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cgroup: Merge branch 'for-6.17-fixes' into for-6.18

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Pull for-6.17-fixes to receive 79f919a89c ("cgroup: split
cgroup_destroy_wq into 3 workqueues") to resolve its conflict with
7fa33aa3b0 ("cgroup: WQ_PERCPU added to alloc_workqueue users"). The
latter adds WQ_PERCPU when creating cgroup_destroy_wq and the former splits
the workqueue into three. Resolve by applying WQ_PERCPU to the three split
workqueues.

Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo 2025-09-05 07:08:26 -10:00
commit 4a3e62dfa7
2 changed files with 39 additions and 9 deletions
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4
Documentation/admin-guide/cgroup-v2.rst
View File

@ -435,8 +435,8 @@ both cgroups.
Controlling Controllers
-----------------------
Availablity
~~~~~~~~~~~
Availability
~~~~~~~~~~~~
A controller is available in a cgroup when it is supported by the kernel (i.e.,
compiled in, not disabled and not attached to a v1 hierarchy) and listed in the

44
kernel/cgroup/cgroup.c
View File

@ -126,8 +126,31 @@ DEFINE_PERCPU_RWSEM(cgroup_threadgroup_rwsem);
* of concurrent destructions. Use a separate workqueue so that cgroup
* destruction work items don't end up filling up max_active of system_percpu_wq
* which may lead to deadlock.
*
* A cgroup destruction should enqueue work sequentially to:
* cgroup_offline_wq: use for css offline work
* cgroup_release_wq: use for css release work
* cgroup_free_wq: use for free work
*
* Rationale for using separate workqueues:
* The cgroup root free work may depend on completion of other css offline
* operations. If all tasks were enqueued to a single workqueue, this could
* create a deadlock scenario where:
* - Free work waits for other css offline work to complete.
* - But other css offline work is queued after free work in the same queue.
*
* Example deadlock scenario with single workqueue (cgroup_destroy_wq):
* 1. umount net_prio
* 2. net_prio root destruction enqueues work to cgroup_destroy_wq (CPUx)
* 3. perf_event CSS A offline enqueues work to same cgroup_destroy_wq (CPUx)
* 4. net_prio cgroup_destroy_root->cgroup_lock_and_drain_offline.
* 5. net_prio root destruction blocks waiting for perf_event CSS A offline,
* which can never complete as it's behind in the same queue and
* workqueue's max_active is 1.
*/
static struct workqueue_struct *cgroup_destroy_wq;
static struct workqueue_struct *cgroup_offline_wq;
static struct workqueue_struct *cgroup_release_wq;
static struct workqueue_struct *cgroup_free_wq;
/* generate an array of cgroup subsystem pointers */
#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
@ -4173,6 +4196,7 @@ static void cgroup_file_release(struct kernfs_open_file *of)
cft->release(of);
put_cgroup_ns(ctx->ns);
kfree(ctx);
of->priv = NULL;
}
static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
@ -5577,7 +5601,7 @@ static void css_release_work_fn(struct work_struct *work)
cgroup_unlock();
INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
queue_rcu_work(cgroup_free_wq, &css->destroy_rwork);
}
static void css_release(struct percpu_ref *ref)
@ -5586,7 +5610,7 @@ static void css_release(struct percpu_ref *ref)
container_of(ref, struct cgroup_subsys_state, refcnt);
INIT_WORK(&css->destroy_work, css_release_work_fn);
queue_work(cgroup_destroy_wq, &css->destroy_work);
queue_work(cgroup_release_wq, &css->destroy_work);
}
static void init_and_link_css(struct cgroup_subsys_state *css,
@ -5720,7 +5744,7 @@ static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
list_del_rcu(&css->sibling);
err_free_css:
INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
queue_rcu_work(cgroup_free_wq, &css->destroy_rwork);
return ERR_PTR(err);
}
@ -5960,7 +5984,7 @@ static void css_killed_ref_fn(struct percpu_ref *ref)
if (atomic_dec_and_test(&css->online_cnt)) {
INIT_WORK(&css->destroy_work, css_killed_work_fn);
queue_work(cgroup_destroy_wq, &css->destroy_work);
queue_work(cgroup_offline_wq, &css->destroy_work);
}
}
@ -6346,8 +6370,14 @@ static int __init cgroup_wq_init(void)
* 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", WQ_PERCPU, 1);
BUG_ON(!cgroup_destroy_wq);
cgroup_offline_wq = alloc_workqueue("cgroup_offline", WQ_PERCPU, 1);
BUG_ON(!cgroup_offline_wq);
cgroup_release_wq = alloc_workqueue("cgroup_release", WQ_PERCPU, 1);
BUG_ON(!cgroup_release_wq);
cgroup_free_wq = alloc_workqueue("cgroup_free", WQ_PERCPU, 1);
BUG_ON(!cgroup_free_wq);
return 0;
}
core_initcall(cgroup_wq_init);