linux-kernel - Re: [PATCH v8 1/4] fs/proc/kcore: avoid bounce buffer for ktext data

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Message-ID: <27ad89fe-1b69-4d62-916f-d494b32c8ddf@lucifer.local>
Date:   Mon, 31 Jul 2023 22:58:09 +0100
From:   Lorenzo Stoakes <lstoakes@...il.com>
To:     Jiri Olsa <olsajiri@...il.com>
Cc:     David Hildenbrand <david@...hat.com>, Baoquan He <bhe@...hat.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Liu Shixin <liushixin2@...wei.com>,
        Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v8 1/4] fs/proc/kcore: avoid bounce buffer for ktext data

On Mon, Jul 31, 2023 at 11:50:22PM +0200, Jiri Olsa wrote:
> > Ummmm what? I can't! What repro are you seeing on x86, exactly?
>
> # cat /proc/kallsyms | grep ksys_read
> ffffffff8151e450 T ksys_read
>
> # objdump -d  --start-address=0xffffffff8151e450 --stop-address=0xffffffff8151e460 /proc/kcore
>
> /proc/kcore:     file format elf64-x86-64
>
> objdump: Reading section load1 failed because: Bad address
>
>
> jirka

Locally I don't see this issue. How odd. The bug doesn't manifest as a 'bad
address' in the arm64 repros either. I wonder if this is something unrelated...

In any case I have a candidate fix for the bug at
https://lore.kernel.org/all/20230731215021.70911-1-lstoakes@gmail.com/ which
should hopefully address the underlying issue with minimum change.