linux-kernel - Re: [PATCH v7 06/21] mm/vma: Change munmap to use vma_munmap_struct() for accounting and surrounding vmas

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Message-ID: <fb6d107e-0e77-4c3a-be61-fdfb6e0c6cf0@lucifer.local>
Date: Fri, 23 Aug 2024 12:39:55 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Bert Karwatzki <spasswolf@....de>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Suren Baghdasaryan <surenb@...gle.com>,
        Matthew Wilcox <willy@...radead.org>, Vlastimil Babka <vbabka@...e.cz>,
        sidhartha.kumar@...cle.com, Jiri Olsa <olsajiri@...il.com>,
        Kees Cook <kees@...nel.org>, "Paul E . McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH v7 06/21] mm/vma: Change munmap to use
 vma_munmap_struct() for accounting and surrounding vmas

On Fri, Aug 23, 2024 at 12:42:18PM GMT, Bert Karwatzki wrote:
> Am Freitag, dem 23.08.2024 um 10:55 +0100 schrieb Lorenzo Stoakes:

[snip]

> > On Fri, Aug 23, 2024 at 10:43:11AM GMT, Bert Karwatzki wrote:
> >
> > [snip]
> > > I'm running the v7 Patchset on linux-next-20240822 and I get lots of these
> > > errors (right on boot) (both when using the complete patchset and when using
> > > only the patches up to this):
> >
> > Hm curious, I'm running this in qemu with CONFIG_DEBUG_VM set and don't see
> > this at lesat on next-20240823.
> >
> > Liam's series is based on the mseal series by Pedro, not sure if that wasn't in
> > 22 somehow?
> >
> > Can you try with 23, from tip and:
> >
> >     b4 shazam 20240822192543.3359552-1-Liam.Howlett@...cle.com
> >
> > To grab this series just to be sure?
> >
> > Because that'd definitely be very weird + concerning and something we hadn't
> > seen before (I don't think?) for the mm->data_vm to be incorrect...
> >
> > >

[snip]

>
> I grabbed the patches by saving the v7 patch emails as an mbox file and using
> git am to apply them (which worked without error) and git pull --rebase to
> update the series to next-20240823 (which works without conflicts).

Thanks, you are right, see other thread for an explanation. Good spot!

[snip - for brevity cutting dmesg logs, but much appreciated!]

These messages aside everything seems to work (I sending this email using the
> affected kernel) so I'm wondering if the checks aren't a little too paranoid.

Just to make the point - if these checks were the correct way around, this
would indicate that key mm counters are underflowing, which would be very
serious indeed - so just paranoid enough :) The paranoia is because this
should never happen.

>
> By the way: These 6 patches by Pedro Falcato are present in linux-next-20240822,
> too:
>
> mm: remove can_modify_mm()	Pedro Falcato
> mseal: replace can_modify_mm_madv with a vma variant	Pedro Falcato
> mm/mremap: replace can_modify_mm with can_modify_vma	Pedro Falcato
> mm/mprotect: replace can_modify_mm with can_modify_vma	Pedro Falcato
> mm/munmap: replace can_modify_mm with can_modify_vma	Pedro Falcato
> mm: move can_modify_vma to mm/vma.h			Pedro Falcato
>
> Bert Karwatzki
>

Thanks for confirming!