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author | Li Zefan <lizefan@huawei.com> | 2014-06-30 05:50:28 +0200 |
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committer | Tejun Heo <tj@kernel.org> | 2014-06-30 16:16:25 +0200 |
commit | 4e26445faad366d67d7723622bf6a60a6f0f5993 (patch) | |
tree | c3e0f68527e2b094af5792e31e6ec0396d784308 /fs | |
parent | cgroup: fix mount failure in a corner case (diff) | |
download | linux-4e26445faad366d67d7723622bf6a60a6f0f5993.tar.xz linux-4e26445faad366d67d7723622bf6a60a6f0f5993.zip |
kernfs: introduce kernfs_pin_sb()
kernfs_pin_sb() tries to get a refcnt of the superblock.
This will be used by cgroupfs.
v2:
- make kernfs_pin_sb() return the superblock.
- drop kernfs_drop_sb().
tj: Updated the comment a bit.
[ This is a prerequisite for a bugfix. ]
Cc: <stable@vger.kernel.org> # 3.15
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'fs')
-rw-r--r-- | fs/kernfs/mount.c | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c index d171b98a6cdd..f973ae9b05f1 100644 --- a/fs/kernfs/mount.c +++ b/fs/kernfs/mount.c @@ -211,6 +211,36 @@ void kernfs_kill_sb(struct super_block *sb) kernfs_put(root_kn); } +/** + * kernfs_pin_sb: try to pin the superblock associated with a kernfs_root + * @kernfs_root: the kernfs_root in question + * @ns: the namespace tag + * + * Pin the superblock so the superblock won't be destroyed in subsequent + * operations. This can be used to block ->kill_sb() which may be useful + * for kernfs users which dynamically manage superblocks. + * + * Returns NULL if there's no superblock associated to this kernfs_root, or + * -EINVAL if the superblock is being freed. + */ +struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns) +{ + struct kernfs_super_info *info; + struct super_block *sb = NULL; + + mutex_lock(&kernfs_mutex); + list_for_each_entry(info, &root->supers, node) { + if (info->ns == ns) { + sb = info->sb; + if (!atomic_inc_not_zero(&info->sb->s_active)) + sb = ERR_PTR(-EINVAL); + break; + } + } + mutex_unlock(&kernfs_mutex); + return sb; +} + void __init kernfs_init(void) { kernfs_node_cache = kmem_cache_create("kernfs_node_cache", |