Re: [Linux-cachefs] [PATCH v2 2/2] netfs: Fix dodgy maths

[JeffleXu]

On 11/5/22 12:38 AM, David Howells wrote:
> Fix the dodgy maths in netfs_rreq_unlock_folios().  start_page could be
> inside the folio, in which case the calculation of pgpos will be come up
> with a negative number (though for the moment rreq->start is rounded down
> earlier and folios would have to get merged whilst locked)
> 
> Alter how this works to just frame the tracking in terms of absolute file
> positions, rather than offsets from the start of the I/O request.  This
> simplifies the maths and makes it easier to follow.
> 
> Fix the issue by using folio_pos() and folio_size() to calculate the end
> position of the page.
> 
> Fixes: 3d3c95046742 ("netfs: Provide readahead and readpage netfs helpers")
> Reported-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: Jeff Layton <jlayton@xxxxxxxxxx>
> cc: linux-cachefs@xxxxxxxxxx
> cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Link: https://lore.kernel.org/r/Y2SJw7w1IsIik3nb@xxxxxxxxxxxxxxxxxxxx/

Reviewed-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>

-- 
Thanks,
Jingbo