[PATCH RFC 02/16] proc: add pde_pin() and pde_unpin()

@@ -206,6 +206,18 @@ static void unuse_pde(struct proc_dir_entry *pde)
 		complete(pde->pde_unload_completion);
 }
 
+/* Pin an entry that can go away around a call into it, see use_pde(). */
+static bool pde_pin(struct proc_dir_entry *pde)
+{
+	return pde_is_permanent(pde) || use_pde(pde);
+}
+
+static void pde_unpin(struct proc_dir_entry *pde)
+{
+	if (!pde_is_permanent(pde))
+		unuse_pde(pde);
+}
+
 /*
  * At most 2 contexts can enter this function: the one doing the last
  * close on the descriptor and whoever is deleting PDE itself.

@@ -275,14 +287,12 @@ void proc_entry_rundown(struct proc_dir_entry *de)
 static loff_t proc_reg_llseek(struct file *file, loff_t offset, int whence)
 {
 	struct proc_dir_entry *pde = PDE(file_inode(file));
-	loff_t rv = -EINVAL;
+	loff_t rv;
 
-	if (pde_is_permanent(pde)) {
-		return pde->proc_ops->proc_lseek(file, offset, whence);
-	} else if (use_pde(pde)) {
-		rv = pde->proc_ops->proc_lseek(file, offset, whence);
-		unuse_pde(pde);
-	}
+	if (!pde_pin(pde))
+		return -EINVAL;
+	rv = pde->proc_ops->proc_lseek(file, offset, whence);
+	pde_unpin(pde);
 	return rv;
 }
 

@@ -291,13 +301,10 @@ static ssize_t proc_reg_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 	struct proc_dir_entry *pde = PDE(file_inode(iocb->ki_filp));
 	ssize_t ret;
 
-	if (pde_is_permanent(pde))
-		return pde->proc_ops->proc_read_iter(iocb, iter);
-
-	if (!use_pde(pde))
+	if (!pde_pin(pde))
 		return -EIO;
 	ret = pde->proc_ops->proc_read_iter(iocb, iter);
-	unuse_pde(pde);
+	pde_unpin(pde);
 	return ret;
 }
 

@@ -312,14 +319,12 @@ static ssize_t pde_read(struct proc_dir_entry *pde, struct file *file, char __us
 static ssize_t proc_reg_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 {
 	struct proc_dir_entry *pde = PDE(file_inode(file));
-	ssize_t rv = -EIO;
+	ssize_t rv;
 
-	if (pde_is_permanent(pde)) {
-		return pde_read(pde, file, buf, count, ppos);
-	} else if (use_pde(pde)) {
-		rv = pde_read(pde, file, buf, count, ppos);
-		unuse_pde(pde);
-	}
+	if (!pde_pin(pde))
+		return -EIO;
+	rv = pde_read(pde, file, buf, count, ppos);
+	pde_unpin(pde);
 	return rv;
 }
 

@@ -334,14 +339,12 @@ static ssize_t pde_write(struct proc_dir_entry *pde, struct file *file, const ch
 static ssize_t proc_reg_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
 {
 	struct proc_dir_entry *pde = PDE(file_inode(file));
-	ssize_t rv = -EIO;
+	ssize_t rv;
 
-	if (pde_is_permanent(pde)) {
-		return pde_write(pde, file, buf, count, ppos);
-	} else if (use_pde(pde)) {
-		rv = pde_write(pde, file, buf, count, ppos);
-		unuse_pde(pde);
-	}
+	if (!pde_pin(pde))
+		return -EIO;
+	rv = pde_write(pde, file, buf, count, ppos);
+	pde_unpin(pde);
 	return rv;
 }
 

@@ -356,14 +359,12 @@ static __poll_t pde_poll(struct proc_dir_entry *pde, struct file *file, struct p
 static __poll_t proc_reg_poll(struct file *file, struct poll_table_struct *pts)
 {
 	struct proc_dir_entry *pde = PDE(file_inode(file));
-	__poll_t rv = DEFAULT_POLLMASK;
+	__poll_t rv;
 
-	if (pde_is_permanent(pde)) {
-		return pde_poll(pde, file, pts);
-	} else if (use_pde(pde)) {
-		rv = pde_poll(pde, file, pts);
-		unuse_pde(pde);
-	}
+	if (!pde_pin(pde))
+		return DEFAULT_POLLMASK;
+	rv = pde_poll(pde, file, pts);
+	pde_unpin(pde);
 	return rv;
 }
 

@@ -378,14 +379,12 @@ static long pde_ioctl(struct proc_dir_entry *pde, struct file *file, unsigned in
 static long proc_reg_unlocked_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
 	struct proc_dir_entry *pde = PDE(file_inode(file));
-	long rv = -ENOTTY;
+	long rv;
 
-	if (pde_is_permanent(pde)) {
-		return pde_ioctl(pde, file, cmd, arg);
-	} else if (use_pde(pde)) {
-		rv = pde_ioctl(pde, file, cmd, arg);
-		unuse_pde(pde);
-	}
+	if (!pde_pin(pde))
+		return -ENOTTY;
+	rv = pde_ioctl(pde, file, cmd, arg);
+	pde_unpin(pde);
 	return rv;
 }
 

@@ -401,13 +400,12 @@ static long pde_compat_ioctl(struct proc_dir_entry *pde, struct file *file, unsi
 static long proc_reg_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
 	struct proc_dir_entry *pde = PDE(file_inode(file));
-	long rv = -ENOTTY;
-	if (pde_is_permanent(pde)) {
-		return pde_compat_ioctl(pde, file, cmd, arg);
-	} else if (use_pde(pde)) {
-		rv = pde_compat_ioctl(pde, file, cmd, arg);
-		unuse_pde(pde);
-	}
+	long rv;
+
+	if (!pde_pin(pde))
+		return -ENOTTY;
+	rv = pde_compat_ioctl(pde, file, cmd, arg);
+	pde_unpin(pde);
 	return rv;
 }
 #else

@@ -425,14 +423,12 @@ static int pde_mmap(struct proc_dir_entry *pde, struct file *file, struct vm_are
 static int proc_reg_mmap(struct file *file, struct vm_area_struct *vma)
 {
 	struct proc_dir_entry *pde = PDE(file_inode(file));
-	int rv = -EIO;
+	int rv;
 
-	if (pde_is_permanent(pde)) {
-		return pde_mmap(pde, file, vma);
-	} else if (use_pde(pde)) {
-		rv = pde_mmap(pde, file, vma);
-		unuse_pde(pde);
-	}
+	if (!pde_pin(pde))
+		return -EIO;
+	rv = pde_mmap(pde, file, vma);
+	pde_unpin(pde);
 	return rv;
 }
 

@@ -457,14 +453,12 @@ proc_reg_get_unmapped_area(struct file *file, unsigned long orig_addr,
 			   unsigned long flags)
 {
 	struct proc_dir_entry *pde = PDE(file_inode(file));
-	unsigned long rv = -EIO;
+	unsigned long rv;
 
-	if (pde_is_permanent(pde)) {
-		return pde_get_unmapped_area(pde, file, orig_addr, len, pgoff, flags);
-	} else if (use_pde(pde)) {
-		rv = pde_get_unmapped_area(pde, file, orig_addr, len, pgoff, flags);
-		unuse_pde(pde);
-	}
+	if (!pde_pin(pde))
+		return -EIO;
+	rv = pde_get_unmapped_area(pde, file, orig_addr, len, pgoff, flags);
+	pde_unpin(pde);
 	return rv;
 }