1. 27 7月, 2015 1 次提交
  2. 10 5月, 2015 1 次提交
  3. 13 4月, 2015 2 次提交
  4. 12 4月, 2015 1 次提交
  5. 10 3月, 2015 1 次提交
  6. 13 2月, 2015 1 次提交
    • A
      all arches, signal: move restart_block to struct task_struct · f56141e3
      Andy Lutomirski 提交于
      If an attacker can cause a controlled kernel stack overflow, overwriting
      the restart block is a very juicy exploit target.  This is because the
      restart_block is held in the same memory allocation as the kernel stack.
      
      Moving the restart block to struct task_struct prevents this exploit by
      making the restart_block harder to locate.
      
      Note that there are other fields in thread_info that are also easy
      targets, at least on some architectures.
      
      It's also a decent simplification, since the restart code is more or less
      identical on all architectures.
      
      [james.hogan@imgtec.com: metag: align thread_info::supervisor_stack]
      Signed-off-by: NAndy Lutomirski <luto@amacapital.net>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Al Viro <viro@zeniv.linux.org.uk>
      Cc: "H. Peter Anvin" <hpa@zytor.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Kees Cook <keescook@chromium.org>
      Cc: David Miller <davem@davemloft.net>
      Acked-by: NRichard Weinberger <richard@nod.at>
      Cc: Richard Henderson <rth@twiddle.net>
      Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
      Cc: Matt Turner <mattst88@gmail.com>
      Cc: Vineet Gupta <vgupta@synopsys.com>
      Cc: Russell King <rmk@arm.linux.org.uk>
      Cc: Catalin Marinas <catalin.marinas@arm.com>
      Cc: Will Deacon <will.deacon@arm.com>
      Cc: Haavard Skinnemoen <hskinnemoen@gmail.com>
      Cc: Hans-Christian Egtvedt <egtvedt@samfundet.no>
      Cc: Steven Miao <realmz6@gmail.com>
      Cc: Mark Salter <msalter@redhat.com>
      Cc: Aurelien Jacquiot <a-jacquiot@ti.com>
      Cc: Mikael Starvik <starvik@axis.com>
      Cc: Jesper Nilsson <jesper.nilsson@axis.com>
      Cc: David Howells <dhowells@redhat.com>
      Cc: Richard Kuo <rkuo@codeaurora.org>
      Cc: "Luck, Tony" <tony.luck@intel.com>
      Cc: Geert Uytterhoeven <geert@linux-m68k.org>
      Cc: Michal Simek <monstr@monstr.eu>
      Cc: Ralf Baechle <ralf@linux-mips.org>
      Cc: Jonas Bonn <jonas@southpole.se>
      Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
      Cc: Helge Deller <deller@gmx.de>
      Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
      Cc: Paul Mackerras <paulus@samba.org>
      Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
      Tested-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
      Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
      Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
      Cc: Chen Liqin <liqin.linux@gmail.com>
      Cc: Lennox Wu <lennox.wu@gmail.com>
      Cc: Chris Metcalf <cmetcalf@ezchip.com>
      Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
      Cc: Chris Zankel <chris@zankel.net>
      Cc: Max Filippov <jcmvbkbc@gmail.com>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Guenter Roeck <linux@roeck-us.net>
      Signed-off-by: NJames Hogan <james.hogan@imgtec.com>
      Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      f56141e3
  7. 10 10月, 2014 1 次提交
  8. 06 8月, 2014 2 次提交
  9. 14 11月, 2013 1 次提交
  10. 15 7月, 2013 1 次提交
    • P
      m32r: delete __cpuinit usage from all m32r files · d1407fde
      Paul Gortmaker 提交于
      The __cpuinit type of throwaway sections might have made sense
      some time ago when RAM was more constrained, but now the savings
      do not offset the cost and complications.  For example, the fix in
      commit 5e427ec2 ("x86: Fix bit corruption at CPU resume time")
      is a good example of the nasty type of bugs that can be created
      with improper use of the various __init prefixes.
      
