On Wed, 2007-09-26 at 01:14 +0200, Miklos Szeredi wrote:
> I get this at umount, if there was a failed open():
>
> WARNING: at fs/namespace.c:586 __mntput()
>
> I think the problem is that may_open() calls mnt_want_write(), but if
> open doesn't succeed, mnt_drop_write() will not be called.
Does this help? I'm also thinking that we should change the open_namei*
functions to simply return 'struct file *'. Those are the only users
other than NFS, and forcing the return of a file like that will force
users to do the fput() on it if they don't want it any more. We'd just
need to make sure no new may_open() users pop up. Any thoughts on that?
--
The r/o bind mount patches have an error in them:
they unconditionally take a mnt_want_write() on
all may_open() requests for writeable files. They
mistakenly do not mnt_drop_write() if may_open()
encounters an error.
---
lxc-dave/fs/namei.c | 39 ++++++++++++++++++++++++++++++---------
1 file changed, 30 insertions(+), 9 deletions(-)
diff -puN fs/namei.c~drop-write-if-may_open-fails fs/namei.c
--- lxc/fs/namei.c~drop-write-if-may_open-fails 2007-09-25 18:16:59.000000000 -0700
+++ lxc-dave/fs/namei.c 2007-09-25 18:16:59.000000000 -0700
@@ -1594,11 +1594,23 @@ int vfs_create(struct inode *dir, struct
return error;
}
+/*
+ * If you call this with FMODE_WRITE set in flag,
+ * and get a successful return, you will have
+ * acquired a write on nd->mnt.
+ *
+ * Basically, if you use this function, you either
+ * need to fix up that write count manually, or just
+ * return a 'struct file' from your function. When
+ * you __fput() that 'struct file' it will get fixed
+ * up automatically.
+ */
int may_open(struct nameidata *nd, int acc_mode, int flag)
{
struct dentry *dentry = nd->dentry;
struct inode *inode = dentry->d_inode;
int error;
+ int took_mnt_write = 0;
if (!inode)
return -ENOENT;
@@ -1624,42 +1636,48 @@ int may_open(struct nameidata *nd, int a
} else if (flag & FMODE_WRITE) {
/*
* effectively: !special_file()
- * balanced by __fput()
+ * Balanced by __fput() and
+ * released on error at the end
+ * of this function.
*/
error = mnt_want_write(nd->mnt);
if (error)
return error;
+ took_mnt_write = 1;
}
error = vfs_permission(nd, acc_mode);
if (error)
- return error;
+ goto out_err;
/*
* An append-only file must be opened in append mode for writing.
*/
if (IS_APPEND(inode)) {
+ error = -EPERM;
if ((flag & FMODE_WRITE) && !(flag & O_APPEND))
- return -EPERM;
+ goto out_err;
+ error = -EPERM;
if (flag & O_TRUNC)
- return -EPERM;
+ goto out_err;
}
/* O_NOATIME can only be set by the owner or superuser */
+ error = -EPERM;
if (flag & O_NOATIME)
if (!is_owner_or_cap(inode))
- return -EPERM;
+ goto out_err;
/*
* Ensure there are no outstanding leases on the file.
*/
error = break_lease(inode, flag);
if (error)
- return error;
+ goto out_err;
if (flag & O_TRUNC) {
error = get_write_access(inode);
if (error)
- return error;
+ goto out_err;
/*
* Refuse to truncate files with mandatory locks held on them.
@@ -1672,12 +1690,15 @@ int may_open(struct nameidata *nd, int a
}
put_write_access(inode);
if (error)
- return error;
+ goto out_err;
} else
if (flag & FMODE_WRITE)
DQUOT_INIT(inode);
- return 0;
+out_err:
+ if (error && took_mnt_write)
+ mnt_drop_write(nd->mnt);
+ return error;
}
static int open_namei_create(struct nameidata *nd, struct path *path,
-- Dave
-
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