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

From: Yosry Ahmed <yosryahmed@google.com>
To: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Yu Zhao <yuzhao@google.com>, Minchan Kim <minchan@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCHv4 0/4] zsmalloc: fine-grained fullness and new compaction algorithm
Date: Mon, 17 Apr 2023 04:31:11 -0700	[thread overview]
Message-ID: <CAJD7tkbC5drsA2s+=sxXGGm+2RAFXbqs_21KrGaWav_LKjA68w@mail.gmail.com> (raw)
In-Reply-To: <20230417112421.GO25053@google.com>

On Mon, Apr 17, 2023 at 4:24 AM Sergey Senozhatsky
<senozhatsky@chromium.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.