diff options
| author | Tejun Heo <tj@kernel.org> | 2013-08-15 11:42:36 -0400 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2013-08-19 09:56:25 -0400 |
| commit | 0bfb4aa67cef4982adc70590a31624d7b35a0bda (patch) | |
| tree | 89a20d8b76a803e2ac6e04c032b97e35f392fd8f /kernel/cgroup.c | |
| parent | 1cb650b91ba582f6737457b7d22e368585596d2c (diff) | |
cgroup: fix subsystem file accesses on the root cgroup
105347ba5 ("cgroup: make cgroup_file_open() rcu_read_lock() around
cgroup_css() and add cfent->css") added cfent->css to cache the
associted cgroup_subsys_state across file operations.
A cfent is associated with single css throughout its lifetime and the
origimal commit initialized the cache pointer during cgroup_add_file()
and verified that it matches the actual one in cgroup_file_open().
While this works fine for !root cgroups, it's broken for root cgroups
as files in a root cgroup are created before the css's are associated
with the cgroup and thus cgroup_css() call in cgroup_add_file()
returns NULL associating all cfents in the root cgroup with NULL css.
This makes cgroup_file_open() trigger WARN and fail with -ENODEV for
all !core subsystem files in the root cgroups.
There's no reason to initialize cfent->css separately from
cgroup_add_file(). As the association never changes,
cgroup_file_open() can set it unconditionally every time and
containing the logic in cgroup_file_open() makes more sense anyway as
the only reason it's necessary is file->private_data being already
occupied.
Fix it by setting cfent->css unconditionally from cgroup_file_open().
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Diffstat (limited to 'kernel/cgroup.c')
| -rw-r--r-- | kernel/cgroup.c | 24 |
1 files changed, 10 insertions, 14 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index ff7d642a070..896e035eb6e 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2490,10 +2490,18 @@ static int cgroup_file_open(struct inode *inode, struct file *file) } rcu_read_unlock(); - /* css should match @cfe->css, see cgroup_add_file() for details */ - if (!css || WARN_ON_ONCE(css != cfe->css)) + if (!css) return -ENODEV; + /* + * @cfe->css is used by read/write/close to determine the + * associated css. @file->private_data would be a better place but + * that's already used by seqfile. Multiple accessors may use it + * simultaneously which is okay as the association never changes. + */ + WARN_ON_ONCE(cfe->css && cfe->css != css); + cfe->css = css; + if (cft->read_map || cft->read_seq_string) { file->f_op = &cgroup_seqfile_operations; err = single_open(file, cgroup_seqfile_show, cfe); @@ -2772,18 +2780,6 @@ static int cgroup_add_file(struct cgroup *cgrp, struct cftype *cft) dentry->d_fsdata = cfe; simple_xattrs_init(&cfe->xattrs); - /* - * cfe->css is used by read/write/close to determine the associated - * css. file->private_data would be a better place but that's - * already used by seqfile. Note that open will use the usual - * cgroup_css() and css_tryget() to acquire the css and this - * caching doesn't affect css lifetime management. - */ - if (cft->ss) - cfe->css = cgroup_css(cgrp, cft->ss->subsys_id); - else - cfe->css = &cgrp->dummy_css; - mode = cgroup_file_mode(cft); error = cgroup_create_file(dentry, mode | S_IFREG, cgrp->root->sb); if (!error) { |