linux-kernel - uninitialized pmem struct pages

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Message-ID: <20210104100323.GC13207@dhcp22.suse.cz>
Date:   Mon, 4 Jan 2021 11:03:23 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: uninitialized pmem struct pages

Hi,
back in March [1] you have recommended 53cdc1cb29e8
("drivers/base/memory.c: indicate all memory blocks as removable") to be
backported to stable trees and that has led to a more general discussion
about the current state of pfn walkers wrt. uninitialized pmem struct
pages. We haven't concluded any specific solution for that except for a
general sentiment that pfn_to_online_page should be able to catch those.
I might have missed any follow ups on that but I do not think we have
landed on any actual solution in the end. Have I just missed any followups?

Is anybody working on that?

Also is there any reference explaining what those struct pages are and
why we cannot initialize them? I am sorry if this has been explained to
me but I really cannot find that in my notes anywhere. Most pmem pages
should be initialized via memmap_init_zone_device, right?

I am asking mostly because we are starting to see these issues in
production and while the only visible problem so far is a crash when
reading sysfs (removable file) I am worried we are just lucky no other
pfn walker stumble over this.

[1] http://lkml.kernel.org/r/CAPcyv4jpdaNvJ67SkjyUJLBnBnXXQv686BiVW042g03FUmWLXw@mail.gmail.com
-- 
Michal Hocko
SUSE Labs