linux-kernel - Re: Linux6.14-rc5 BUG: spinlock bad magic in z3fold_zpool

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Message-ID: <CAKEwX=NqqsO6ajKffUFE1Y4B-YUhABudPbgAKy=16nN_k_-+fQ@mail.gmail.com>
Date: Thu, 27 Mar 2025 10:22:41 -0400
From: Nhat Pham <nphamcs@...il.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: ffhgfv <xnxc22xnxc22@...com>, "vitaly.wool" <vitaly.wool@...sulko.com>, 
	linmiaohe <linmiaohe@...wei.com>, akpm <akpm@...ux-foundation.org>, 
	linux-mm <linux-mm@...ck.org>, linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Linux6.14-rc5 BUG: spinlock bad magic in z3fold_zpool_free

On Wed, Mar 26, 2025 at 4:42 PM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Wed, Mar 26, 2025 at 03:43:28PM -0400, Nhat Pham wrote:
> > On Wed, Mar 26, 2025 at 10:32 AM Nhat Pham <nphamcs@...il.com> wrote:
> > > On Wed, Mar 26, 2025 at 10:11 AM ffhgfv <xnxc22xnxc22@...com> wrote:
> > > >
> > > > Hello, I found a bug titled " BUG: spinlock bad magic in z3fold_zpool_free   " with modified syzkaller in the Linux6.14-rc5.
> > > > If you fix this issue, please add the following tag to the commit:  Reported-by: Jianzhou Zhao <xnxc22xnxc22@...com>,    xingwei lee <xrivendell7@...il.com>, Zhizhuo Tang <strforexctzzchange@...mail.com>
> > >
> > > Please stop using z3fold :) We already removed it upstream.
> >
> > To clarify a little bit - we've found that z3fold is buggy (for a very
> > long time), and does not outperform zsmalloc in many of the workloads
> > we test on (both microbenchmark and real production workloads). We've
> > deprecated it since 6.12:
> >
> > https://github.com/torvalds/linux/commit/7a2369b74abf76cd3e54c45b30f6addb497f831b
> >
> > and will remove it altogether:
> >
> > https://lore.kernel.org/all/20250129180633.3501650-1-yosry.ahmed@linux.dev/
> >
> > Perhaps Vitaly can fix the issue for stability's sake (or in case
> > there is a reason why you MUST use z3fold)? But I strongly recommend
> > you experiment with zsmalloc :)
>
> This group are syzkaller kiddies.  They have no understanding of what
> they're testing; they're just running their fuzzer and sending emails.
> They don't care what's useful, so there's a lot of noise from unmaintained
> filesystems and so on.

You're right - I just realized they did it once already for zswap:

https://lore.kernel.org/all/tencent_49DA3E780998A9B96ADC9FF658CC84641808@qq.com/

It was also due to the (soon-to-be-removed) z3fold backend. To save
time, I'll stop engaging from now on, unless it's a proper issue.