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

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Message-ID: <CAKPOu+9MLQ5rH-eQ6SuiXTzFCEhmaZ9s-nKKQ4vpUCyvc9ho8g@mail.gmail.com>
Date: Fri, 5 Sep 2025 05:41:38 +0200
From: Max Kellermann <max.kellermann@...os.com>
To: Viacheslav Dubeyko <Slava.Dubeyko@....com>
Cc: Xiubo Li <xiubli@...hat.com>, Alex Markuze <amarkuze@...hat.com>, 
	"idryomov@...il.com" <idryomov@...il.com>, "stable@...r.kernel.org" <stable@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>
Subject: Re: [PATCH] fs/ceph/addr: always call ceph_shift_unused_folios_left()

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.