Re: [PATCH 14/20] block: remove the nr_sects field in struct hd_struct

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Fri, Nov 20, 2020 at 04:32:53PM +0100, Christoph Hellwig wrote:
> On Fri, Nov 20, 2020 at 12:21:21PM +0100, Jan Kara wrote:
> > > > AFAICT bd_size_lock is pointless after these changes so we can just 
> > > > remove
> > > > it?
> > > 
> > > I don't think it is, as reuqiring bd_mutex for size updates leads to
> > > rather awkward lock ordering problems.
> > 
> > OK, let me ask differently: What is bd_size_lock protecting now? Ah, I see,
> > on 32-bit it is needed to prevent torn writes to i_size, right?
> 
> Exactly.  In theory we could skip it for 64-bit, but as updating the
> size isn't a fast path, and struct block_device isn't super size critical
> I'd rather keep the same code for 32 vs 64-bit builds.

Is it better to switch to i_size_write() / i_size_read()?