procfs: preparations for remove_proc_entry() race fixes

* leave ->proc_fops alone; make ->pde_users negative instead
* trim pde_opener
* move relevant code in fs/proc/inode.c
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/proc/generic.c

@@ -39,7 +39,7 @@ static int proc_match(unsigned int len, const char *name, struct proc_dir_entry
 /* buffer size is one page but our output routines use some slack for overruns */
 #define PROC_BLOCK_SIZE	(PAGE_SIZE - 1024)
 
-static ssize_t
+ssize_t
 __proc_file_read(struct file *file, char __user *buf, size_t nbytes,
 	       loff_t *ppos)
 {
@@ -171,48 +171,6 @@ __proc_file_read(struct file *file, char __user *buf, size_t nbytes,
 	return retval;
 }
 
-static ssize_t
-proc_file_read(struct file *file, char __user *buf, size_t nbytes,
-	       loff_t *ppos)
-{
-	struct proc_dir_entry *pde = PDE(file_inode(file));
-	ssize_t rv = -EIO;
-
-	spin_lock(&pde->pde_unload_lock);
-	if (!pde->proc_fops) {
-		spin_unlock(&pde->pde_unload_lock);
-		return rv;
-	}
-	pde->pde_users++;
-	spin_unlock(&pde->pde_unload_lock);
-
-	rv = __proc_file_read(file, buf, nbytes, ppos);
-
-	pde_users_dec(pde);
-	return rv;
-}
-
-static loff_t
-proc_file_lseek(struct file *file, loff_t offset, int orig)
-{
-	loff_t retval = -EINVAL;
-	switch (orig) {
-	case 1:
-		offset += file->f_pos;
-	/* fallthrough */
-	case 0:
-		if (offset < 0 || offset > MAX_NON_LFS)
-			break;
-		file->f_pos = retval = offset;
-	}
-	return retval;
-}
-
-static const struct file_operations proc_file_operations = {
-	.llseek		= proc_file_lseek,
-	.read		= proc_file_read,
-};
-
 static int proc_notify_change(struct dentry *dentry, struct iattr *iattr)
 {
 	struct inode *inode = dentry->d_inode;
@@ -722,41 +680,6 @@ void pde_put(struct proc_dir_entry *pde)
 		free_proc_entry(pde);
 }
 
-static void entry_rundown(struct proc_dir_entry *de)
-{
-	spin_lock(&de->pde_unload_lock);
-	/*
-	 * Stop accepting new callers into module. If you're
-	 * dynamically allocating ->proc_fops, save a pointer somewhere.
-	 */
-	de->proc_fops = NULL;
-	/* Wait until all existing callers into module are done. */
-	if (de->pde_users > 0) {
-		DECLARE_COMPLETION_ONSTACK(c);
-
-		if (!de->pde_unload_completion)
-			de->pde_unload_completion = &c;
-
-		spin_unlock(&de->pde_unload_lock);
-
-		wait_for_completion(de->pde_unload_completion);
-
-		spin_lock(&de->pde_unload_lock);
-	}
-
-	while (!list_empty(&de->pde_openers)) {
-		struct pde_opener *pdeo;
-
-		pdeo = list_first_entry(&de->pde_openers, struct pde_opener, lh);
-		list_del(&pdeo->lh);
-		spin_unlock(&de->pde_unload_lock);
-		pdeo->release(pdeo->inode, pdeo->file);
-		kfree(pdeo);
-		spin_lock(&de->pde_unload_lock);
-	}
-	spin_unlock(&de->pde_unload_lock);
-}
-
 /*
  * Remove a /proc entry and free it if it's not currently in use.
  */
@@ -788,7 +711,7 @@ void remove_proc_entry(const char *name, struct proc_dir_entry *parent)
 		return;
 	}
 
-	entry_rundown(de);
+	proc_entry_rundown(de);
 
 	if (S_ISDIR(de->mode))
 		parent->nlink--;
@@ -837,7 +760,7 @@ int remove_proc_subtree(const char *name, struct proc_dir_entry *parent)
 		}
 		spin_unlock(&proc_subdir_lock);
 
-		entry_rundown(de);
+		proc_entry_rundown(de);
 		next = de->parent;
 		if (S_ISDIR(de->mode))
 			next->nlink--;

fs/proc/internal.h

@@ -151,12 +151,13 @@ int proc_readdir_de(struct proc_dir_entry *de, struct file *filp, void *dirent,
 		filldir_t filldir);
 
 struct pde_opener {
-	struct inode *inode;
 	struct file *file;
-	int (*release)(struct inode *, struct file *);
 	struct list_head lh;
 };
-void pde_users_dec(struct proc_dir_entry *pde);
+
+ssize_t __proc_file_read(struct file *, char __user *, size_t, loff_t *);
+extern const struct file_operations proc_file_operations;
+void proc_entry_rundown(struct proc_dir_entry *);
 
 extern spinlock_t proc_subdir_lock;
 

include/linux/proc_fs.h

@@ -60,20 +60,13 @@ struct proc_dir_entry {
 	kgid_t gid;
 	loff_t size;
 	const struct inode_operations *proc_iops;
-	/*
-	 * NULL ->proc_fops means "PDE is going away RSN" or
-	 * "PDE is just created". In either case, e.g. ->read_proc won't be
-	 * called because it's too late or too early, respectively.
-	 *
-	 * If you're allocating ->proc_fops dynamically, save a pointer
-	 * somewhere.
-	 */
 	const struct file_operations *proc_fops;
 	struct proc_dir_entry *next, *parent, *subdir;
 	void *data;
 	read_proc_t *read_proc;
 	atomic_t count;		/* use count */
-	int pde_users;	/* number of callers into module in progress */
+	int pde_users;	/* number of callers into module in progress; */
+			/* negative -> it's going away RSN */
 	struct completion *pde_unload_completion;
 	struct list_head pde_openers;	/* who did ->open, but not ->release */
 	spinlock_t pde_unload_lock; /* proc_fops checks and pde_users bumps */