At Wed, 4 Oct 2006 12:47:19 +0200,
Karsten Wiese wrote:
>
> Am Mittwoch, 4. Oktober 2006 11:22 schrieb Takashi Iwai:
> >
> > It should call snd_card_free_when_closed() instead.
> >
> IMHO, that would just make sure that the bug happens.
> Please see my annotations, starting with // in:
>
> void fastcall __fput(struct file *file)
> {
> struct dentry *dentry = file->f_dentry;
> struct vfsmount *mnt = file->f_vfsmnt;
> struct inode *inode = dentry->d_inode;
>
> might_sleep();
>
> fsnotify_close(file);
> /*
> * The function eventpoll_release() should be the first called
> * in the file cleanup chain.
> */
> eventpoll_release(file);
> locks_remove_flock(file);
>
> if (file->f_op && file->f_op->release)
> file->f_op->release(inode, file);
> // Here snd_hwdep_release() is called.
> // snd_hwdep_release() calls snd_card_file_remove().
> // snd_card_file_remove() sees card->free_on_last_close ist set,
> // calls snd_card_do_free().
> // snd_card_do_free frees file->f_op but doesn't set it NULL.
> //
> security_file_free(file);
> if (unlikely(inode->i_cdev != NULL))
> cdev_put(inode->i_cdev);
> fops_put(file->f_op);
> // file->f_op has already been freeed!
> // fops_put(file->f_op) is likely to oops.
Yes, this looks like an invalid access.
The problem is that we use kmalloc for allocating a dummy f_op.
IMO, the simlest solution is to use a static dummy f_op.
Takashi
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