diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/cgroup.c | 58 | ||||
| -rw-r--r-- | kernel/cpuset.c | 20 |
2 files changed, 69 insertions, 9 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 7868fc3c0bc5..70776aec2562 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -1648,10 +1648,13 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, int flags, const char *unused_dev_name, void *data) { + struct super_block *pinned_sb = NULL; + struct cgroup_subsys *ss; struct cgroup_root *root; struct cgroup_sb_opts opts; struct dentry *dentry; int ret; + int i; bool new_sb; /* @@ -1677,6 +1680,27 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, goto out_unlock; } + /* + * Destruction of cgroup root is asynchronous, so subsystems may + * still be dying after the previous unmount. Let's drain the + * dying subsystems. We just need to ensure that the ones + * unmounted previously finish dying and don't care about new ones + * starting. Testing ref liveliness is good enough. + */ + for_each_subsys(ss, i) { + if (!(opts.subsys_mask & (1 << i)) || + ss->root == &cgrp_dfl_root) + continue; + + if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt)) { + mutex_unlock(&cgroup_mutex); + msleep(10); + ret = restart_syscall(); + goto out_free; + } + cgroup_put(&ss->root->cgrp); + } + for_each_root(root) { bool name_match = false; @@ -1717,15 +1741,23 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, } /* - * A root's lifetime is governed by its root cgroup. - * tryget_live failure indicate that the root is being - * destroyed. Wait for destruction to complete so that the - * subsystems are free. We can use wait_queue for the wait - * but this path is super cold. Let's just sleep for a bit - * and retry. + * We want to reuse @root whose lifetime is governed by its + * ->cgrp. Let's check whether @root is alive and keep it + * that way. As cgroup_kill_sb() can happen anytime, we + * want to block it by pinning the sb so that @root doesn't + * get killed before mount is complete. + * + * With the sb pinned, tryget_live can reliably indicate + * whether @root can be reused. If it's being killed, + * drain it. We can use wait_queue for the wait but this + * path is super cold. Let's just sleep a bit and retry. */ - if (!percpu_ref_tryget_live(&root->cgrp.self.refcnt)) { + pinned_sb = kernfs_pin_sb(root->kf_root, NULL); + if (IS_ERR(pinned_sb) || + !percpu_ref_tryget_live(&root->cgrp.self.refcnt)) { mutex_unlock(&cgroup_mutex); + if (!IS_ERR_OR_NULL(pinned_sb)) + deactivate_super(pinned_sb); msleep(10); ret = restart_syscall(); goto out_free; @@ -1770,6 +1802,16 @@ out_free: CGROUP_SUPER_MAGIC, &new_sb); if (IS_ERR(dentry) || !new_sb) cgroup_put(&root->cgrp); + + /* + * If @pinned_sb, we're reusing an existing root and holding an + * extra ref on its sb. Mount is complete. Put the extra ref. + */ + if (pinned_sb) { + WARN_ON(new_sb); + deactivate_super(pinned_sb); + } + return dentry; } @@ -3328,7 +3370,7 @@ bool css_has_online_children(struct cgroup_subsys_state *css) rcu_read_lock(); css_for_each_child(child, css) { - if (css->flags & CSS_ONLINE) { + if (child->flags & CSS_ONLINE) { ret = true; break; } diff --git a/kernel/cpuset.c b/kernel/cpuset.c index f6b33c696224..116a4164720a 100644 --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -1181,7 +1181,13 @@ done: int current_cpuset_is_being_rebound(void) { - return task_cs(current) == cpuset_being_rebound; + int ret; + + rcu_read_lock(); + ret = task_cs(current) == cpuset_being_rebound; + rcu_read_unlock(); + + return ret; } static int update_relax_domain_level(struct cpuset *cs, s64 val) @@ -1617,7 +1623,17 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of, * resources, wait for the previously scheduled operations before * proceeding, so that we don't end up keep removing tasks added * after execution capability is restored. + * + * cpuset_hotplug_work calls back into cgroup core via + * cgroup_transfer_tasks() and waiting for it from a cgroupfs + * operation like this one can lead to a deadlock through kernfs + * active_ref protection. Let's break the protection. Losing the + * protection is okay as we check whether @cs is online after + * grabbing cpuset_mutex anyway. This only happens on the legacy + * hierarchies. */ + css_get(&cs->css); + kernfs_break_active_protection(of->kn); flush_work(&cpuset_hotplug_work); mutex_lock(&cpuset_mutex); @@ -1645,6 +1661,8 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of, free_trial_cpuset(trialcs); out_unlock: mutex_unlock(&cpuset_mutex); + kernfs_unbreak_active_protection(of->kn); + css_put(&cs->css); return retval ?: nbytes; } |