linux-kernel - Re: linux-next boot error: WARNING in kmem_cache

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Message-ID: <CACT4Y+ZcbA=9L2XPC_rRG-FdwOoH6XteOoGHg7jfvd+1CH2M+w@mail.gmail.com>
Date:   Mon, 22 Jun 2020 08:42:13 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Qian Cai <cai@....pw>
Cc:     syzbot <syzbot+95bccd805a4aa06a4b0d@...kaller.appspotmail.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: linux-next boot error: WARNING in kmem_cache_free

On Mon, Jun 22, 2020 at 8:29 AM Qian Cai <cai@....pw> wrote:
> > On Jun 22, 2020, at 1:37 AM, syzbot <syzbot+95bccd805a4aa06a4b0d@...kaller.appspotmail.com> wrote:
> >
> > WARNING: CPU: 0 PID: 0 at mm/slab.h:232 kmem_cache_free+0x0/0x200 mm/slab.c:2262
>
> Is there any particular reason to use CONFIG_SLAB rather than CONFIG_SLUB?

There is a reason, it's still important for us.
But also it's not our strategy to deal with bugs by not testing
configurations and closing eyes on bugs, right? If it's an official
config in the kernel, it needs to be tested. If SLAB is in the state
that we don't care about any bugs in it, then we need to drop it. It
will automatically remove it from all testing systems out there. Or at
least make it "depends on BROKEN" to slowly phase it out during
several releases.


> You are really asking for trouble to test something that almost nobody is exercising that code path very well nowadays.
>
> Anyway, there is a patchset in -mm that might well introduce this regression that we could go to confirm it, but I kind of don’t want to spend too much time on SLAB that suppose to be obsolete eventually.