[3.13.y.z extended stable] Patch "don't bother with {get, put}_write_access() on non-regular files" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

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

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.1.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 1b821784ff3f903f5f725880b0718f723543b4a9 Mon Sep 17 00:00:00 2001
From: Al Viro <viro at zeniv.linux.org.uk>
Date: Fri, 14 Mar 2014 10:56:20 -0400
Subject: 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 at zeniv.linux.org.uk>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/file_table.c |  4 ++--
 fs/open.c       | 26 +++++++-------------------
 2 files changed, 9 insertions(+), 21 deletions(-)

diff --git a/fs/file_table.c b/fs/file_table.c
index 5fff903..0e5202f 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -208,10 +208,10 @@ 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 4b3e1ed..159f3e7 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -641,23 +641,12 @@ 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;
 }

@@ -690,12 +679,11 @@ 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;
@@ -738,7 +726,6 @@ static int do_dentry_open(struct file *f,
 cleanup_all:
 	fops_put(f->f_op);
 	if (f->f_mode & FMODE_WRITE) {
-		put_write_access(inode);
 		if (!special_file(inode->i_mode)) {
 			/*
 			 * We don't consider this a real
@@ -746,6 +733,7 @@ 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);
 		}
--
1.9.1