linux-ext4 - Re: Potential regression on kernel 5.19-rc0: kernel BUG at mm/page_table

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Date:   Tue, 31 May 2022 02:39:08 +0800
From:   Zorro Lang <zlang@...hat.com>
To:     linux-mm@...ck.org
Cc:     linux-xfs@...r.kernel.org, linux-ext4@...r.kernel.org,
        nvdimm@...ts.linux.dev
Subject: Re: Potential regression on kernel 5.19-rc0: kernel BUG at
 mm/page_table_check.c:51!

On Mon, May 30, 2022 at 04:06:16PM +0800, Zorro Lang wrote:
> Hi mm folks:
> 
> I reported a regression bug on latest upstream linux:
> https://bugzilla.kernel.org/show_bug.cgi?id=216047
> 
> It's about xfs/ext4 + DAX, panic at mm/page_table_check.c:51!
> 
>   static struct page_table_check *get_page_table_check(struct page_ext *page_ext)
>   {
> ==>     BUG_ON(!page_ext);
>         return (void *)(page_ext) + page_table_check_ops.offset;
>   }
> 
> It's 100% reproducible for me, by running fstests generic/623:
>   https://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git/tree/tests/generic/623
> on xfs or ext4 with DAX enabled.
> 
> It doesn't look like a xfs or ext4 issue, so send to linux-mm to get more
> reviewing. More details please refer to above bug link. I changed its Pruduct
> to mm, but the Assignee isn't changed by default.

It's not a regression *recently* at least, I still can reproduce this bug on
linux v5.16.

But I found it's related with someone kernel configuration (sorry I haven't
figured out which one config is). I've upload two kernel config files, one[1]
can build a kernel which reproduce this bug, the other[2] can't. Hope that
helps.

Thanks,
Zorro

[1]
https://bugzilla.kernel.org/attachment.cgi?id=301076

[2]
https://bugzilla.kernel.org/attachment.cgi?id=301077

> 
> Thanks,
> Zorro