block: zero logical block size leads to infinite loop in set_init_blocksize()

[Maks <mi9992828@gmail.com>]

Hi,

I hit a soft lockup in set_init_blocksize() with a block device whose
logical_block_size was zero.

I understand that logical_block_size == 0 violates the block layer
contract and that the driver which allowed this value needs to be fixed.

However, the generic block code currently turns this invariant violation
into a non-terminating loop:

while (bsize < PAGE_SIZE) {
    if (size & bsize)
        break;
    bsize <<= 1;
}

With bsize == 0, the value never changes.

In my case this resulted in:

watchdog: BUG: soft lockup - CPU#0 stuck for 26s! [(udev-worker):...]
RIP: set_init_blocksize+0x28/0x60

Call Trace:
  blkdev_get_whole+...
  bdev_open+...

Is this considered acceptable behavior for a broken driver, or should
the generic block layer defensively detect this case and fail the open
instead of spinning indefinitely?

If adding such a check is considered worthwhile, I can prepare a patch.

Thanks,
Maks