Re: [PATCH] devcgroup: avoid using cgroup_lock

Serge E. Hallyn
2009-03-12T18:19:26Z

Quoting Li Zefan (lizf@cn.fujitsu.com):
> There is nothing special that has to be protected by cgroup_lock,
> so introduce devcgroup_mtuex for it's own use.
>
> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
> ---
> security/device_cgroup.c | 21 +++++++++++++--------
> 1 files changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/security/device_cgroup.c b/security/device_cgroup.c
> index 3aacd0f..5fda7df 100644
> --- a/security/device_cgroup.c
> +++ b/security/device_cgroup.c
> @@ -11,6 +11,7 @@
> #include <linux/uaccess.h>
> #include <linux/seq_file.h>
> #include <linux/rcupdate.h>
> +#include <linux/mutex.h>
>
> #define ACC_MKNOD 1
> #define ACC_READ 2
> @@ -21,9 +22,11 @@
> #define DEV_CHAR 2
> #define DEV_ALL 4 /* this represents all devices */
>
> +static DEFINE_MUTEX(devcgroup_mutex);
> +
> /*
> * whitelist locking rules:
> - * hold cgroup_lock() for update/read.
> + * hold devcgroup_mutex for update/read.
> * hold rcu_read_lock() for read.
> */
>
> @@ -67,7 +70,7 @@ static int devcgroup_can_attach(struct cgroup_subsys *ss,
> }
>
> /*
> - * called under cgroup_lock()
> + * called under devcgroup_mutex
> */
> static int dev_whitelist_copy(struct list_head *dest, struct list_head *orig)
> {
> @@ -92,7 +95,7 @@ free_and_exit:
>
> /* Stupid prototype - don't bother combining existing entries */
> /*
> - * called under cgroup_lock()
> + * called under devcgroup_mutex
> */
> static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
> struct dev_whitelist_item *wh)
> @@ -130,7 +133,7 @@ static void whitelist_item_free(struct rcu_head *rcu)
> }
>
> /*
> - * called under cgroup_lock()
> + * called under devcgroup_mutex
> */
> static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup,
> struct dev_whitelist_item *wh)
> @@ -185,8 +188,10 @@ static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss,
> list_add(&wh->list, &dev_cgroup->whitelist);
> } else {
> parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
> + mutex_lock(&devcgroup_mutex);
> ret = dev_whitelist_copy(&dev_cgroup->whitelist,
> &parent_dev_cgroup->whitelist);
> + mutex_unlock(&devcgroup_mutex);
> if (ret) {
> kfree(dev_cgroup);
> return ERR_PTR(ret);
> @@ -273,7 +278,7 @@ static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
> * does the access granted to dev_cgroup c contain the access
> * requested in whitelist item refwh.
> * return 1 if yes, 0 if no.
> - * call with c->lock held
> + * call with devcgroup_mutex held
> */
> static int may_access_whitelist(struct dev_cgroup *c,
> struct dev_whitelist_item *refwh)
> @@ -426,11 +431,11 @@ static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
> const char *buffer)
> {
> int retval;
> - if (!cgroup_lock_live_group(cgrp))

Does it matter that we no longer check for cgroup_is_removed()?

> - return -ENODEV;
> +
> + mutex_lock(&devcgroup_mutex);
> retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
> cft->private, buffer);
> - cgroup_unlock();
> + mutex_unlock(&devcgroup_mutex);
> return retval;
> }
>
> --
> 1.5.4.rc3