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

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Date:   Wed, 8 Nov 2017 00:07:35 +0800
From:   Fengguang Wu <fengguang.wu@...el.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
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 07, 2017 at 07:51:00AM -0800, Linus Torvalds wrote:
>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.

I'll try disabling CONFIG_OPTIMIZE_FOR_SIZE for gcc 4.x.

Thanks,
Fengguang