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SubjectRe: [PATCH] loop: fput() called in loop_clr_fd() may cause bd_mutex recursive locking
On Sun, Dec 18, 2011 at 01:19:28AM +0300, Sergey Senozhatsky wrote:

> Sorry, why is that a false positive?
>
> blkdev_put() calls lo_release() while holding bd_mutex,
> lo_release() calls loop_clr_fd() -> fput(). fput() once again
> attempts to grub already held bd_mutex calling blkdev_put().
> Looks like a recursion to me.

Because of this:
/* Avoid recursion */
f = file;
while (is_loop_device(f)) {
struct loop_device *l;
if (f->f_mapping->host->i_bdev == bdev)
goto out_putf;
l = f->f_mapping->host->i_bdev->bd_disk->private_data;
if (l->lo_state == Lo_unbound) {
error = -EINVAL;
goto out_putf;
}
f = l->lo_backing_file;
}
in loop_set_fd(). Think of it for a minute - if we could run into the
same bdev in that recursion, what would have happened on read() from
that sucker? So yes, it is a false positive. And your patch would
simply leave the underlying device opened, with all the consequences...

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