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  1. 09 Nov, 2012 3 commits
    • Tejun Heo's avatar
      cgroup: implement generic child / descendant walk macros · 574bd9f7
      Tejun Heo authored 
      Currently, cgroup doesn't provide any generic helper for walking a
given cgroup's children or descendants.  This patch adds the following
three macros.

* cgroup_for_each_child() - walk immediate children of a cgroup.

* cgroup_for_each_descendant_pre() - visit all descendants of a cgroup
  in pre-order tree traversal.

* cgroup_for_each_descendant_post() - visit all descendants of a
  cgroup in post-order tree traversal.

All three only require the user to hold RCU read lock during
traversal.  Verifying that each iterated cgroup is online is the
responsibility of the user.  When used with proper synchronization,
cgroup_for_each_descendant_pre() can be used to propagate state
updates to descendants in reliable way.  See comments for details.

v2: s/config/state/ in commit message and comments per Michal.  More
    documentation on synchronization rules.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujisu.com>
Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
      574bd9f7
    • Tejun Heo's avatar
      cgroup: use rculist ops for cgroup->children · eb6fd504
      Tejun Heo authored 
      Use RCU safe list operations for cgroup->children.  This will be used
to implement cgroup children / descendant walking which can be used by
controllers.

Note that cgroup_create() now puts a new cgroup at the end of the
->children list instead of head.  This isn't strictly necessary but is
done so that the iteration order is more conventional.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
Reviewed-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
      eb6fd504
    • Tejun Heo's avatar
      cgroup: add cgroup_subsys->post_create() · a8638030
      Tejun Heo authored 
      Currently, there's no way for a controller to find out whether a new
cgroup finished all ->create() allocatinos successfully and is
considered "live" by cgroup.

This becomes a problem later when we add generic descendants walking
to cgroup which can be used by controllers as controllers don't have a
synchronization point where it can synchronize against new cgroups
appearing in such walks.

This patch adds ->post_create().  It's called after all ->create()
succeeded and the cgroup is linked into the generic cgroup hierarchy.
This plays the counterpart of ->pre_destroy().

When used in combination with the to-be-added generic descendant
iterators, ->post_create() can be used to implement reliable state
inheritance.  It will be explained with the descendant iterators.

v2: Added a paragraph about its future use w/ descendant iterators per
    Michal.

v3: Forgot to add ->post_create() invocation to cgroup_load_subsys().
    Fixed.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
Reviewed-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
Cc: Glauber Costa <glommer@parallels.com>
      a8638030
  3. 08 Nov, 2012 1 commit
  5. 06 Nov, 2012 4 commits
  7. 05 Nov, 2012 9 commits
    • Tejun Heo's avatar
      Merge branch 'cgroup-rmdir-updates' into cgroup/for-3.8 · 1db1e31b
      Tejun Heo authored 
      Pull rmdir updates into for-3.8 so that further callback updates can
be put on top.  This pull created a trivial conflict between the
following two commits.

  8c7f6edb ("cgroup: mark subsystems with broken hierarchy support and whine if cgroups are nested for them")
  ed957793 ("cgroup: kill cgroup_subsys->__DEPRECATED_clear_css_refs")

The former added a field to cgroup_subsys and the latter removed one
from it.  They happen to be colocated causing the conflict.  Keeping
what's added and removing what's removed resolves the conflict.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      1db1e31b
    • Tejun Heo's avatar
      cgroup: make ->pre_destroy() return void · bcf6de1b
      Tejun Heo authored 
      All ->pre_destory() implementations return 0 now, which is the only
allowed return value.  Make it return void.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
      bcf6de1b
    • Michal Hocko's avatar
      hugetlb: do not fail in hugetlb_cgroup_pre_destroy · 9d093cb1
      Michal Hocko authored 
      Now that pre_destroy callbacks are called from the context where neither
any task can attach the group nor any children group can be added there
is no other way to fail from hugetlb_pre_destroy.
Signed-off-by: default avatarMichal Hocko <mhocko@suse.cz>
Reviewed-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarGlauber Costa <glommer@parallels.com>
Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      9d093cb1
    • Michal Hocko's avatar
      memcg: make mem_cgroup_reparent_charges non failing · ab5196c2
      Michal Hocko authored 
      Now that pre_destroy callbacks are called from the context where neither
any task can attach the group nor any children group can be added there
is no other way to fail from mem_cgroup_pre_destroy.
mem_cgroup_pre_destroy doesn't have to take a reference to memcg's css
because all css' are marked dead already.

