sysfs: use sysfs_mutex to protect the sysfs_dirent tree

As kobj sysfs dentries and inodes are gonna be made reclaimable,
i_mutex can't be used to protect sysfs_dirent tree.  Use sysfs_mutex
globally instead.  As the whole tree is protected with sysfs_mutex,
there is no reason to keep sysfs_rename_sem.  Drop it.

While at it, add docbook comments to functions which require
sysfs_mutex locking.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 71 insertions, 30 deletions

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 1b5643407a95..9fc8558fd86c 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -14,7 +14,7 @@
 #include <asm/semaphore.h>
 #include "sysfs.h"
 
-DECLARE_RWSEM(sysfs_rename_sem);
+DEFINE_MUTEX(sysfs_mutex);
 spinlock_t sysfs_assoc_lock = SPIN_LOCK_UNLOCKED;
 
 static spinlock_t sysfs_ino_lock = SPIN_LOCK_UNLOCKED;
@@ -28,7 +28,7 @@ static DEFINE_IDA(sysfs_ino_ida);
  *      sd->s_parent->s_children.
  *
  *      Locking:
- *      mutex_lock(sd->s_parent->dentry->d_inode->i_mutex)
+ *      mutex_lock(sysfs_mutex)
  */
 static void sysfs_link_sibling(struct sysfs_dirent *sd)
 {
@@ -47,7 +47,7 @@ static void sysfs_link_sibling(struct sysfs_dirent *sd)
  *      sd->s_parent->s_children.
  *
  *      Locking:
- *      mutex_lock(sd->s_parent->dentry->d_inode->i_mutex)
+ *      mutex_lock(sysfs_mutex)
  */
 static void sysfs_unlink_sibling(struct sysfs_dirent *sd)
 {
@@ -215,6 +215,9 @@ void release_sysfs_dirent(struct sysfs_dirent * sd)
         struct sysfs_dirent *parent_sd;
 
  repeat:
+        /* Moving/renaming is always done while holding reference.
+         * sd->s_parent won't change beneath us.
+         */
         parent_sd = sd->s_parent;
 
         if (sysfs_type(sd) == SYSFS_KOBJ_LINK)
@@ -291,6 +294,17 @@ struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode, int type)
         return NULL;
 }
 
+/**
+ *      sysfs_attach_dentry - associate sysfs_dirent with dentry
+ *      @sd: target sysfs_dirent
+ *      @dentry: dentry to associate
+ *
+ *      Associate @sd with @dentry.  This is protected by
+ *      sysfs_assoc_lock to avoid race with sysfs_d_iput().
+ *
+ *      LOCKING:
+ *      mutex_lock(sysfs_mutex)
+ */
 static void sysfs_attach_dentry(struct sysfs_dirent *sd, struct dentry *dentry)
 {
         dentry->d_op = &sysfs_dentry_ops;
@@ -304,6 +318,17 @@ static void sysfs_attach_dentry(struct sysfs_dirent *sd, struct dentry *dentry)
         d_rehash(dentry);
 }
 
+/**
+ *      sysfs_attach_dirent - attach sysfs_dirent to its parent and dentry
+ *      @sd: sysfs_dirent to attach
+ *      @parent_sd: parent to attach to (optional)
+ *      @dentry: dentry to be associated to @sd (optional)
+ *
+ *      Attach @sd to @parent_sd and/or @dentry.  Both are optional.
+ *
+ *      LOCKING:
+ *      mutex_lock(sysfs_mutex)
+ */
 void sysfs_attach_dirent(struct sysfs_dirent *sd,
                          struct sysfs_dirent *parent_sd, struct dentry *dentry)
 {
@@ -324,7 +349,7 @@ void sysfs_attach_dirent(struct sysfs_dirent *sd,
  *      Look for sysfs_dirent with name @name under @parent_sd.
  *
  *      LOCKING:
- *      mutex_lock(parent->i_mutex)
+ *      mutex_lock(sysfs_mutex)
  *
  *      RETURNS:
  *      Pointer to sysfs_dirent if found, NULL if not.
@@ -349,7 +374,7 @@ struct sysfs_dirent *sysfs_find_dirent(struct sysfs_dirent *parent_sd,
  *      it if found.
  *
  *      LOCKING:
- *      Kernel thread context (may sleep)
+ *      Kernel thread context (may sleep).  Grabs sysfs_mutex.
  *
  *      RETURNS:
  *      Pointer to sysfs_dirent if found, NULL if not.
@@ -359,10 +384,10 @@ struct sysfs_dirent *sysfs_get_dirent(struct sysfs_dirent *parent_sd,
 {
         struct sysfs_dirent *sd;
 
