On Tue 13-04-10 14:33:01, Kirill A. Shutemov wrote: > I've got NULL-pointer dereference in __mark_inode_dirty() on chmod() > for MTD device node. wb->bdi was NULL in this case. > > During investigation I've found that MTD subsystem rewrites > file->f_mapping->backing_dev_info on openning to get mmap() work on > MMU-less systems. But in fact it rewrites > inode->i_mapping->backing_dev_info too, since inode->i_mapping == > file->f_mapping (see __dentry_open() in fs/open.c). It breaks > writeback of inode changes. I think the right trick is to not overwrite file->f_mapping->backing_dev_info but rather change already file->f_mapping. For example drivers/char/raw.c does this. Then you'll stop having problems with writeback code going wild. > I guess the right way to fix this is changing of __dentry_open() to > create _copy_ of i_mapping to assign to f_mapping since in common case > f_mapping != i_mapping. But I'm not sure were the copy should be > freed. No, in most cases we will leave f_mapping == i_mapping so copying i_mapping would be an overkill. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