tj: Remove now unused local variable @cgrp from
    mem_cgroup_reparent_charges().
Signed-off-by: default avatarMichal Hocko <mhocko@suse.cz>
Reviewed-by: default avatarGlauber Costa <glommer@parallels.com>
Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      ab5196c2
    • Tejun Heo's avatar
      cgroup: remove CGRP_WAIT_ON_RMDIR, cgroup_exclude_rmdir() and cgroup_release_and_wakeup_rmdir() · b25ed609
      Tejun Heo authored 
      CGRP_WAIT_ON_RMDIR is another kludge which was added to make cgroup
destruction rollback somewhat working.  cgroup_rmdir() used to drain
CSS references and CGRP_WAIT_ON_RMDIR and the associated waitqueue and
helpers were used to allow the task performing rmdir to wait for the
next relevant event.

Unfortunately, the wait is visible to controllers too and the
mechanism got exposed to memcg by 88703267 ("cgroup avoid permanent
sleep at rmdir").

Now that the draining and retries are gone, CGRP_WAIT_ON_RMDIR is
unnecessary.  Remove it and all the mechanisms supporting it.  Note
that memcontrol.c changes are essentially revert of 88703267
("cgroup avoid permanent sleep at rmdir").
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
Reviewed-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
Cc: Balbir Singh <bsingharora@gmail.com>
      b25ed609
    • Tejun Heo's avatar
      cgroup: deactivate CSS's and mark cgroup dead before invoking ->pre_destroy() · 1a90dd50
      Tejun Heo authored 
      Because ->pre_destroy() could fail and can't be called under
cgroup_mutex, cgroup destruction did something very ugly.

  1. Grab cgroup_mutex and verify it can be destroyed; fail otherwise.

  2. Release cgroup_mutex and call ->pre_destroy().

  3. Re-grab cgroup_mutex and verify it can still be destroyed; fail
     otherwise.

  4. Continue destroying.

In addition to being ugly, it has been always broken in various ways.
For example, memcg ->pre_destroy() expects the cgroup to be inactive
after it's done but tasks can be attached and detached between #2 and
#3 and the conditions that memcg verified in ->pre_destroy() might no
longer hold by the time control reaches #3.

Now that ->pre_destroy() is no longer allowed to fail.  We can switch
to the following.

  1. Grab cgroup_mutex and verify it can be destroyed; fail otherwise.

  2. Deactivate CSS's and mark the cgroup removed thus preventing any
     further operations which can invalidate the verification from #1.

  3. Release cgroup_mutex and call ->pre_destroy().

  4. Re-grab cgroup_mutex and continue destroying.

After this change, controllers can safely assume that ->pre_destroy()
will only be called only once for a given cgroup and, once
->pre_destroy() is called, the cgroup will stay dormant till it's
destroyed.

This removes the only reason ->pre_destroy() can fail - new task being
attached or child cgroup being created inbetween.  Error out path is
removed and ->pre_destroy() invocation is open coded in
cgroup_rmdir().

v2: cgroup_call_pre_destroy() removal moved to this patch per Michal.
    Commit message updated per Glauber.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
Reviewed-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
Cc: Glauber Costa <glommer@parallels.com>
      1a90dd50
    • Tejun Heo's avatar
      cgroup: use cgroup_lock_live_group(parent) in cgroup_create() · 976c06bc
      Tejun Heo authored 
      This patch makes cgroup_create() fail if @parent is marked removed.
This is to prepare for further updates to cgroup_rmdir() path.

