cgroup_cfts_commit() uses dget() to keep cgroup alive after cgroup_mutex
is dropped, but dget() won't prevent cgroupfs from being umounted. When
the race happens, vfs will see some dentries with non-zero refcnt while
umount is in process.
Keep running this:
mount -t cgroup -o blkio xxx /cgroup
umount /cgroup
And this:
modprobe cfq-iosched
rmmod cfs-iosched
After a while, the BUG() in shrink_dcache_for_umount_subtree() may
be triggered:
BUG: Dentry xxx{i=0,n=blkio.yyy} still in use (1) [umount of cgroup cgroup]
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org
cgroup's rename(2) isn't a proper migration implementation - it can't
move the cgroup to a different parent in the hierarchy. All it can do
is swapping the name string for that cgroup. This isn't useful and
can mislead users to think that cgroup supports proper cgroup-level
migration. Disallow rename(2) if sane_behavior.
v2: Fail with -EPERM instead of -EINVAL so that it matches the vfs
return value when ->rename is not implemented as suggested by Li.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
f12dc02014 ("cgroup: mark "tasks" cgroup file as insane") and
cc5943a781 ("cgroup: mark "notify_on_release" and "release_agent"
cgroup files insane") forgot to update the changed behavior
documentation in cgroup.h. Update it.
Signed-off-by: Tejun Heo <tj@kernel.org>
A css (cgroup_subsys_state) is how each cgroup is represented to a
controller. As such, it can be used in hot paths across the various
subsystems different controllers are associated with.
One of the common operations is reference counting, which up until now
has been implemented using a global atomic counter and can have
significant adverse impact on scalability. For example, css refcnt
can be gotten and put multiple times by blkcg for each IO request.
For highops configurations which try to do as much per-cpu as
possible, the global frequent refcnting can be very expensive.
In general, given the various and hugely diverse paths css's end up
being used from, we need to make it cheap and highly scalable. In its
usage, css refcnting isn't very different from module refcnting.
This patch converts css refcnting to use the recently added
percpu_ref. css_get/tryget/put() directly maps to the matching
percpu_ref operations and the deactivation logic is no longer
necessary as percpu_ref already has refcnt killing.
The only complication is that as the refcnt is per-cpu,
percpu_ref_kill() in itself doesn't ensure that further tryget
operations will fail, which we need to guarantee before invoking
->css_offline()'s. This is resolved collecting kill confirmation
using percpu_ref_kill_and_confirm() and initiating the offline phase
of destruction after all css refcnt's are confirmed to be seen as
killed on all CPUs. The previous patches already splitted destruction
into two phases, so percpu_ref_kill_and_confirm() can be hooked up
easily.
This patch removes css_refcnt() which is used for rcu dereference
sanity check in css_id(). While we can add a percpu refcnt API to ask
the same question, css_id() itself is scheduled to be removed fairly
soon, so let's not bother with it. Just drop the sanity check and use
rcu_dereference_raw() instead.
v2: - init_cgroup_css() was calling percpu_ref_init() without checking
the return value. This causes two problems - the obvious lack
of error handling and percpu_ref_init() being called from
cgroup_init_subsys() before the allocators are up, which
triggers warnings but doesn't cause actual problems as the
refcnt isn't used for roots anyway. Fix both by moving
percpu_ref_init() to cgroup_create().
- The base references were put too early by
percpu_ref_kill_and_confirm() and cgroup_offline_fn() put the
refs one extra time. This wasn't noticeable because css's go
through another RCU grace period before being freed. Update
cgroup_destroy_locked() to grab an extra reference before
killing the refcnts. This problem was noticed by Kent.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Kent Overstreet <koverstreet@google.com>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: "Alasdair G. Kergon" <agk@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Glauber Costa <glommer@gmail.com>
Split cgroup_destroy_locked() into two steps and put the latter half
into cgroup_offline_fn() which is executed from a work item. The
latter half is responsible for offlining the css's, removing the
cgroup from internal lists, and propagating release notification to
the parent. The separation is to allow using percpu refcnt for css.
Note that this allows for other cgroup operations to happen between
the first and second halves of destruction, including creating a new
cgroup with the same name. As the target cgroup is marked DEAD in the
first half and cgroup internals don't care about the names of cgroups,
this should be fine. A comment explaining this will be added by the
next patch which implements the actual percpu refcnting.
As RCU freeing is guaranteed to happen after the second step of
destruction, we can use the same work item for both. This patch
renames cgroup->free_work to ->destroy_work and uses it for both
purposes. INIT_WORK() is now performed right before queueing the work
item.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This patch reorders the operations in cgroup_destroy_locked() such
that the userland visible parts happen before css offlining and
removal from the ->sibling list. This will be used to make css use
percpu refcnt.
While at it, split out CGRP_DEAD related comment from the refcnt
deactivation one and correct / clarify how different guarantees are
met.
