Re: [linux-next:master] [maple_tree] 540335e987: BUG:kernel_NULL_pointer_dereference,address

[Wei Yang <richard.weiyang@gmail.com>]

On Mon, Jun 23, 2025 at 05:19:07PM -0400, Liam R. Howlett wrote:
[...]
>
>This will need to be addressed once the dense nodes arrive, but it
>really should not happen right now.
>
>I don't like the idea of checking this every time we walk a node, if it
>can be avoided.
>
>> 
>> Sorry for the trouble. It is better to drop it.
>
>This indicates another issue exists which was exposed with your fix.
>
>I've tracked it down to the maple status being restored to ma_active
>before the maple state node is set.  The bot looks to have hit this by
>going mas_prev() on 0 and getting the status to ma_underflow, then
>mas_find(), which restored it to ma_active and tried to walk when the
>node was NULL in mas_find_setup().
>

The analysis looks reasonable. Thanks for your time.

>I have a fix for this and I'll roll your change into my fix and add you
>as the reporter... and add links to the resend, v3 patches, and this
>thread.  Stable will be excluded because it's really not worth the risk
>- the code is stable now but just suboptimal.
>
>This still leaves your initial patch 1 and 3, which has nothing to do
>with either of these bugs that you included in the patch set.  It is
>best to keep patches related to each other together, but not include
>things you find while developing those fixes, specifically for this
>scenario.
>
>I will grab those patches and re-examine them before sending them along,
>again.
>
>Thanks,
>Liam

-- 
Wei Yang
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