linux-kernel - Re: [inotify_read] BUG: unable to handle kernel paging request at ffff8800172f8000

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Message-ID: <CA+55aFybLHpR0KVo-nXjBgXD6B5vnNryVg19y--wSU-0CbVrTQ@mail.gmail.com>
Date:   Tue, 7 Nov 2017 07:51:00 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Fengguang Wu <fengguang.wu@...el.com>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Jan Kara <jack@...e.cz>, Amir Goldstein <amir73il@...il.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Nikolay Borisov <n.borisov.lkml@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [inotify_read] BUG: unable to handle kernel paging request at ffff8800172f8000

On Tue, Nov 7, 2017 at 2:28 AM, Fengguang Wu <fengguang.wu@...el.com> wrote:
> FYI This bug trace also contains inotify_read().
>
> [    3.365745] BUG: unable to handle kernel paging request at ffff8800172f8000
> [    3.366661] IP: slob_free+0x1c4/0x276
> [    3.373500] RBP: ffff8800172f7ffe

Same gcc bug: it's a 2-byte read from the end of the page that has
been turned by gcc into a 4-byte read, and causes an oops because your
gcc version is bad.

I *think* it's triggered by CONFIG_OPTIMIZE_FOR_SIZE=y, which causes
gcc to generate garbage code. Yes, the 32-bit read is one byte shorter
because it doesn't have a operand size prefix, but it's buggy.

               Linus