linux-kernel - Re: [PATCH 0/8] Fix VMA tree modification under mmap read lock

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Date:   Mon, 3 Apr 2023 15:44:43 -0400
From:   "Liam R. Howlett" <Liam.Howlett@...cle.com>
To:     Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        maple-tree@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Matthew Wilcox <willy@...radead.org>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH 0/8] Fix VMA tree modification under mmap read lock

* Liam R. Howlett <Liam.Howlett@...cle.com> [230328 09:02]:
> * Vlastimil Babka <vbabka@...e.cz> [230328 05:11]:
> > On 3/27/23 21:48, Liam R. Howlett wrote:
> > > * Andrew Morton <akpm@...ux-foundation.org> [230327 15:35]:
> > >> On Mon, 27 Mar 2023 14:55:24 -0400 "Liam R. Howlett" <Liam.Howlett@...cle.com> wrote:
> > >> 
> > >> > These patches have been in -next since next-20230301, and have received
> > >> > intensive testing in Android as part of the RCU page fault patchset.
> > >> > They were also sent as part of the "Per-VMA locks" v4 patch series.
> > >> > Patches 1 to 7 are bug fixes for RCU mode of the tree and patch 8 enables
> > >> > RCU mode for the tree.
> > >> 
> > >> What's happening here?  I assume you've decided that the first 8
> > >> patches of the "Per-VMA locks v4" series should be fast-tracked into
> > >> 6.3-rcX and backported?  And we retain the rest of that series for
> > >> 6.4-rc1?
> > > 
> > > Yes, they need to be backported and fast tracked to fix the issue syzbot
> > > found.
> > 
> > Stable usually wants the "mainline first" which means fast tracking first,
> > then once it's in mainline, they pick it and annotate with mainline commit id.
> 
> Right.  I meant these patches won't cleanly apply to 6.1/6.2 and will
> need more than just a cherry-pick due to the vma iterator changes.  I
> have those modified patches ready to go as well.
> 
> > 
> > One question is how Linus would feel about this now for rc5.
> > 
> > Another question is if we should really deviate in the patch 8/8 backport
> > just because it's not necessary for stable. Generally they would also prefer
> > not to deviate, unless there's a strong reason.
> 
> Just to clarify, the change is to remove something that isn't necessary
> at all.
> 

Andrew,

I just wanted to know where we stand with these patches?

I understand that it's late in the cycle, but this is a bug that affects
6.1, 6.2, 6.3-rc5 and can be triggered from userspace.

I'm asking because the LTS 6.1 is starting to be picked up by
distributions, although I don't know the scale of the install, and
getting these upstream will allow for the backported fixes to be picked
up by stable quicker.

Thanks,
Liam