| From | Greg Kroah-Hartman <> | Subject | [PATCH 3.15 70/84] kernfs: introduce kernfs_pin_sb() | Date | Tue, 15 Jul 2014 16:18:07 -0700 |
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3.15-stable review patch. If anyone has any objections, please let me know.
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From: Li Zefan <lizefan@huawei.com>
commit 4e26445faad366d67d7723622bf6a60a6f0f5993 upstream.
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. ] Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Li Zefan <lizefan@huawei.com> Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- fs/kernfs/mount.c | 30 ++++++++++++++++++++++++++++++ include/linux/kernfs.h | 1 + 2 files changed, 31 insertions(+)
--- a/fs/kernfs/mount.c +++ b/fs/kernfs/mount.c @@ -211,6 +211,36 @@ void kernfs_kill_sb(struct super_block * 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", --- a/include/linux/kernfs.h +++ b/include/linux/kernfs.h @@ -304,6 +304,7 @@ struct dentry *kernfs_mount_ns(struct fi struct kernfs_root *root, unsigned long magic, bool *new_sb_created, const void *ns); void kernfs_kill_sb(struct super_block *sb); +struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns); void kernfs_init(void);
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