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author | Tejun Heo <tj@kernel.org> | 2013-11-22 17:14:39 -0500 |
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committer | Tejun Heo <tj@kernel.org> | 2013-11-22 17:14:39 -0500 |
commit | e5fca243abae1445afbfceebda5f08462ef869d3 (patch) | |
tree | 4c5dc3301b6fe77fc70b4567c9f2c89c42a8d34c /kernel/cgroup.c | |
parent | 6ce4eac1f600b34f2f7f58f9cd8f0503d79e42ae (diff) | |
download | op-kernel-dev-e5fca243abae1445afbfceebda5f08462ef869d3.zip op-kernel-dev-e5fca243abae1445afbfceebda5f08462ef869d3.tar.gz |
cgroup: use a dedicated workqueue for cgroup destruction
Since be44562613851 ("cgroup: remove synchronize_rcu() from
cgroup_diput()"), cgroup destruction path makes use of workqueue. css
freeing is performed from a work item from that point on and a later
commit, ea15f8ccdb430 ("cgroup: split cgroup destruction into two
steps"), moves css offlining to workqueue too.
As cgroup destruction isn't depended upon for memory reclaim, the
destruction work items were put on the system_wq; unfortunately, some
controller may block in the destruction path for considerable duration
while holding cgroup_mutex. As large part of destruction path is
synchronized through cgroup_mutex, when combined with high rate of
cgroup removals, this has potential to fill up system_wq's max_active
of 256.
Also, it turns out that memcg's css destruction path ends up queueing
and waiting for work items on system_wq through work_on_cpu(). If
such operation happens while system_wq is fully occupied by cgroup
destruction work items, work_on_cpu() can't make forward progress
because system_wq is full and other destruction work items on
system_wq can't make forward progress because the work item waiting
for work_on_cpu() is holding cgroup_mutex, leading to deadlock.
This can be fixed by queueing destruction work items on a separate
workqueue. This patch creates a dedicated workqueue -
cgroup_destroy_wq - for this purpose. As these work items shouldn't
have inter-dependencies and mostly serialized by cgroup_mutex anyway,
giving high concurrency level doesn't buy anything and the workqueue's
@max_active is set to 1 so that destruction work items are executed
one by one on each CPU.
Hugh Dickins: Because cgroup_init() is run before init_workqueues(),
cgroup_destroy_wq can't be allocated from cgroup_init(). Do it from a
separate core_initcall(). In the future, we probably want to reorder
so that workqueue init happens before cgroup_init().
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Hugh Dickins <hughd@google.com>
Reported-by: Shawn Bohrer <shawn.bohrer@gmail.com>
Link: http://lkml.kernel.org/r/20131111220626.GA7509@sbohrermbp13-local.rgmadvisors.com
Link: http://lkml.kernel.org/g/alpine.LNX.2.00.1310301606080.2333@eggly.anvils
Cc: stable@vger.kernel.org # v3.9+
Diffstat (limited to 'kernel/cgroup.c')
-rw-r--r-- | kernel/cgroup.c | 30 |
1 files changed, 27 insertions, 3 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 4c62513..a7b98ee 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -90,6 +90,14 @@ static DEFINE_MUTEX(cgroup_mutex); static DEFINE_MUTEX(cgroup_root_mutex); /* + * cgroup destruction makes heavy use of work items and there can be a lot + * of concurrent destructions. Use a separate workqueue so that cgroup + * destruction work items don't end up filling up max_active of system_wq + * which may lead to deadlock. + */ +static struct workqueue_struct *cgroup_destroy_wq; + +/* * Generate an array of cgroup subsystem pointers. At boot time, this is * populated with the built in subsystems, and modular subsystems are * registered after that. The mutable section of this array is protected by @@ -871,7 +879,7 @@ static void cgroup_free_rcu(struct rcu_head *head) struct cgroup *cgrp = container_of(head, struct cgroup, rcu_head); INIT_WORK(&cgrp->destroy_work, cgroup_free_fn); - schedule_work(&cgrp->destroy_work); + queue_work(cgroup_destroy_wq, &cgrp->destroy_work); } static void cgroup_diput(struct dentry *dentry, struct inode *inode) @@ -4249,7 +4257,7 @@ static void css_free_rcu_fn(struct rcu_head *rcu_head) * css_put(). dput() requires process context which we don't have. */ INIT_WORK(&css->destroy_work, css_free_work_fn); - schedule_work(&css->destroy_work); + queue_work(cgroup_destroy_wq, &css->destroy_work); } static void css_release(struct percpu_ref *ref) @@ -4539,7 +4547,7 @@ static void css_killed_ref_fn(struct percpu_ref *ref) container_of(ref, struct cgroup_subsys_state, refcnt); INIT_WORK(&css->destroy_work, css_killed_work_fn); - schedule_work(&css->destroy_work); + queue_work(cgroup_destroy_wq, &css->destroy_work); } /** @@ -5063,6 +5071,22 @@ out: return err; } +static int __init cgroup_wq_init(void) +{ + /* + * There isn't much point in executing destruction path in + * parallel. Good chunk is serialized with cgroup_mutex anyway. + * Use 1 for @max_active. + * + * We would prefer to do this in cgroup_init() above, but that + * is called before init_workqueues(): so leave this until after. + */ + cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1); + BUG_ON(!cgroup_destroy_wq); + return 0; +} +core_initcall(cgroup_wq_init); + /* * proc_cgroup_show() * - Print task's cgroup paths into seq_file, one line for each hierarchy |