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Revision aeb309b81c6bada783c3695528a3e10748e97285 authored by Huang Ying on 12 July 2019, 03:55:44 UTC, committed by Linus Torvalds on 12 July 2019, 18:05:43 UTC 
mm/mincore.c: fix race between swapoff and mincore
 
Via commit 4b3ef9daa4fc ("mm/swap: split swap cache into 64MB trunks"),
after swapoff, the address_space associated with the swap device will be
freed.  So swap_address_space() users which touch the address_space need
some kind of mechanism to prevent the address_space from being freed
during accessing.

When mincore processes an unmapped range for swapped shmem pages, it
doesn't hold the lock to prevent swap device from being swapped off.  So
the following race is possible:

CPU1					CPU2
do_mincore()				swapoff()
  walk_page_range()
    mincore_unmapped_range()
      __mincore_unmapped_range
        mincore_page
	  as = swap_address_space()
          ...				  exit_swap_address_space()
          ...				    kvfree(spaces)
	  find_get_page(as)

The address space may be accessed after being freed.

To fix the race, get_swap_device()/put_swap_device() is used to enclose
find_get_page() to check whether the swap entry is valid and prevent the
swap device from being swapoff during accessing.

Link: http://lkml.kernel.org/r/20190611020510.28251-1-ying.huang@intel.com
Fixes: 4b3ef9daa4fc ("mm/swap: split swap cache into 64MB trunks")
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Raw File
gcc-plugins.txt 
=========================
GCC plugin infrastructure
=========================


Introduction
============

GCC plugins are loadable modules that provide extra features to the
compiler [1]_. They are useful for runtime instrumentation and static analysis.
We can analyse, change and add further code during compilation via
callbacks [2]_, GIMPLE [3]_, IPA [4]_ and RTL passes [5]_.

The GCC plugin infrastructure of the kernel supports all gcc versions from
4.5 to 6.0, building out-of-tree modules, cross-compilation and building in a
separate directory.
Plugin source files have to be compilable by both a C and a C++ compiler as well
because gcc versions 4.5 and 4.6 are compiled by a C compiler,
gcc-4.7 can be compiled by a C or a C++ compiler,
and versions 4.8+ can only be compiled by a C++ compiler.

Currently the GCC plugin infrastructure supports only the x86, arm, arm64 and
powerpc architectures.

This infrastructure was ported from grsecurity [6]_ and PaX [7]_.

--

.. [1] https://gcc.gnu.org/onlinedocs/gccint/Plugins.html
.. [2] https://gcc.gnu.org/onlinedocs/gccint/Plugin-API.html#Plugin-API
.. [3] https://gcc.gnu.org/onlinedocs/gccint/GIMPLE.html
.. [4] https://gcc.gnu.org/onlinedocs/gccint/IPA.html
.. [5] https://gcc.gnu.org/onlinedocs/gccint/RTL.html
.. [6] https://grsecurity.net/
.. [7] https://pax.grsecurity.net/


Files
=====

**$(src)/scripts/gcc-plugins**

	This is the directory of the GCC plugins.

**$(src)/scripts/gcc-plugins/gcc-common.h**

	This is a compatibility header for GCC plugins.
	It should be always included instead of individual gcc headers.

**$(src)/scripts/gcc-plugin.sh**

	This script checks the availability of the included headers in
	gcc-common.h and chooses the proper host compiler to build the plugins
	(gcc-4.7 can be built by either gcc or g++).

**$(src)/scripts/gcc-plugins/gcc-generate-gimple-pass.h,
$(src)/scripts/gcc-plugins/gcc-generate-ipa-pass.h,
$(src)/scripts/gcc-plugins/gcc-generate-simple_ipa-pass.h,
$(src)/scripts/gcc-plugins/gcc-generate-rtl-pass.h**

	These headers automatically generate the registration structures for
	GIMPLE, SIMPLE_IPA, IPA and RTL passes. They support all gcc versions
	from 4.5 to 6.0.
	They should be preferred to creating the structures by hand.


Usage
=====

You must install the gcc plugin headers for your gcc version,
e.g., on Ubuntu for gcc-4.9::

	apt-get install gcc-4.9-plugin-dev

Enable a GCC plugin based feature in the kernel config::

	CONFIG_GCC_PLUGIN_CYC_COMPLEXITY = y

To compile only the plugin(s)::

	make gcc-plugins

or just run the kernel make and compile the whole kernel with
the cyclomatic complexity GCC plugin.


4. How to add a new GCC plugin
==============================

The GCC plugins are in $(src)/scripts/gcc-plugins/. You can use a file or a directory
here. It must be added to $(src)/scripts/gcc-plugins/Makefile,
$(src)/scripts/Makefile.gcc-plugins and $(src)/arch/Kconfig.
See the cyc_complexity_plugin.c (CONFIG_GCC_PLUGIN_CYC_COMPLEXITY) GCC plugin.
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