lkml.org 
[lkml]   [2017]   [Aug]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] mm: allow page_cache_get_speculative in interrupt context
On Tue,  1 Aug 2017 13:39:06 -0400 kan.liang@intel.com wrote:

> Kernel panic when calling the IRQ-safe __get_user_pages_fast in NMI
> handler.
>
> The bug was introduced by commit:
>
> 2947ba054a4d ("x86/mm/gup: Switch GUP to the generic
> get_user_page_fast() implementation")
>
> The original x86 __get_user_page_fast used plain get_page() or
> page_ref_add(). However, the generic __get_user_page_fast uses
> page_cache_get_speculative(), which has VM_BUG_ON(in_interrupt()).
>
> There is no reason to prevent page_cache_get_speculative from using in
> interrupt context. According to the author, putting a BUG_ON there is
> just because the code is not verifying correctness of interrupt races.
> I did some tests in interrupt context. There is no issue found.
> Removing VM_BUG_ON(in_interrupt()) for page_cache_get_speculative().

What code calls page_cache_get_speculative() from NMI context?

I'm trying to work out which kernel versions need this fix, but there
isn't enough info in the changelog for this. Please don't do that.

\
 
 \ /
  Last update: 2017-08-01 21:50    [W:0.037 / U:2.764 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site