Re: [PATCH] fs: buffer: set the expression type to unsigned long in folio_create_buffers()

[Jan Kara <jack@suse.cz>]

On Tue 16-07-24 16:51:17, Matthew Wilcox wrote:
> On Tue, Jul 16, 2024 at 06:41:49PM +0300, Sergey Shtylyov wrote:
> >    And here we'll have at least one potential problem (that you neglected
> > to describe): with 1 << 31, that 1 will land in a sign bit and then, when
> > it's implicitly cast to *unsigned long*, the 32-bit value will be sign-
> > extended to 64-bit on 64-bit arches) and then we'll have an incorrect size
> > (0xffffffff80000000) passed to create_empty_buffers()...
> 
> Tell me more about this block device you have with a 2GB block size ... ?
> 
> (ie note that this is a purely theoretical issue)

Yeah, this just does not make huge amount of sense. Maybe a proper fix
would be to just make blocksize uint? There are a lot of places where
blocksize is actually stored in a 32-bit type...

								Honza

> 
> > > to use 1UL instead.
> > 
> >    Perphas was worth noting that using 1UL saves us 1 movsx instruction on
> > x86_64...
> 
> That is a worthwhile addition to the change log.
> 
> Also, you should cc the person who wrote that code, ie me.
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR