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

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Message-ID: <z2hyuganxadlf7guskolgd6epu75jutipt7uwg5sqwew6a7lyv@6fbcue5r745x>
Date: Wed, 7 May 2025 11:50:36 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: 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()

* 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?

Thanks,
Liam