linux-kernel - Re: [ghes_copy_tofrom_phys] BUG: sleeping function called from invalid context at mm/page

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Date:   Mon, 30 Oct 2017 10:46:31 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Borislav Petkov <bp@...e.de>, Len Brown <lenb@...nel.org>,
        Tony Luck <tony.luck@...el.com>
Cc:     Fengguang Wu <fengguang.wu@...el.com>,
        Tyler Baicar <tbaicar@...eaurora.org>,
        Huang Ying <ying.huang@...el.com>,
        Chen Gong <gong.chen@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Will Deacon <will.deacon@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: [ghes_copy_tofrom_phys] BUG: sleeping function called from
 invalid context at mm/page_alloc.c:4150

On Mon, Oct 30, 2017 at 10:20 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> I will add a "might_sleep()" to ioremap_page_range() itself, so that
> we get this warning more reliably and much eailer. Right now it has
> been hidden by the fact that most of the time the time the page tables
> may be already allocated, but even then it's broken.

Done. It doesn't report anything for me, so _hopefully_ the GHES
driver is the only one that does games like this. See commit
b39ab98e2f47 ("Mark 'ioremap_page_range()' as possibly sleeping").

So now it should hopefully warn about this bad usage of page remapping
reliably, at least if you have CONFIG_DEBUG_ATOMIC_SLEEP enabled.

Can somebody who has a working GHES setup (although Borislav seems to
think no such thing exists) verify?

This obviously won't _fix_ anything, but at least it should make it
clear it's not that recent change that broke things - that just
happened to expose it. And hopefully somebody who knows that driver
will do the proper fixmap thing (or just ioremap once at probe time,
rather than at run-time).

                    Linus