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

[Suren Baghdasaryan <surenb@google.com>]

On Sun, May 18, 2025 at 8:24 PM Hailong Liu <hailong.liu@oppo.com> wrote:
>
>
>
> On 5/9/2025 11:27 PM, Suren Baghdasaryan wrote:
> > On Wed, May 7, 2025 at 8:50 AM Liam R. Howlett <Liam.Howlett@oracle.com> wrote:
> >>
> >> * Liam R. Howlett <Liam.Howlett@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@unisoc.com>
> >>> Reported-by: Hailong Liu <hailong.liu@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@oracle.com>
> >>> Cc: Suren Baghdasaryan <surenb@google.com>
> >>> Cc: Hailong Liu <hailong.liu@oppo.com>
> >>> Cc: zhangpeng.00@bytedance.com <zhangpeng.00@bytedance.com>
> >>> Cc: Steve Kang <Steve.Kang@unisoc.com>
> >>> Cc: Matthew Wilcox <willy@infradead.org>
> >>> Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
> >>> Signed-off-by: Liam R. Howlett <Liam.Howlett@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
> >
> > 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.
> Sorry for late reply. We applied this patch and verified it fix the issue.
>
> Feel free to add
>
> Tested-by: Hailong Liu <hailong.liu@oppo.com>

Thanks! Once Liam posts the official fix I'll apply it to the Android
6.6 branch.

>
> Thanks,
> Hailong.
>
> > Thanks,
> > Suren.
> >
> >>
> >> Thanks,
> >> Liam
>