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cgroup: update locking in cgroup_show_options()
cgroup_show_options() grabs cgroup_root_mutex to protect the options changing while printing; however, holding root_mutex or not doesn't really make much difference for the function. subsys_mask can be atomically tested and most of the options aren't allowed to change anyway once mounted. The only field which needs synchronization is ->release_agent_path. This patch introduces a dedicated spinlock to synchronize accesses to the field and drops cgroup_root_mutex locking from cgroup_show_options(). The next patch will remove cgroup_root_mutex. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
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parent
aec25020f5
commit
69e943b7d3
1 changed files with 16 additions and 3 deletions
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@ -92,6 +92,12 @@ static DEFINE_MUTEX(cgroup_mutex);
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static DEFINE_MUTEX(cgroup_root_mutex);
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/*
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* Protects cgroup_subsys->release_agent_path. Modifying it also requires
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* cgroup_mutex. Reading requires either cgroup_mutex or this spinlock.
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*/
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static DEFINE_SPINLOCK(release_agent_path_lock);
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#define cgroup_assert_mutex_or_rcu_locked() \
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rcu_lockdep_assert(rcu_read_lock_held() || \
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lockdep_is_held(&cgroup_mutex), \
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@ -1034,7 +1040,6 @@ static int cgroup_show_options(struct seq_file *seq, struct dentry *dentry)
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struct cgroup_subsys *ss;
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int ssid;
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mutex_lock(&cgroup_root_mutex);
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for_each_subsys(ss, ssid)
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if (root->subsys_mask & (1 << ssid))
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seq_printf(seq, ",%s", ss->name);
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@ -1044,13 +1049,16 @@ static int cgroup_show_options(struct seq_file *seq, struct dentry *dentry)
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seq_puts(seq, ",noprefix");
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if (root->flags & CGRP_ROOT_XATTR)
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seq_puts(seq, ",xattr");
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spin_lock(&release_agent_path_lock);
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if (strlen(root->release_agent_path))
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seq_printf(seq, ",release_agent=%s", root->release_agent_path);
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spin_unlock(&release_agent_path_lock);
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if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->top_cgroup.flags))
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seq_puts(seq, ",clone_children");
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if (strlen(root->name))
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seq_printf(seq, ",name=%s", root->name);
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mutex_unlock(&cgroup_root_mutex);
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return 0;
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}
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@ -1272,8 +1280,11 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
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if (ret)
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goto out_unlock;
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if (opts.release_agent)
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if (opts.release_agent) {
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spin_lock(&release_agent_path_lock);
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strcpy(root->release_agent_path, opts.release_agent);
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spin_unlock(&release_agent_path_lock);
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}
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out_unlock:
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kfree(opts.release_agent);
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kfree(opts.name);
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@ -2183,7 +2194,9 @@ static int cgroup_release_agent_write(struct cgroup_subsys_state *css,
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if (!cgroup_lock_live_group(css->cgroup))
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return -ENODEV;
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mutex_lock(&cgroup_root_mutex);
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spin_lock(&release_agent_path_lock);
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strcpy(css->cgroup->root->release_agent_path, buffer);
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spin_unlock(&release_agent_path_lock);
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mutex_unlock(&cgroup_root_mutex);
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mutex_unlock(&cgroup_mutex);
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return 0;
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