linux-kernel - Re: [RFC PATCH v6.6] maple_tree: Fix MA_STATE_PREALLOC flag in mas

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Message-ID: <CAJuCfpFXuyg+otnr2uHauGi1-UD2sxxS26ONQNBwuUUisOssQQ@mail.gmail.com>
Date: Fri, 9 May 2025 08:27:23 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>, maple-tree@...ts.infradead.org, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	Zhaoyang Huang <zhaoyang.huang@...soc.com>, Hailong Liu <hailong.liu@...o.com>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Suren Baghdasaryan <surenb@...gle.com>, 
	"zhangpeng . 00 @ bytedance . com" <zhangpeng.00@...edance.com>, Steve Kang <Steve.Kang@...soc.com>, 
	Matthew Wilcox <willy@...radead.org>, Sidhartha Kumar <sidhartha.kumar@...cle.com>
Subject: Re: [RFC PATCH v6.6] maple_tree: Fix MA_STATE_PREALLOC flag in mas_preallocate()

On Wed, May 7, 2025 at 8:50 AM Liam R. Howlett <Liam.Howlett@...cle.com> wrote:
>
> * Liam R. Howlett <Liam.Howlett@...cle.com> [250428 21:48]:
> > Temporarily clear the preallocation flag when explicitly requesting
> > allocations.  Pre-existing allocations are already counted against the
> > request through mas_node_count_gfp(), but the allocations will not
> > happen if the MA_STATE_PREALLOC flag is set.  This flag is meant to
> > avoid re-allocating in bulk allocation mode, and to detect issues with
> > preallocation calculations.
> >
> > The MA_STATE_PREALLOC flag should also always be set on zero allocations
> > so that detection of underflow allocations will print a WARN_ON() during
> > consumption.
> >
> > User visible effect of this flaw is a WARN_ON() followed by a null
> > pointer dereference when subsequent requests for larger number of nodes
> > is ignored, such as the vma merge retry in mmap_region() caused by
> > drivers altering the vma flags.
> >
> > Reported-by: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> > Reported-by: Hailong Liu <hailong.liu@...o.com>
> > Fixes: 54a611b605901 ("Maple Tree: add new data structure")
> > Link: https://lore.kernel.org/all/1652f7eb-a51b-4fee-8058-c73af63bacd1@oppo.com/
> > Link: https://lore.kernel.org/all/20250428184058.1416274-1-Liam.Howlett@oracle.com/
> > Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> > Cc: Suren Baghdasaryan <surenb@...gle.com>
> > Cc: Hailong Liu <hailong.liu@...o.com>
> > Cc: zhangpeng.00@...edance.com <zhangpeng.00@...edance.com>
> > Cc: Steve Kang <Steve.Kang@...soc.com>
> > Cc: Matthew Wilcox <willy@...radead.org>
> > Cc: Sidhartha Kumar <sidhartha.kumar@...cle.com>
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
>
> ...
>
> I have a version of this for mm-new and I'd like to send it out.  Once
> this is upstream, it will be backported to the stable kernels with
> something that looks a lot like what I sent out here.
>
> Did this fix the issue in the longer running tests?

- everyone else

Hi Liam,
I think the delay is due to the holidays in China. I requested an
update from the partners but they will probably provide it next week.
Thanks,
Suren.

>
> Thanks,
> Liam