[RFC PATCH v6.6] maple_tree: Fix MA_STATE_PREALLOC flag in mas_preallocate()

[Suren Baghdasaryan]

On Fri, May 9, 2025 at 8:27 AM Suren Baghdasaryan <surenb at google.com> wrote:
>
> On Wed, May 7, 2025 at 8:50 AM Liam R. Howlett <Liam.Howlett at oracle.com> wrote:
> >
> > * Liam R. Howlett <Liam.Howlett at oracle.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 at unisoc.com>
> > > Reported-by: Hailong Liu <hailong.liu at oppo.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 at oracle.com>
> > > Cc: Suren Baghdasaryan <surenb at google.com>
> > > Cc: Hailong Liu <hailong.liu at oppo.com>
> > > Cc: zhangpeng.00 at bytedance.com <zhangpeng.00 at bytedance.com>
> > > Cc: Steve Kang <Steve.Kang at unisoc.com>
> > > Cc: Matthew Wilcox <willy at infradead.org>
> > > Cc: Sidhartha Kumar <sidhartha.kumar at oracle.com>
> > > Signed-off-by: Liam R. Howlett <Liam.Howlett at oracle.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

and of course I forgot to remove everyone else :) Sorry for the spam.

>
> 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