linux-kernel - RE: [PATCH] fs/ceph/addr: always call ceph_shift_unused_folios

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Message-ID: <b3d2da1abe05087f52a8e770bd8eac04c46b3370.camel@ibm.com>
Date: Fri, 5 Sep 2025 17:11:54 +0000
From: Viacheslav Dubeyko <Slava.Dubeyko@....com>
To: "max.kellermann@...os.com" <max.kellermann@...os.com>
CC: "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>,
        Xiubo Li
	<xiubli@...hat.com>, Alex Markuze <amarkuze@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "idryomov@...il.com" <idryomov@...il.com>
Subject: RE: [PATCH] fs/ceph/addr: always call ceph_shift_unused_folios_left()

On Fri, 2025-09-05 at 05:41 +0200, Max Kellermann wrote:
> On Thu, Sep 4, 2025 at 11:43 PM Viacheslav Dubeyko
> <Slava.Dubeyko@....com> wrote:
> > By applying the patch [1], enabling CONFIG_DEBUG_VM, and returning -E2BIG from
> > ceph_check_page_before_write(), I was able to reproduce this warning:
> 
> Thanks, I'm glad you could verify the bug and my fix. In case this
> wasn't clear: you saw just a warning, but this is usually a kernel
> crash due to NULL pointer dereference. If you only got a warning but
> no crash, it means your test VM does not use transparent huge pages
> (no huge_zero_folio allocated yet). In a real workload, the kernel
> would have crashed.

I would like to reproduce the crash. But you've share only these steps.
And it looks like that it's not the complete recipe. So, something was missing.
If you could share more precise explanation of steps, it will be great.

Thanks,
Slava.