linux-kernel - Re: [x86/mm/gup] 2947ba054a [ 71.329069] kernel BUG at include/linux/pagemap.h:151!

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Date:   Fri, 24 Mar 2017 11:51:53 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Fengguang Wu <fengguang.wu@...el.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, LKP <lkp@...org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [x86/mm/gup] 2947ba054a [   71.329069] kernel BUG at
 include/linux/pagemap.h:151!

On Fri, Mar 24, 2017 at 01:24:36PM +0300, Kirill A. Shutemov wrote:

> I'm not sure what is the best way to fix this.
> Few options:
>  - Drop the VM_BUG();
>  - Bump preempt count during __get_user_pages_fast();
>  - Use get_page() instead of page_cache_get_speculative() on x86.
> 
> Any opinions?

I think I'm in favour of the first; either remove or amend to include
irqs_disabled() or so.

This in favour of keeping the variants of GUP down.