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authorDave Hansen <haveblue@us.ibm.com>2008-02-15 14:37:48 -0800
committerAl Viro <viro@zeniv.linux.org.uk>2008-04-19 00:29:25 -0400
commit4a3fd211ccfc08a88edc824300e25a87785c6a5f (patch)
tree99f1a76a99fa78464b8de731f7fdb5bcc9667a5e /fs/file_table.c
parent42a74f206b914db13ee1f5ae932dcd91a77c8579 (diff)
downloadlwn-4a3fd211ccfc08a88edc824300e25a87785c6a5f.tar.gz
lwn-4a3fd211ccfc08a88edc824300e25a87785c6a5f.zip
[PATCH] r/o bind mounts: elevate write count for open()s
This is the first really tricky patch in the series. It elevates the writer count on a mount each time a non-special file is opened for write. We used to do this in may_open(), but Miklos pointed out that __dentry_open() is used as well to create filps. This will cover even those cases, while a call in may_open() would not have. There is also an elevated count around the vfs_create() call in open_namei(). See the comments for more details, but we need this to fix a 'create, remount, fail r/w open()' race. Some filesystems forego the use of normal vfs calls to create struct files. Make sure that these users elevate the mnt writer count because they will get __fput(), and we need to make sure they're balanced. Acked-by: Al Viro <viro@ZenIV.linux.org.uk> Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Dave Hansen <haveblue@us.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/file_table.c')
-rw-r--r--fs/file_table.c14
1 files changed, 14 insertions, 0 deletions
diff --git a/fs/file_table.c b/fs/file_table.c
index 3f73eb1f195a..71efc7000226 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -199,6 +199,17 @@ int init_file(struct file *file, struct vfsmount *mnt, struct dentry *dentry,
file->f_mapping = dentry->d_inode->i_mapping;
file->f_mode = mode;
file->f_op = fop;
+
+ /*
+ * These mounts don't really matter in practice
+ * for r/o bind mounts. They aren't userspace-
+ * visible. We do this for consistency, and so
+ * that we can do debugging checks at __fput()
+ */
+ if ((mode & FMODE_WRITE) && !special_file(dentry->d_inode->i_mode)) {
+ error = mnt_want_write(mnt);
+ WARN_ON(error);
+ }
return error;
}
EXPORT_SYMBOL(init_file);
@@ -221,10 +232,13 @@ EXPORT_SYMBOL(fput);
*/
void drop_file_write_access(struct file *file)
{
+ struct vfsmount *mnt = file->f_path.mnt;
struct dentry *dentry = file->f_path.dentry;
struct inode *inode = dentry->d_inode;
put_write_access(inode);
+ if (!special_file(inode->i_mode))
+ mnt_drop_write(mnt);
}
EXPORT_SYMBOL_GPL(drop_file_write_access);