Re: [PATCH] zsmalloc: use actual object size to detect spans

[Yosry Ahmed]

On Wed, Jan 07, 2026 at 11:06:09AM +0900, Sergey Senozhatsky wrote:
> On (26/01/07 01:56), Yosry Ahmed wrote:
> > > I recall us having exactly this idea when we first introduced
> > > zs_obj_{read,write}_end() functions, and I do recall that it
> > > did not work.  Somehow this panics in __memcpy+0xc/0x44.  Let
> > > me dig into it again.
> > 
> > Maybe because at this point we are trying to memcpy() class->size, which
> > already includes ZS_HANDLE_SIZE. So reading after increasing the offset
> > reads ZS_HANDLE_SIZE after class->size.
> 
> Yeah, I guess that falsely hits the spanning path because of extra
> sizeof(unsigned long).

Or the object could be spanning two pages indeed, but we're copying
extra sizeof(unsigned long), that shouldn't crash tho.

I think the changes need to be shuffled around to avoid this, or just
have a combined patch, which would be less pretty.