0ab66088c8
sysfs: implement sysfs_dirent active reference and immediate disconnect Opening a sysfs node references its associated kobject, so userland can arbitrarily prolong lifetime of a kobject which complicates lifetime rules in drivers. This patch implements active reference and makes the association between kobject and sysfs immediately breakable. Now each sysfs_dirent has two reference counts - s_count and s_active. s_count is a regular reference count which guarantees that the containing sysfs_dirent is accessible. As long as s_count reference is held, all sysfs internal fields in sysfs_dirent are accessible including s_parent and s_name. The newly added s_active is active reference count. This is acquired by invoking sysfs_get_active() and it's the caller's responsibility to ensure sysfs_dirent itself is accessible (should be holding s_count one way or the other). Dereferencing sysfs_dirent to access objects out of sysfs proper requires active reference. This includes access to the associated kobjects, attributes and ops. The active references can be drained and denied by calling sysfs_deactivate(). All active sysfs_dirents must be deactivated after deletion but before the default reference is dropped. This enables immediate disconnect of sysfs nodes. Once a sysfs_dirent is deleted, it won't access any entity external to sysfs proper. Because attr/bin_attr ops access both the node itself and its parent for kobject, they need to hold active references to both. sysfs_get/put_active_two() helpers are provided to help grabbing both references. Parent's is acquired first and released last. Unlike other operations, mmapped area lingers on after mmap() is finished and the module implement implementing it and kobj need to stay referenced till all the mapped pages are gone. This is accomplished by holding one set of active references to the bin_attr and its parent if there have been any mmap during lifetime of an openfile. The references are dropped when the openfile is released. This change makes sysfs lifetime rules independent from both kobject's and module's. It not only fixes several race conditions caused by sysfs not holding onto the proper module when referencing kobject, but also helps fixing and simplifying lifetime management in driver model and drivers by taking sysfs out of the equation. Please read the following message for more info. http://article.gmane.org/gmane.linux.kernel/510293 Signed-off-by: Tejun Heo <htejun@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
214 lines
5.6 KiB
C
214 lines
5.6 KiB
C
struct sysfs_elem_dir {
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struct kobject * kobj;
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};
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struct sysfs_elem_symlink {
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struct sysfs_dirent * target_sd;
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};
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struct sysfs_elem_attr {
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struct attribute * attr;
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};
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struct sysfs_elem_bin_attr {
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struct bin_attribute * bin_attr;
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};
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/*
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* As long as s_count reference is held, the sysfs_dirent itself is
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* accessible. Dereferencing s_elem or any other outer entity
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* requires s_active reference.
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*/
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struct sysfs_dirent {
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atomic_t s_count;
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struct rw_semaphore s_active;
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struct sysfs_dirent * s_parent;
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struct list_head s_sibling;
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struct list_head s_children;
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const char * s_name;
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union {
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struct sysfs_elem_dir dir;
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struct sysfs_elem_symlink symlink;
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struct sysfs_elem_attr attr;
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struct sysfs_elem_bin_attr bin_attr;
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} s_elem;
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int s_type;
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umode_t s_mode;
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ino_t s_ino;
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struct dentry * s_dentry;
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struct iattr * s_iattr;
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atomic_t s_event;
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};
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/*
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* A sysfs file which deletes another file when written to need to
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* write lock the s_active of the victim while its s_active is read
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* locked for the write operation. Tell lockdep that this is okay.
