Re: [PATCH] mm/highmem: VM_BUG_ON() if offset + len > PAGE_SIZE

[Fabio M. De Francesco]

On martedì 26 aprile 2022 21:34:12 CEST Andrew Morton wrote:
> On Tue, 26 Apr 2022 21:30:20 +0200 "Fabio M. De Francesco" 
<fmdefrancesco@xxxxxxxxx> wrote:
> 
> > Add VM_BUG_ON() bounds checking to make sure that, if "offset + len>
> > PAGE_SIZE", memset() does not corrupt data in adjacent pages.
> > 
> 
> hm, why?  To match all the other functions in there?
> 
> I suppose that's logical.  Or we could just delete all the other
> VM_BUG_ON()s.  Have any of them proven to be at all useful?
> 
I am not so sure about it being so useful. I just noted that memzero_page() 
is the only function of that family that is implemented with no 
VM_BUG_ON(). I have no actual proofs of usefulness :( 

This is why yesterday I sent an "RFC Patch" (please see  
https://lore.kernel.org/lkml/20220424104806.25396-1-fmdefrancesco@xxxxxxxxx/

Soon after sending it I thought that VM_WARN_ON_ONCE() could have been 
better suited, but Ira Weiny wrote to use VM_BUG_ON() for consistency.

Now I could either delete all other VM_BUG_ON() or replace them with 
VM_WARN_ON_ONCE() (or some other macro). 

Ah, a third solution might be to leave highmem.h as it is now :)

What do you prefer?

Thanks,

Fabio