From: Yosry Ahmed <yosry.ahmed@linux.dev>
To: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Nhat Pham <nphamcs@gmail.com>, Minchan Kim <minchan@kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Brian Geffon <bgeffon@google.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] zsmalloc: use actual object size to detect spans
Date: Wed, 7 Jan 2026 02:10:14 +0000 [thread overview]
Message-ID: <lupjar4x2wz25knuntywor5oyx3ksyhh7g7yv4apmztn47ayep@sncrwg4gjlut> (raw)
In-Reply-To: <5smqbald5bollibqjsvqw2tfngdoiiucurikdgqtz6xjb7u7vz@7p6hskoixaak>
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.
next prev parent reply other threads:[~2026-01-07 2:10 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-06 4:25 Sergey Senozhatsky
2026-01-07 0:23 ` Yosry Ahmed
2026-01-07 0:59 ` Sergey Senozhatsky
2026-01-07 1:37 ` Sergey Senozhatsky
2026-01-07 1:56 ` Yosry Ahmed
2026-01-07 2:06 ` Sergey Senozhatsky
2026-01-07 2:10 ` Yosry Ahmed [this message]
2026-01-07 2:20 ` Sergey Senozhatsky
2026-01-07 2:22 ` Sergey Senozhatsky
2026-01-07 5:19 ` Yosry Ahmed
2026-01-07 5:30 ` Sergey Senozhatsky
2026-01-07 7:12 ` Sergey Senozhatsky
2026-01-07 3:03 ` Sergey Senozhatsky
2026-01-07 5:22 ` Yosry Ahmed
2026-01-07 5:38 ` Sergey Senozhatsky
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