From 69e943b7d3c2dcca1087e03e556ac6cb0d4433b4 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Sat, 8 Feb 2014 10:36:58 -0500 Subject: [PATCH] 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 Acked-by: Li Zefan --- kernel/cgroup.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 5a77ca0784a6..b15058602120 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -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; -- 2.20.1