      After a discussion on LKML[1] it was decided that cpuinit should go
      the way of devinit and be phased out.  Once all the users are gone,
      we can then finally remove the macros themselves from linux/init.h.
      
      Note that some harmless section mismatch warnings may result, since
      notify_cpu_starting() and cpu_up() are arch independent (kernel/cpu.c)
      are flagged as __cpuinit  -- so if we remove the __cpuinit from
      arch specific callers, we will also get section mismatch warnings.
      As an intermediate step, we intend to turn the linux/init.h cpuinit
      content into no-ops as early as possible, since that will get rid
      of these warnings.  In any case, they are temporary and harmless.
      
      This removes all the arch/m32r uses of the __cpuinit macros from
      all C files.  Currently m32r does not have any __CPUINIT used in
      assembly files.
      
      [1] https://lkml.org/lkml/2013/5/20/589
      
      Cc: Hirokazu Takata <takata@linux-m32r.org>
      Cc: linux-m32r@ml.linux-m32r.org
      Cc: linux-m32r-ja@ml.linux-m32r.org
      Signed-off-by: NPaul Gortmaker <paul.gortmaker@windriver.com>
      d1407fde
  11. 01 5月, 2013 2 次提交
    • T
      dump_stack: unify debug information printed by show_regs() · a43cb95d
      Tejun Heo 提交于
      show_regs() is inherently arch-dependent but it does make sense to print
      generic debug information and some archs already do albeit in slightly
      different forms.  This patch introduces a generic function to print debug
      information from show_regs() so that different archs print out the same
      information and it's much easier to modify what's printed.
      
      show_regs_print_info() prints out the same debug info as dump_stack()
      does plus task and thread_info pointers.
      
      * Archs which didn't print debug info now do.
      
        alpha, arc, blackfin, c6x, cris, frv, h8300, hexagon, ia64, m32r,
        metag, microblaze, mn10300, openrisc, parisc, score, sh64, sparc,
        um, xtensa
      
      * Already prints debug info.  Replaced with show_regs_print_info().
        The printed information is superset of what used to be there.
      
        arm, arm64, avr32, mips, powerpc, sh32, tile, unicore32, x86
      
      * s390 is special in that it used to print arch-specific information
        along with generic debug info.  Heiko and Martin think that the
        arch-specific extra isn't worth keeping s390 specfic implementation.
        Converted to use the generic version.
      
      Note that now all archs print the debug info before actual register
      dumps.
      
      An example BUG() dump follows.
      
       kernel BUG at /work/os/work/kernel/workqueue.c:4841!
       invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
       Modules linked in:
       CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.9.0-rc1-work+ #7
       Hardware name: empty empty/S3992, BIOS 080011  10/26/2007
       task: ffff88007c85e040 ti: ffff88007c860000 task.ti: ffff88007c860000
       RIP: 0010:[<ffffffff8234a07e>]  [<ffffffff8234a07e>] init_workqueues+0x4/0x6
       RSP: 0000:ffff88007c861ec8  EFLAGS: 00010246
       RAX: ffff88007c861fd8 RBX: ffffffff824466a8 RCX: 0000000000000001
       RDX: 0000000000000046 RSI: 0000000000000001 RDI: ffffffff8234a07a
       RBP: ffff88007c861ec8 R08: 0000000000000000 R09: 0000000000000000
       R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff8234a07a
       R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
       FS:  0000000000000000(0000) GS:ffff88007dc00000(0000) knlGS:0000000000000000
       CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
       CR2: ffff88015f7ff000 CR3: 00000000021f1000 CR4: 00000000000007f0
       DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
       DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
       Stack:
        ffff88007c861ef8 ffffffff81000312 ffffffff824466a8 ffff88007c85e650
        0000000000000003 0000000000000000 ffff88007c861f38 ffffffff82335e5d
        ffff88007c862080 ffffffff8223d8c0 ffff88007c862080 ffffffff81c47760
       Call Trace:
        [<ffffffff81000312>] do_one_initcall+0x122/0x170
        [<ffffffff82335e5d>] kernel_init_freeable+0x9b/0x1c8
        [<ffffffff81c47760>] ? rest_init+0x140/0x140
        [<ffffffff81c4776e>] kernel_init+0xe/0xf0
        [<ffffffff81c6be9c>] ret_from_fork+0x7c/0xb0
        [<ffffffff81c47760>] ? rest_init+0x140/0x140
        ...
      