While this patch changes the specific order of operations, it
shouldn't cause any noticeable behavior difference.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Implement percpu_tryget() which stops giving out references once the
percpu_ref is visible as killed. Because the refcnt is per-cpu,
different CPUs will start to see a refcnt as killed at different
points in time and tryget() may continue to succeed on subset of cpus
for a while after percpu_ref_kill() returns.
For use cases where it's necessary to know when all CPUs start to see
the refcnt as dead, percpu_ref_kill_and_confirm() is added. The new
function takes an extra argument @confirm_kill which is invoked when
the refcnt is guaranteed to be viewed as killed on all CPUs.
While this isn't the prettiest interface, it doesn't force synchronous
wait and is much safer than requiring the caller to do its own
call_rcu().
v2: Patch description rephrased to emphasize that tryget() may
continue to succeed on some CPUs after kill() returns as suggested
by Kent.
v3: Function comment in percpu_ref_kill_and_confirm() updated warning
people to not depend on the implied RCU grace period from the
confirm callback as it's an implementation detail.
Signed-off-by: Tejun Heo <tj@kernel.org>
Slightly-Grumpily-Acked-by: Kent Overstreet <koverstreet@google.com>
Normally, percpu_ref_init() initializes and percpu_ref_kill()
initiates destruction which completes asynchronously. The
asynchronous destruction can be problematic in init failure path where
the caller wants to destroy half-constructed object - distinguishing
half-constructed objects from the usual release method can be painful
for complex objects.
This patch implements percpu_ref_cancel_init() which synchronously
destroys the percpu_ref without invoking release. To avoid
unintentional misuses, the function requires the ref to have finished
percpu_ref_init() but never used and triggers WARN otherwise.
v2: Explain the weird name and usage restriction in the function
comment.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Kent Overstreet <koverstreet@google.com>
Two small changes.
* Unlike most init functions, percpu_ref_init() allocates memory and
may fail. Let's mark it with __must_check in case the caller
forgets.
* percpu_ref_kill_rcu() is unnecessarily using ACCESS_ONCE() to
dereference @ref->pcpu_count, which can be misleading. The pointer
is guaranteed to be valid and visible and can't change underneath
the function. Drop ACCESS_ONCE().
Signed-off-by: Tejun Heo <tj@kernel.org>
cgroup->count tracks the number of css_sets associated with the cgroup
and used only to verify that no css_set is associated when the cgroup
is being destroyed. It's superflous as the destruction path can
simply check whether cgroup->cset_links is empty instead.
Drop cgroup->count and check ->cset_links directly from
cgroup_destroy_locked().
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
__put_css_set() does RCU read access on @cgrp across dropping
@cgrp->count so that it can continue accessing @cgrp even if the count
reached zero and destruction of the cgroup commenced. Given that both
sides - __css_put() and cgroup_destroy_locked() - are cold paths, this
is unnecessary. Just making cgroup_destroy_locked() grab css_set_lock
while checking @cgrp->count is enough.
Remove the RCU read locking from __put_css_set() and make
cgroup_destroy_locked() read-lock css_set_lock when checking
@cgrp->count. This will also allow removing @cgrp->count.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
We will add another flag indicating that the cgroup is in the process
of being killed. REMOVING / REMOVED is more difficult to distinguish
and cgroup_is_removing()/cgroup_is_removed() are a bit awkward. Also,
later percpu_ref usage will involve "kill"ing the refcnt.
s/CGRP_REMOVED/CGRP_DEAD/
s/cgroup_is_removed()/cgroup_is_dead()
This patch is purely cosmetic.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
* __css_get() isn't used by anyone. Fold it into css_get().
* Add proper function comments to all css reference functions.
This patch is purely cosmetic.
v2: Typo fix as per Li.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
There's no point in using kmalloc() instead of the clearing variant
for trivial stuff. We can live dangerously elsewhere. Use kzalloc()
instead and drop 0 inits.
While at it, do trivial code reorganization in cgroup_file_open().
This patch doesn't introduce any functional changes.
v2: I was caught in the very distant past where list_del() didn't
poison and the initial version converted list_del()s to
list_del_init()s too. Li and Kent took me out of the stasis
chamber.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Kent Overstreet <koverstreet@google.com>
Acked-by: Li Zefan <lizefan@huawei.com>
cgroups and css_sets are mapped M:N and this M:N mapping is
represented by struct cg_cgroup_link which forms linked lists on both
sides. The naming around this mapping is already confusing and struct
cg_cgroup_link exacerbates the situation quite a bit.
>From cgroup side, it starts off ->css_sets and runs through
->cgrp_link_list. From css_set side, it starts off ->cg_links and
runs through ->cg_link_list. This is rather reversed as
cgrp_link_list is used to iterate css_sets and cg_link_list cgroups.
Also, this is the only place which is still using the confusing "cg"
for css_sets. This patch cleans it up a bit.