-        mutex_lock(&parent_sd->s_dentry->d_inode->i_mutex);
+        mutex_lock(&sysfs_mutex);
         sd = sysfs_find_dirent(parent_sd, name);
         sysfs_get(sd);
-        mutex_unlock(&parent_sd->s_dentry->d_inode->i_mutex);
+        mutex_unlock(&sysfs_mutex);
 
         return sd;
 }
@@ -408,14 +433,20 @@ static int create_dir(struct kobject *kobj, struct sysfs_dirent *parent_sd,
         }
 
         /* link in */
+        mutex_lock(&sysfs_mutex);
+
         error = -EEXIST;
-        if (sysfs_find_dirent(parent_sd, name))
+        if (sysfs_find_dirent(parent_sd, name)) {
+                mutex_unlock(&sysfs_mutex);
                 goto out_iput;
+        }
 
         sysfs_instantiate(dentry, inode);
         inc_nlink(parent->d_inode);
         sysfs_attach_dirent(sd, parent_sd, dentry);
 
+        mutex_unlock(&sysfs_mutex);
+
         *p_sd = sd;
         error = 0;
         goto out_unlock;        /* pin directory dentry in core */
@@ -493,6 +524,8 @@ static struct dentry * sysfs_lookup(struct inode *dir, struct dentry *dentry,
         if (!inode)
                 return ERR_PTR(-ENOMEM);
 
+        mutex_lock(&sysfs_mutex);
+
         if (inode->i_state & I_NEW) {
                 /* initialize inode according to type */
                 switch (sysfs_type(sd)) {
@@ -516,6 +549,8 @@ static struct dentry * sysfs_lookup(struct inode *dir, struct dentry *dentry,
         sysfs_instantiate(dentry, inode);
         sysfs_attach_dentry(sd, dentry);
 
+        mutex_unlock(&sysfs_mutex);
+
         return NULL;
 }
 
@@ -526,17 +561,13 @@ const struct inode_operations sysfs_dir_inode_operations = {
 
 static void remove_dir(struct sysfs_dirent *sd)
 {
-        struct dentry *parent = sd->s_parent->s_dentry;
-
-        mutex_lock(&parent->d_inode->i_mutex);
-
+        mutex_lock(&sysfs_mutex);
         sysfs_unlink_sibling(sd);
         sd->s_flags |= SYSFS_FLAG_REMOVED;
+        mutex_unlock(&sysfs_mutex);
 
         pr_debug(" o %s removing done\n", sd->s_name);
 
-        mutex_unlock(&parent->d_inode->i_mutex);
-
         sysfs_drop_dentry(sd);
         sysfs_deactivate(sd);
         sysfs_put(sd);
@@ -552,15 +583,12 @@ static void __sysfs_remove_dir(struct sysfs_dirent *dir_sd)
 {
         struct sysfs_dirent *removed = NULL;
         struct sysfs_dirent **pos;
-        struct dentry *dir;
 
         if (!dir_sd)
                 return;
 
-        dir = dir_sd->s_dentry;
-
         pr_debug("sysfs %s: removing dir\n", dir_sd->s_name);
-        mutex_lock(&dir->d_inode->i_mutex);
+        mutex_lock(&sysfs_mutex);
         pos = &dir_sd->s_children;
         while (*pos) {
                 struct sysfs_dirent *sd = *pos;
@@ -573,7 +601,7 @@ static void __sysfs_remove_dir(struct sysfs_dirent *dir_sd)
                 } else
                         pos = &(*pos)->s_sibling;
         }
-        mutex_unlock(&dir->d_inode->i_mutex);
+        mutex_unlock(&sysfs_mutex);
 
         while (removed) {
                 struct sysfs_dirent *sd = removed;
@@ -621,7 +649,6 @@ int sysfs_rename_dir(struct kobject *kobj, struct sysfs_dirent *new_parent_sd,
         if (!new_parent_sd)
                 return -EFAULT;
 
-        down_write(&sysfs_rename_sem);
         mutex_lock(&new_parent->d_inode->i_mutex);
 
         new_dentry = lookup_one_len(new_name, new_parent, strlen(new_name));
@@ -661,12 +688,16 @@ int sysfs_rename_dir(struct kobject *kobj, struct sysfs_dirent *new_parent_sd,
         d_add(new_dentry, NULL);
         d_move(sd->s_dentry, new_dentry);
 
+        mutex_lock(&sysfs_mutex);
+
         sysfs_unlink_sibling(sd);
         sysfs_get(new_parent_sd);
         sysfs_put(sd->s_parent);
         sd->s_parent = new_parent_sd;
         sysfs_link_sibling(sd);
 
+        mutex_unlock(&sysfs_mutex);
+
         error = 0;
         goto out_unlock;
 
