linux-kernel - Re: [regression] oops on heavy compilations ("kernel BUG at mm/zswap.c:1005!" and "Oops: invalid opcode: 0000")

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Message-ID: <ZtD2McWko3uobU-B@casper.infradead.org>
Date: Thu, 29 Aug 2024 23:29:05 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: Piotr Oniszczuk <piotr.oniszczuk@...il.com>,
	Pedro Falcato <pedro.falcato@...il.com>,
	Nhat Pham <nphamcs@...il.com>,
	Linux regressions mailing list <regressions@...ts.linux.dev>,
	LKML <linux-kernel@...r.kernel.org>,
	Johannes Weiner <hannes@...xchg.org>, Linux-MM <linux-mm@...ck.org>
Subject: Re: [regression] oops on heavy compilations ("kernel BUG at
 mm/zswap.c:1005!" and "Oops: invalid opcode: 0000")

On Thu, Aug 29, 2024 at 02:54:25PM -0700, Yosry Ahmed wrote:
> Looking at the zswap commits between 6.8 and 6.9, ignoring cleanups
> and seemingly irrelevant patches (e.g. swapoff fixups), I think the
> some likely candidates could be the following, but this is not really
> based on any scientific methodology:
> 
> 44c7c734a5132 mm/zswap: split zswap rb-tree
> c2e2ba770200b mm/zswap: only support zswap_exclusive_loads_enabled
> a230c20e63efe mm/zswap: zswap entry doesn't need refcount anymore
> 8409a385a6b41 mm/zswap: improve with alloc_workqueue() call
> 0827a1fb143fa mm/zswap: invalidate zswap entry when swap entry free
> 
> I also noticed that you are using z3fold as the zpool. Is the problem
> reproducible with zsmalloc? I wouldn't be surprised if there's a
> z3fold bug somewhere.

You're assuming that it's a zswap/zsmalloc/... bug.  If it's a random
scribble, as suggested by Takero Funaki:

https://lore.kernel.org/linux-mm/CAPpoddere2g=kkMzrxuJ1KCG=0Hg1-1v=ppg4dON9wK=pKq2uQ@mail.gmail.com/

then focusing on zswap will not be fruitful.