[RFC][PATCH 19/20] elevate writer count for custom 'struct file'

[Dave Hansen]

Some filesystems forego the vfs and may_open() and create their
own 'struct file's.  Any of these users which set the write flag
on the file will cause an extra mnt_drop_write() on __fput(),
thus dropping the reference count too low.

These users tend to have artifical in-kernel vfsmounts which
aren't really exposed to userspace and can't be remounted, but
this patch is included for completeness and so that the warnings
don't trip over these cases.

Signed-off-by: Dave Hansen <haveblue@xxxxxxxxxx>
---

 lxc-dave/fs/hugetlbfs/inode.c |    2 ++
 lxc-dave/mm/shmem.c           |    2 ++
 lxc-dave/mm/tiny-shmem.c      |    2 ++
 lxc-dave/net/socket.c         |    3 +++
 4 files changed, 9 insertions(+)

diff -puN fs/hugetlbfs/inode.c~fix-__fput-rev2 fs/hugetlbfs/inode.c
--- lxc/fs/hugetlbfs/inode.c~fix-__fput-rev2	2006-06-16 15:58:11.000000000 -0700
+++ lxc-dave/fs/hugetlbfs/inode.c	2006-06-16 15:58:11.000000000 -0700
@@ -790,6 +790,8 @@ struct file *hugetlb_zero_setup(size_t s
 	file->f_mapping = inode->i_mapping;
 	file->f_op = &hugetlbfs_file_operations;
 	file->f_mode = FMODE_WRITE | FMODE_READ;
+	error = mnt_want_write(hugetlbfs_vfsmount);
+	WARN_ON(error);
 	return file;
 
 out_inode:
diff -puN mm/shmem.c~fix-__fput-rev2 mm/shmem.c
--- lxc/mm/shmem.c~fix-__fput-rev2	2006-06-16 15:58:11.000000000 -0700
+++ lxc-dave/mm/shmem.c	2006-06-16 15:58:11.000000000 -0700
@@ -2324,6 +2324,8 @@ struct file *shmem_file_setup(char *name
 	file->f_mapping = inode->i_mapping;
 	file->f_op = &shmem_file_operations;
 	file->f_mode = FMODE_WRITE | FMODE_READ;
+	error = mnt_want_write(shm_mnt);
+	WARN_ON(error);
 	return file;
 
 close_file:
diff -puN mm/tiny-shmem.c~fix-__fput-rev2 mm/tiny-shmem.c
--- lxc/mm/tiny-shmem.c~fix-__fput-rev2	2006-06-16 15:58:11.000000000 -0700
+++ lxc-dave/mm/tiny-shmem.c	2006-06-16 15:58:11.000000000 -0700
@@ -88,6 +88,8 @@ struct file *shmem_file_setup(char *name
 	file->f_mapping = inode->i_mapping;
 	file->f_op = &ramfs_file_operations;
 	file->f_mode = FMODE_WRITE | FMODE_READ;
+	error = mnt_want_write(shm_mnt);
+	WARN_ON(error);
 
 	/* notify everyone as to the change of file size */
 	error = do_truncate(dentry, size, 0, file);
diff -puN net/socket.c~fix-__fput-rev2 net/socket.c
--- lxc/net/socket.c~fix-__fput-rev2	2006-06-16 15:58:11.000000000 -0700
+++ lxc-dave/net/socket.c	2006-06-16 15:58:11.000000000 -0700
@@ -395,6 +395,7 @@ static int sock_attach_fd(struct socket 
 {
 	struct qstr this;
 	char name[32];
+	int error;
 
 	this.len = sprintf(name, "[%lu]", SOCK_INODE(sock)->i_ino);
 	this.name = name;
@@ -415,6 +416,8 @@ static int sock_attach_fd(struct socket 
 	file->f_flags = O_RDWR;
 	file->f_pos = 0;
 	file->private_data = sock;
+	error = mnt_want_write(sock_mnt);
+	WARN_ON(error);
 
 	return 0;
 }
_
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