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authorLi Zefan <lizefan@huawei.com>2014-06-30 07:50:28 +0400
committerTejun Heo <tj@kernel.org>2014-06-30 18:16:25 +0400
commit4e26445faad366d67d7723622bf6a60a6f0f5993 (patch)
treec3e0f68527e2b094af5792e31e6ec0396d784308
parent970317aa48c6ef66cd023c039c2650c897bad927 (diff)
downloadlinux-4e26445faad366d67d7723622bf6a60a6f0f5993.tar.xz
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>
-rw-r--r--fs/kernfs/mount.c30
-rw-r--r--include/linux/kernfs.h1
2 files changed, 31 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",
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 17aa1cce6f8e..20f493564917 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -304,6 +304,7 @@ struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
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);