@@ -678,7 +709,6 @@ int sysfs_rename_dir(struct kobject *kobj, struct sysfs_dirent *new_parent_sd,
         dput(new_dentry);
  out_unlock:
         mutex_unlock(&new_parent->d_inode->i_mutex);
-        up_write(&sysfs_rename_sem);
         return error;
 }
 
@@ -717,12 +747,15 @@ again:
         dput(new_dentry);
 
         /* Remove from old parent's list and insert into new parent's list. */
+        mutex_lock(&sysfs_mutex);
+
         sysfs_unlink_sibling(sd);
         sysfs_get(new_parent_sd);
         sysfs_put(sd->s_parent);
         sd->s_parent = new_parent_sd;
         sysfs_link_sibling(sd);
 
+        mutex_unlock(&sysfs_mutex);
 out:
         mutex_unlock(&new_parent_dentry->d_inode->i_mutex);
         mutex_unlock(&old_parent_dentry->d_inode->i_mutex);
@@ -736,11 +769,12 @@ static int sysfs_dir_open(struct inode *inode, struct file *file)
         struct sysfs_dirent * parent_sd = dentry->d_fsdata;
         struct sysfs_dirent * sd;
 
-        mutex_lock(&dentry->d_inode->i_mutex);
         sd = sysfs_new_dirent("_DIR_", 0, 0);
-        if (sd)
+        if (sd) {
+                mutex_lock(&sysfs_mutex);
                 sysfs_attach_dirent(sd, parent_sd, NULL);
-        mutex_unlock(&dentry->d_inode->i_mutex);
+                mutex_unlock(&sysfs_mutex);
+        }
 
         file->private_data = sd;
         return sd ? 0 : -ENOMEM;
@@ -748,12 +782,11 @@ static int sysfs_dir_open(struct inode *inode, struct file *file)
 
 static int sysfs_dir_close(struct inode *inode, struct file *file)
 {
-        struct dentry * dentry = file->f_path.dentry;
         struct sysfs_dirent * cursor = file->private_data;
 
-        mutex_lock(&dentry->d_inode->i_mutex);
+        mutex_lock(&sysfs_mutex);
         sysfs_unlink_sibling(cursor);
-        mutex_unlock(&dentry->d_inode->i_mutex);
+        mutex_unlock(&sysfs_mutex);
 
         release_sysfs_dirent(cursor);
 
@@ -794,6 +827,8 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
                         i++;
                         /* fallthrough */
                 default:
+                        mutex_lock(&sysfs_mutex);
+
                         pos = &parent_sd->s_children;
                         while (*pos != cursor)
                                 pos = &(*pos)->s_sibling;
@@ -826,6 +861,8 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
                         /* put cursor back in */
                         cursor->s_sibling = *pos;
                         *pos = cursor;
+
+                        mutex_unlock(&sysfs_mutex);
         }
         return 0;
 }
@@ -834,7 +871,6 @@ static loff_t sysfs_dir_lseek(struct file * file, loff_t offset, int origin)
 {
         struct dentry * dentry = file->f_path.dentry;
 
-        mutex_lock(&dentry->d_inode->i_mutex);
         switch (origin) {
                 case 1:
                         offset += file->f_pos;
@@ -842,10 +878,11 @@ static loff_t sysfs_dir_lseek(struct file * file, loff_t offset, int origin)
                         if (offset >= 0)
                                 break;
                 default:
-                        mutex_unlock(&file->f_path.dentry->d_inode->i_mutex);
                         return -EINVAL;
         }
         if (offset != file->f_pos) {
+                mutex_lock(&sysfs_mutex);
+
                 file->f_pos = offset;
                 if (file->f_pos >= 2) {
                         struct sysfs_dirent *sd = dentry->d_fsdata;
@@ -866,8 +903,10 @@ static loff_t sysfs_dir_lseek(struct file * file, loff_t offset, int origin)
                         cursor->s_sibling = *pos;
                         *pos = cursor;
                 }
+
+                mutex_unlock(&sysfs_mutex);
         }
-        mutex_unlock(&dentry->d_inode->i_mutex);
+
         return offset;
 }
 
@@ -933,7 +972,9 @@ struct sysfs_dirent *sysfs_create_shadow_dir(struct kobject *kobj)
         sd->s_elem.dir.kobj = kobj;
         /* point to parent_sd but don't attach to it */
         sd->s_parent = sysfs_get(parent_sd);
+        mutex_lock(&sysfs_mutex);
         sysfs_attach_dirent(sd, NULL, shadow);
+        mutex_unlock(&sysfs_mutex);
 
         d_instantiate(shadow, igrab(inode));
         inc_nlink(inode);