* s/cgroup->css_sets/cgroup->cset_links/
s/css_set->cg_links/css_set->cgrp_links/
s/cgroup_iter->cg_link/cgroup_iter->cset_link/
* s/cg_cgroup_link/cgrp_cset_link/
* s/cgrp_cset_link->cg/cgrp_cset_link->cset/
s/cgrp_cset_link->cgrp_link_list/cgrp_cset_link->cset_link/
s/cgrp_cset_link->cg_link_list/cgrp_cset_link->cgrp_link/
* s/init_css_set_link/init_cgrp_cset_link/
s/free_cg_links/free_cgrp_cset_links/
s/allocate_cg_links/allocate_cgrp_cset_links/
* s/cgl[12]/link[12]/ in compare_css_sets()
* s/saved_link/tmp_link/ s/tmp/tmp_links/ and a couple similar
adustments.
* Comment and whiteline adjustments.
After the changes, we have
list_for_each_entry(link, &cont->cset_links, cset_link) {
struct css_set *cset = link->cset;
instead of
list_for_each_entry(link, &cont->css_sets, cgrp_link_list) {
struct css_set *cset = link->cg;
This patch is purely cosmetic.
v2: Fix broken sentences in the patch description.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
cgroup.c uses @cg for most struct css_set variables, which in itself
could be a bit confusing, but made much worse by the fact that there
are places which use @cg for struct cgroup variables.
compare_css_sets() epitomizes this confusion - @[old_]cg are struct
css_set while @cg[12] are struct cgroup.
It's not like the whole deal with cgroup, css_set and cg_cgroup_link
isn't already confusing enough. Let's give it some sanity by
uniformly using @cset for all struct css_set variables.
* s/cg/cset/ for all css_set variables.
* s/oldcg/old_cset/ s/oldcgrp/old_cgrp/. The same for the ones
prefixed with "new".
* s/cg/cgrp/ for cgroup variables in compare_css_sets().
* s/css/cset/ for the cgroup variable in task_cgroup_from_root().
* Whiteline adjustments.
This patch is purely cosmetic.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
* s/percpu_ref_release/percpu_ref_func_t/ as it's customary to have _t
postfix for types and the type is gonna be used for a different type
of callback too.
* Add @ARG to function comments.
* Drop unnecessary and unaligned indentation from percpu_ref_init()
function comment.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Kent Overstreet <koverstreet@google.com>
percpu_ref_get/put() are using preempt_disable/enable() while
percpu_ref_kill() is using plain call_rcu() instead of
call_rcu_sched(). This is buggy as grace periods of the two may not
match. Fix it by using plain RCU in percpu_ref_get/put().
(I suggested using sched RCU in the first place but there's no actual
benefit in doing so unless we're gonna introduce different variants
of get/put to be called while preemption is alredy disabled, which we
definitely shouldn't.)
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Kent Overstreet <koverstreet@google.com>
* Rename it from files[] (really?) to cgroup_base_files[].
* Drop CGROUP_FILE_GENERIC_PREFIX which was defined as "cgroup." and
used inconsistently. Just use "cgroup." directly.
* Collect insane files at the end. Note that only the insane ones are
missing "cgroup." prefix.
This patch doesn't introduce any functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
The empty cgroup notification mechanism currently implemented in
cgroup is tragically outdated. Forking and execing userland process
stopped being a viable notification mechanism more than a decade ago.
We're gonna have a saner mechanism. Let's make it clear that this
abomination is going away.
Mark "notify_on_release" and "release_agent" with CFTYPE_INSANE.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Some resources controlled by cgroup aren't per-task and cgroup core
allowing threads of a single thread_group to be in different cgroups
forced memcg do explicitly find the group leader and use it. This is
gonna be nasty when transitioning to unified hierarchy and in general
we don't want and won't support granularity finer than processes.
Mark "tasks" with CFTYPE_INSANE.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: cgroups@vger.kernel.org
Cc: Vivek Goyal <vgoyal@redhat.com>
The cmpxchg() was just to ensure the debug check didn't race, which was
a bit excessive. The caller is supposed to do the appropriate
synchronization, which means percpu_ref_kill() can just do a simple
store.
Signed-off-by: Kent Overstreet <koverstreet@google.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This implements a refcount with similar semantics to
atomic_get()/atomic_dec_and_test() - but percpu.
It also implements two stage shutdown, as we need it to tear down the
percpu counts. Before dropping the initial refcount, you must call
percpu_ref_kill(); this puts the refcount in "shutting down mode" and
switches back to a single atomic refcount with the appropriate
barriers (synchronize_rcu()).
It's also legal to call percpu_ref_kill() multiple times - it only
returns true once, so callers don't have to reimplement shutdown
synchronization.
[akpm@linux-foundation.org: fix build]
[akpm@linux-foundation.org: coding-style tweak]
Signed-off-by: Kent Overstreet <koverstreet@google.com>
Cc: Zach Brown <zab@redhat.com>
Cc: Felipe Balbi <balbi@ti.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Asai Thambi S P <asamymuthupa@micron.com>
Cc: Selvan Mani <smani@micron.com>
Cc: Sam Bradshaw <sbradshaw@micron.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Reviewed-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Tejun Heo <tj@kernel.org>
Li Zefan
Tejun Heo
Kent Overstreet