linux-kernel - /proc/*/maps broken on nommu

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Message-ID: <CAMo8BfLb6U9xtMtt1t9vQX_nKek7kEt+Rvv5NwpvTHu0kdiXcg@mail.gmail.com>
Date:   Sun, 17 Sep 2023 04:38:07 -0700
From:   Max Filippov <jcmvbkbc@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>
Cc:     Matthew Wilcox <willy@...radead.org>, Yu Zhao <yuzhao@...gle.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Davidlohr Bueso <dave@...olabs.net>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: /proc/*/maps broken on nommu

Hello,

As of v6.5 cat /proc/*/maps produces empty output on nommu xtensa systems.
Bisection points to the commit 0c563f148043 ("proc: remove VMA rbtree
use from nommu").
It looks like the issue may be not in the m_start (where find_vma(mm,
addr) returns
NULL), but in the nommu version of find_vma itself. I've tried replacing nommu
find_vma implementation with an implementation of the MMU version and it
fixes the /proc/*/maps output. Kind of (it works as expected on one of
my systems,
but consistently locks up on the other).

Any suggestions of what might be wrong/how to fix it properly?

-- 
Thanks.
-- Max