Re: [PATCH 3/6] iomap: Check iblocksize before transforming page->private

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On  9:05 24/06, Christoph Hellwig wrote:
> On Fri, Jun 21, 2019 at 02:28:25PM -0500, Goldwyn Rodrigues wrote:
> > From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
> > 
> > btrfs uses page->private as well to store extent_buffer. Make
> > the check stricter to make sure we are using page->private for iop by
> > comparing iblocksize < PAGE_SIZE.
> > 
> > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
> 
> If btrfs uses page->private itself and also uses functions that call
> to_iomap_page we have a major problem, as we now have a usage conflict.
> 
> How do you end up here?  
> 

Btrfs uses page->private to identify which extent_buffer it belongs to.
So, if you read, it fills the page->private. Then you try to write to
it, iomap will assume it to be iomap_page pointer.

I don't think we can move extent_buffer out of page->private for btrfs.
Any other ideas?

-- 
Goldwyn



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