From: Al Viro <viro@zeniv.linux.org.uk>
Date: Fri, 14 Mar 2014 14:56:20 +0000 (-0400)
Subject: don't bother with {get,put}_write_access() on non-regular files
X-Git-Url: http://git.mmlx.us/?a=commitdiff_plain;h=68ad89c73da6085d14e18f18ec7298821d408b2d;p=linux-edison.git

don't bother with {get,put}_write_access() on non-regular files

commit dd20908a8a06b22c171f6c3fcdbdbd65bed07505 upstream.

it's pointless and actually leads to wrong behaviour in at least one
moderately convoluted case (pipe(), close one end, try to get to
another via /proc/*/fd and run into ETXTBUSY).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/fs/file_table.c b/fs/file_table.c
index 485dc0eddd6..54a34be444f 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -211,10 +211,10 @@ static void drop_file_write_access(struct file *file)
 	struct dentry *dentry = file->f_path.dentry;
 	struct inode *inode = dentry->d_inode;
 
-	put_write_access(inode);
-
 	if (special_file(inode->i_mode))
 		return;
+
+	put_write_access(inode);
 	if (file_check_writeable(file) != 0)
 		return;
 	__mnt_drop_write(mnt);
diff --git a/fs/open.c b/fs/open.c
index 8c741002f94..86092bde31f 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -628,23 +628,12 @@ out:
 static inline int __get_file_write_access(struct inode *inode,
 					  struct vfsmount *mnt)
 {
-	int error;
-	error = get_write_access(inode);
+	int error = get_write_access(inode);
 	if (error)
 		return error;
-	/*
-	 * Do not take mount writer counts on
-	 * special files since no writes to
-	 * the mount itself will occur.
-	 */
-	if (!special_file(inode->i_mode)) {
-		/*
-		 * Balanced in __fput()
-		 */
-		error = __mnt_want_write(mnt);
-		if (error)
-			put_write_access(inode);
-	}
+	error = __mnt_want_write(mnt);
+	if (error)
+		put_write_access(inode);
 	return error;
 }
 
@@ -677,12 +666,11 @@ static int do_dentry_open(struct file *f,
 
 	path_get(&f->f_path);
 	inode = f->f_inode = f->f_path.dentry->d_inode;
-	if (f->f_mode & FMODE_WRITE) {
+	if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) {
 		error = __get_file_write_access(inode, f->f_path.mnt);
 		if (error)
 			goto cleanup_file;
-		if (!special_file(inode->i_mode))
-			file_take_write(f);
+		file_take_write(f);
 	}
 
 	f->f_mapping = inode->i_mapping;
@@ -723,7 +711,6 @@ cleanup_all:
 	fops_put(f->f_op);
 	file_sb_list_del(f);
 	if (f->f_mode & FMODE_WRITE) {
-		put_write_access(inode);
 		if (!special_file(inode->i_mode)) {
 			/*
 			 * We don't consider this a real
@@ -731,6 +718,7 @@ cleanup_all:
 			 * because it all happenend right
 			 * here, so just reset the state.
 			 */
+			put_write_access(inode);
 			file_reset_write(f);
 			__mnt_drop_write(f->f_path.mnt);
 		}