG_DEBUG_CFQ_IOSCHED.

  This option currently does two things.

  - Enable printing of cgroup paths in blktrace
  - Enables CONFIG_DEBUG_BLK_CGROUP, which in turn displays additional stat
    files in cgroup.

  If we are using group scheduling, blktrace data is of not really much use
  if cgroup information is not present. To get this data, currently one has to
  also enable CONFIG_DEBUG_CFQ_IOSCHED, which in turn brings the overhead of
  all the additional debug stat files which is not desired.

  Hence, this patch moves printing of cgroup paths under
  CONFIG_CFQ_GROUP_IOSCHED.

  This allows us to get rid of CONFIG_DEBUG_CFQ_IOSCHED completely. Now all
  the debug stat files are controlled only by CONFIG_DEBUG_BLK_CGROUP which
  can be enabled through config menu.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Acked-by: NDivyesh Shah <dpshah@google.com>
Reviewed-by: NGui Jianfeng <guijianfeng@cn.fujitsu.com>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>

o Once in a while, I was hitting a BUG_ON() in blkio code. empty_time was
  assuming that upon slice expiry, group can't be marked empty already (except
  forced dispatch).

  But this assumption is broken if cfqq can move (group_isolation=0) across
  groups after receiving a request.

  I think most likely in this case we got a request in a cfqq and accounted
  the rq in one group, later while adding the cfqq to tree, we moved the queue
  to a different group which was already marked empty and after dispatch from
  slice we found group already marked empty and raised alarm.

  This patch does not error out if group is already marked empty. This can
  introduce some empty_time stat error only in case of group_isolation=0. This
  is better than crashing. In case of group_isolation=1 we should still get
  same stats as before this patch.

[  222.308546] ------------[ cut here ]------------
[  222.309311] kernel BUG at block/blk-cgroup.c:236!
[  222.309311] invalid opcode: 0000 [#1] SMP
[  222.309311] last sysfs file: /sys/devices/virtual/block/dm-3/queue/scheduler
[  222.309311] CPU 1
[  222.309311] Modules linked in: dm_round_robin dm_multipath qla2xxx scsi_transport_fc dm_zero dm_mirror dm_region_hash dm_log dm_mod [last unloaded: scsi_wait_scan]
[  222.309311]
[  222.309311] Pid: 4780, comm: fio Not tainted 2.6.34-rc4-blkio-config #68 0A98h/HP xw8600 Workstation
[  222.309311] RIP: 0010:[<ffffffff8121ad88>]  [<ffffffff8121ad88>] blkiocg_set_start_empty_time+0x50/0x83
[  222.309311] RSP: 0018:ffff8800ba6e79f8  EFLAGS: 00010002
[  222.309311] RAX: 0000000000000082 RBX: ffff8800a13b7990 RCX: ffff8800a13b7808
[  222.309311] RDX: 0000000000002121 RSI: 0000000000000082 RDI: ffff8800a13b7a30
[  222.309311] RBP: ffff8800ba6e7a18 R08: 0000000000000000 R09: 0000000000000001
[  222.309311] R10: 000000000002f8c8 R11: ffff8800ba6e7ad8 R12: ffff8800a13b78ff
[  222.309311] R13: ffff8800a13b7990 R14: 0000000000000001 R15: ffff8800a13b7808
[  222.309311] FS:  00007f3beec476f0(0000) GS:ffff880001e40000(0000) knlGS:0000000000000000
[  222.309311] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  222.309311] CR2: 000000000040e7f0 CR3: 00000000a12d5000 CR4: 00000000000006e0
[  222.309311] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  222.309311] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[  222.309311] Process fio (pid: 4780, threadinfo ffff8800ba6e6000, task ffff8800b3d6bf00)
[  222.309311] Stack:
[  222.309311]  0000000000000001 ffff8800bab17a48 ffff8800bab17a48 ffff8800a13b7800
[  222.309311] <0> ffff8800ba6e7a68 ffffffff8121da35 ffff880000000001 00ff8800ba5c5698
[  222.309311] <0> ffff8800ba6e7a68 ffff8800a13b7800 0000000000000000 ffff8800bab17a48
[  222.309311] Call Trace:
[  222.309311]  [<ffffffff8121da35>] __cfq_slice_expired+0x2af/0x3ec
[  222.309311]  [<ffffffff8121fd7b>] cfq_dispatch_requests+0x2c8/0x8e8
[  222.309311]  [<ffffffff8120f1cd>] ? spin_unlock_irqrestore+0xe/0x10
[  222.309311]  [<ffffffff8120fb1a>] ? blk_insert_cloned_request+0x70/0x7b
[  222.309311]  [<ffffffff81210461>] blk_peek_request+0x191/0x1a7
[  222.309311]  [<ffffffffa0002799>] dm_request_fn+0x38/0x14c [dm_mod]
[  222.309311]  [<ffffffff810ae61f>] ? sync_page_killable+0x0/0x35
[  222.309311]  [<ffffffff81210fd4>] __generic_unplug_device+0x32/0x37
[  222.309311]  [<ffffffff81211274>] generic_unplug_device+0x2e/0x3c
[  222.309311]  [<ffffffffa00011a6>] dm_unplug_all+0x42/0x5b [dm_mod]
[  222.309311]  [<ffffffff8120ca37>] blk_unplug+0x29/0x2d
[  222.309311]  [<ffffffff8120ca4d>] blk_backing_dev_unplug+0x12/0x14
[  222.309311]  [<ffffffff81109a7a>] block_sync_page+0x35/0x39
[  222.309311]  [<ffffffff810ae616>] sync_page+0x41/0x4a
[  222.309311]  [<ffffffff810ae62d>] sync_page_killable+0xe/0x35
[  222.309311]  [<ffffffff8158aa59>] __wait_on_bit_lock+0x46/0x8f
[  222.309311]  [<ffffffff810ae4f5>] __lock_page_killable+0x66/0x6d
[  222.309311]  [<ffffffff81056f9c>] ? wake_bit_function+0x0/0x33
[  222.309311]  [<ffffffff810ae528>] lock_page_killable+0x2c/0x2e
[  222.309311]  [<ffffffff810afbc5>] generic_file_aio_read+0x361/0x4f0
[  222.309311]  [<ffffffff810ea044>] do_sync_read+0xcb/0x108
[  222.309311]  [<ffffffff811e42f7>] ? security_file_permission+0x16/0x18
[  222.309311]  [<ffffffff810ea6ab>] vfs_read+0xab/0x108
[  222.309311]  [<ffffffff810ea7c8>] sys_read+0x4a/0x6e
[  222.309311]  [<ffffffff81002b5b>] system_call_fastpath+0x16/0x1b
[  222.309311] Code: 58 01 00 00 00 48 89 c6 75 0a 48 83 bb 60 01 00 00 00 74 09 48 8d bb a0 00 00 00 eb 35 41 fe cc 74 0d f6 83 c0 01 00 00 04 74 04 <0f> 0b eb fe 48 89 75 e8 e8 be e0 de ff 66 83 8b c0 01 00 00 04
[  222.309311] RIP  [<ffffffff8121ad88>] blkiocg_set_start_empty_time+0x50/0x83
[  222.309311]  RSP <ffff8800ba6e79f8>
[  222.309311] ---[ end trace 32b4f71dffc15712 ]---
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Acked-by: NDivyesh Shah <dpshah@google.com>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>

This fixes the lockdep warning reported by Gui Jianfeng.
Signed-off-by: NDivyesh Shah <dpshah@google.com>
Reviewed-by: NGui Jianfeng <guijianfeng@cn.fujitsu.com>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>