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cgroup: update locking in cgroup_show_options()

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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>
This commit is contained in:
Tejun Heo 2014-02-08 10:36:58 -05:00
parent aec25020f5
commit 69e943b7d3
1 changed files with 16 additions and 3 deletions
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19
kernel/cgroup.c
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@ -92,6 +92,12 @@ static DEFINE_MUTEX(cgroup_mutex);
static DEFINE_MUTEX(cgroup_root_mutex);
/*
* Protects cgroup_subsys->release_agent_path. Modifying it also requires
* cgroup_mutex. Reading requires either cgroup_mutex or this spinlock.
*/
static DEFINE_SPINLOCK(release_agent_path_lock);
#define cgroup_assert_mutex_or_rcu_locked() \
rcu_lockdep_assert(rcu_read_lock_held() || \
lockdep_is_held(&cgroup_mutex), \
@ -1034,7 +1040,6 @@ static int cgroup_show_options(struct seq_file *seq, struct dentry *dentry)
struct cgroup_subsys *ss;
int ssid;
mutex_lock(&cgroup_root_mutex);
for_each_subsys(ss, ssid)
if (root->subsys_mask & (1 << ssid))
seq_printf(seq, ",%s", ss->name);
@ -1044,13 +1049,16 @@ static int cgroup_show_options(struct seq_file *seq, struct dentry *dentry)
seq_puts(seq, ",noprefix");
if (root->flags & CGRP_ROOT_XATTR)
seq_puts(seq, ",xattr");
spin_lock(&release_agent_path_lock);
if (strlen(root->release_agent_path))
seq_printf(seq, ",release_agent=%s", root->release_agent_path);
spin_unlock(&release_agent_path_lock);
if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->top_cgroup.flags))
seq_puts(seq, ",clone_children");
if (strlen(root->name))
seq_printf(seq, ",name=%s", root->name);
mutex_unlock(&cgroup_root_mutex);
return 0;
}
@ -1272,8 +1280,11 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
if (ret)
goto out_unlock;
if (opts.release_agent)
if (opts.release_agent) {
spin_lock(&release_agent_path_lock);
strcpy(root->release_agent_path, opts.release_agent);
spin_unlock(&release_agent_path_lock);
}
out_unlock:
kfree(opts.release_agent);
kfree(opts.name);
@ -2183,7 +2194,9 @@ static int cgroup_release_agent_write(struct cgroup_subsys_state *css,
if (!cgroup_lock_live_group(css->cgroup))
return -ENODEV;
mutex_lock(&cgroup_root_mutex);
spin_lock(&release_agent_path_lock);
strcpy(css->cgroup->root->release_agent_path, buffer);
spin_unlock(&release_agent_path_lock);
mutex_unlock(&cgroup_root_mutex);
mutex_unlock(&cgroup_mutex);
return 0;