[PATCH 37/44] block: switch partition lookup to use struct block_device

[Christoph Hellwig]

On Fri, Nov 27, 2020 at 01:45:37PM +0100, Jan Kara wrote:
> > At this point the hd_struct is already allocated together with the
> > block_device, and thus only freed after the last block_device reference
> > goes away plus the inode freeing RCU grace period.  So the device model
> > ref to part is indeed gone, but that simply does not matter any more.
> 
> Well, but once device model ref to part is gone, we're going to free the
> bdev inode ref as well. Thus there's nothing which pins the bdev containing
> hd_struct?
> 
> But now as I'm thinking about it you later switch the device model reference
> to just pure inode reference and use igrab() which will reliably return
> NULL if the inode is on it's way to be destroyed so probably we are safe in
> the final state.

igrab always succeeds.  But we should switch to a tryget.