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

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Message-ID: <5smqbald5bollibqjsvqw2tfngdoiiucurikdgqtz6xjb7u7vz@7p6hskoixaak>
Date: Wed, 7 Jan 2026 11:06:09 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Yosry Ahmed <yosry.ahmed@...ux.dev>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Nhat Pham <nphamcs@...il.com>, Minchan Kim <minchan@...nel.org>, 
	Johannes Weiner <hannes@...xchg.org>, Brian Geffon <bgeffon@...gle.com>, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org
Subject: Re: [PATCH] zsmalloc: use actual object size to detect spans

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).