linux-kernel - Re: [PATCHv4 0/4] zsmalloc: fine-grained fullness and new compaction algorithm

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAJD7tkbC5drsA2s+=sxXGGm+2RAFXbqs_21KrGaWav_LKjA68w@mail.gmail.com>
Date:   Mon, 17 Apr 2023 04:31:11 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Yu Zhao <yuzhao@...gle.com>, Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv4 0/4] zsmalloc: fine-grained fullness and new compaction algorithm

On Mon, Apr 17, 2023 at 4:24 AM Sergey Senozhatsky
<senozhatsky@...omium.org> wrote:
>
> On (23/04/17 04:16), Yosry Ahmed wrote:
> > > That's a good question to which I don't have an answer. We can list_add()
> > > the same zspage twice, unlocking the pool after first list_add() so that
> > > another process (including another zs_compact()) can do something to that
> > > zspage. The answer is somewhere between these lines, I guess.
> >
> > But the first list_add() is (in this case) the correct add, so we
> > expect other processes to be able to access the zspage after the first
> > list_add() anyway, right?
>
> Correct. Compaction also can unlock pool->lock and schedule() so that
> another process can access the source zspage, when compaction gets
> scheduled it can attempt putback/unlock the same zspage one more time
> (the zspage may not even exist at this point, I assume).

Good point, that could very well be where the corruption is coming
from. Thanks for pointing this out.