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*/
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enum sysfs_s_active_class
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{
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SYSFS_S_ACTIVE_NORMAL, /* file r/w access, etc - default */
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SYSFS_S_ACTIVE_DEACTIVATE, /* file deactivation */
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};
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extern struct vfsmount * sysfs_mount;
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extern struct kmem_cache *sysfs_dir_cachep;
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extern void sysfs_delete_inode(struct inode *inode);
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extern struct inode * sysfs_new_inode(mode_t mode, struct sysfs_dirent *);
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extern int sysfs_create(struct dentry *, int mode, int (*init)(struct inode *));
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extern void release_sysfs_dirent(struct sysfs_dirent * sd);
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extern int sysfs_dirent_exist(struct sysfs_dirent *, const unsigned char *);
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extern struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode,
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int type);
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extern void sysfs_attach_dirent(struct sysfs_dirent *sd,
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struct sysfs_dirent *parent_sd,
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struct dentry *dentry);
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extern int sysfs_add_file(struct dentry *, const struct attribute *, int);
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extern int sysfs_hash_and_remove(struct dentry * dir, const char * name);
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extern struct sysfs_dirent *sysfs_find(struct sysfs_dirent *dir, const char * name);
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extern int sysfs_create_subdir(struct kobject *, const char *, struct dentry **);
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extern void sysfs_remove_subdir(struct dentry *);
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extern void sysfs_drop_dentry(struct sysfs_dirent *sd, struct dentry *parent);
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extern int sysfs_setattr(struct dentry *dentry, struct iattr *iattr);
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extern spinlock_t sysfs_lock;
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extern spinlock_t kobj_sysfs_assoc_lock;
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extern struct rw_semaphore sysfs_rename_sem;
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extern struct super_block * sysfs_sb;
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extern const struct file_operations sysfs_dir_operations;
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extern const struct file_operations sysfs_file_operations;
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extern const struct file_operations bin_fops;
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extern const struct inode_operations sysfs_dir_inode_operations;
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extern const struct inode_operations sysfs_symlink_inode_operations;
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struct sysfs_buffer {
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struct list_head associates;
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size_t count;
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loff_t pos;
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char * page;
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struct sysfs_ops * ops;
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struct semaphore sem;
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int orphaned;
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int needs_read_fill;
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int event;
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};
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struct sysfs_buffer_collection {
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struct list_head associates;
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};
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static inline struct sysfs_dirent * sysfs_get(struct sysfs_dirent * sd)
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{
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if (sd) {
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WARN_ON(!atomic_read(&sd->s_count));
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atomic_inc(&sd->s_count);
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}
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return sd;
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}
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static inline void sysfs_put(struct sysfs_dirent * sd)
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{
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if (sd && atomic_dec_and_test(&sd->s_count))
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release_sysfs_dirent(sd);
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}
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/**
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* sysfs_get_active - get an active reference to sysfs_dirent
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* @sd: sysfs_dirent to get an active reference to
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*
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* Get an active reference of @sd. This function is noop if @sd
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* is NULL.
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*
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* RETURNS:
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* Pointer to @sd on success, NULL on failure.
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*/
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static inline struct sysfs_dirent *sysfs_get_active(struct sysfs_dirent *sd)
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{
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if (sd) {
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if (unlikely(!down_read_trylock(&sd->s_active)))
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sd = NULL;
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}
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return sd;
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}
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/**
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* sysfs_put_active - put an active reference to sysfs_dirent
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* @sd: sysfs_dirent to put an active reference to
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*
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* Put an active reference to @sd. This function is noop if @sd
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* is NULL.
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*/
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static inline void sysfs_put_active(struct sysfs_dirent *sd)
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{
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if (sd)
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up_read(&sd->s_active);
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}
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/**
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* sysfs_get_active_two - get active references to sysfs_dirent and parent
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* @sd: sysfs_dirent of interest
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*
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* Get active reference to @sd and its parent. Parent's active
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* reference is grabbed first. This function is noop if @sd is
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* NULL.
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*
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* RETURNS:
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* Pointer to @sd on success, NULL on failure.
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*/
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static inline struct sysfs_dirent *sysfs_get_active_two(struct sysfs_dirent *sd)
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{
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if (sd) {
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if (sd->s_parent && unlikely(!sysfs_get_active(sd->s_parent)))
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return NULL;
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if (unlikely(!sysfs_get_active(sd))) {
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sysfs_put_active(sd->s_parent);
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return NULL;
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}
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}
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return sd;
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}
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/**
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* sysfs_put_active_two - put active references to sysfs_dirent and parent
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* @sd: sysfs_dirent of interest
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*
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* Put active references to @sd and its parent. This function is
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* noop if @sd is NULL.
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*/
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static inline void sysfs_put_active_two(struct sysfs_dirent *sd)
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{
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if (sd) {
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sysfs_put_active(sd);
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sysfs_put_active(sd->s_parent);
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}
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}
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/**
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* sysfs_deactivate - deactivate sysfs_dirent
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* @sd: sysfs_dirent to deactivate
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*
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* Deny new active references and drain existing ones. s_active
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* will be unlocked when the sysfs_dirent is released.
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*/
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static inline void sysfs_deactivate(struct sysfs_dirent *sd)
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{
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down_write_nested(&sd->s_active, SYSFS_S_ACTIVE_DEACTIVATE);
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/* s_active will be unlocked by the thread doing the final put
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* on @sd. Lie to lockdep.
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*/
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rwsem_release(&sd->s_active.dep_map, 1, _RET_IP_);
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}
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static inline int sysfs_is_shadowed_inode(struct inode *inode)
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{
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return S_ISDIR(inode->i_mode) && inode->i_op->follow_link;
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}
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