Note that this change isn't strictly necessary.  cgroup can only be
created via mkdir and the removed marking and dentry removal happen
without releasing cgroup_mutex, so cgroup_create() can never race with
cgroup_rmdir().  Even after the scheduled updates to cgroup_rmdir(),
cgroup_mkdir() and cgroup_rmdir() are synchronized by i_mutex
rendering the added liveliness check unnecessary.

Do it anyway such that locking is contained inside cgroup proper and
we don't get nasty surprises if we ever grow another caller of
cgroup_create().
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
Reviewed-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
      976c06bc
    • Tejun Heo's avatar
      cgroup: kill CSS_REMOVED · e9316080
      Tejun Heo authored 
      CSS_REMOVED is one of the several contortions which were necessary to
support css reference draining on cgroup removal.  All css->refcnts
which need draining should be deactivated and verified to equal zero
atomically w.r.t. css_tryget().  If any one isn't zero, all refcnts
needed to be re-activated and css_tryget() shouldn't fail in the
process.

This was achieved by letting css_tryget() busy-loop until either the
refcnt is reactivated (failed removal attempt) or CSS_REMOVED is set
(committing to removal).

Now that css refcnt draining is no longer used, there's no need for
atomic rollback mechanism.  css_tryget() simply can look at the
reference count and fail if it's deactivated - it's never getting
re-activated.

This patch removes CSS_REMOVED and updates __css_tryget() to fail if
the refcnt is deactivated.  As deactivation and removal are a single
step now, they no longer need to be protected against css_tryget()
happening from irq context.  Remove local_irq_disable/enable() from
cgroup_rmdir().

Note that this removes css_is_removed() whose only user is VM_BUG_ON()
in memcontrol.c.  We can replace it with a check on the refcnt but
given that the only use case is a debug assert, I think it's better to
simply unexport it.

v2: Comment updated and explanation on local_irq_disable/enable()
    added per Michal Hocko.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
Reviewed-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>
      e9316080
    • Tejun Heo's avatar
      cgroup: kill cgroup_subsys->__DEPRECATED_clear_css_refs · ed957793
      Tejun Heo authored 
      2ef37d3f ("memcg: Simplify mem_cgroup_force_empty_list error
handling") removed the last user of __DEPRECATED_clear_css_refs.  This
patch removes __DEPRECATED_clear_css_refs and mechanisms to support
it.

* Conditionals dependent on __DEPRECATED_clear_css_refs removed.

* cgroup_clear_css_refs() can no longer fail.  All that needs to be
  done are deactivating refcnts, setting CSS_REMOVED and putting the
  base reference on each css.  Remove cgroup_clear_css_refs() and the
  failure path, and open-code the loops into cgroup_rmdir().

This patch keeps the two for_each_subsys() loops separate while open
coding them.  They can be merged now but there are scheduled changes
which need them to be separate, so keep them separate to reduce the
amount of churn.

local_irq_save/restore() from cgroup_clear_css_refs() are replaced
with local_irq_disable/enable() for simplicity.  This is safe as
cgroup_rmdir() is always called with IRQ enabled.  Note that this IRQ
switching is necessary to ensure that css_tryget() isn't called from
IRQ context on the same CPU while lower context is between CSS
deactivation and setting CSS_REMOVED as css_tryget() would hang
forever in such cases waiting for CSS to be re-activated or
CSS_REMOVED set.  This will go away soon.

v2: cgroup_call_pre_destroy() removal dropped per Michal.  Commit
    message updated to explain local_irq_disable/enable() conversion.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
Reviewed-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
      ed957793
  9. 04 Nov, 2012 1 commit
  11. 03 Nov, 2012 15 commits
  13. 02 Nov, 2012 7 commits
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