      v2: Typo fix in x86-32.
      
      v3: CPU number dropped from show_regs_print_info() as
          dump_stack_print_info() has been updated to print it.  s390
          specific implementation dropped as requested by s390 maintainers.
      Signed-off-by: NTejun Heo <tj@kernel.org>
      Acked-by: NDavid S. Miller <davem@davemloft.net>
      Acked-by: NJesper Nilsson <jesper.nilsson@axis.com>
      Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
      Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
      Cc: Bjorn Helgaas <bhelgaas@google.com>
      Cc: Fengguang Wu <fengguang.wu@intel.com>
      Cc: Mike Frysinger <vapier@gentoo.org>
      Cc: Vineet Gupta <vgupta@synopsys.com>
      Cc: Sam Ravnborg <sam@ravnborg.org>
      Acked-by: Chris Metcalf <cmetcalf@tilera.com>		[tile bits]
      Acked-by: Richard Kuo <rkuo@codeaurora.org>		[hexagon bits]
      Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      a43cb95d
    • T
      dump_stack: consolidate dump_stack() implementations and unify their behaviors · 196779b9
      Tejun Heo 提交于
      Both dump_stack() and show_stack() are currently implemented by each
      architecture.  show_stack(NULL, NULL) dumps the backtrace for the
      current task as does dump_stack().  On some archs, dump_stack() prints
      extra information - pid, utsname and so on - in addition to the
      backtrace while the two are identical on other archs.
      
      The usages in arch-independent code of the two functions indicate
      show_stack(NULL, NULL) should print out bare backtrace while
      dump_stack() is used for debugging purposes when something went wrong,
      so it does make sense to print additional information on the task which
      triggered dump_stack().
      
      There's no reason to require archs to implement two separate but mostly
      identical functions.  It leads to unnecessary subtle information.
      
      This patch expands the dummy fallback dump_stack() implementation in
      lib/dump_stack.c such that it prints out debug information (taken from
      x86) and invokes show_stack(NULL, NULL) and drops arch-specific
      dump_stack() implementations in all archs except blackfin.  Blackfin's
      dump_stack() does something wonky that I don't understand.
      
      Debug information can be printed separately by calling
      dump_stack_print_info() so that arch-specific dump_stack()
      implementation can still emit the same debug information.  This is used
      in blackfin.
      
      This patch brings the following behavior changes.
      
      * On some archs, an extra level in backtrace for show_stack() could be
        printed.  This is because the top frame was determined in
        dump_stack() on those archs while generic dump_stack() can't do that
        reliably.  It can be compensated by inlining dump_stack() but not
        sure whether that'd be necessary.
      
      * Most archs didn't use to print debug info on dump_stack().  They do
        now.
      
      An example WARN dump follows.
      
       WARNING: at kernel/workqueue.c:4841 init_workqueues+0x35/0x505()
       Hardware name: empty
       Modules linked in:
       CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.9.0-rc1-work+ #9
        0000000000000009 ffff88007c861e08 ffffffff81c614dc ffff88007c861e48
        ffffffff8108f50f ffffffff82228240 0000000000000040 ffffffff8234a03c
        0000000000000000 0000000000000000 0000000000000000 ffff88007c861e58
       Call Trace:
        [<ffffffff81c614dc>] dump_stack+0x19/0x1b
        [<ffffffff8108f50f>] warn_slowpath_common+0x7f/0xc0
        [<ffffffff8108f56a>] warn_slowpath_null+0x1a/0x20
        [<ffffffff8234a071>] init_workqueues+0x35/0x505
        ...
      
      v2: CPU number added to the generic debug info as requested by s390
          folks and dropped the s390 specific dump_stack().  This loses %ksp
          from the debug message which the maintainers think isn't important
          enough to keep the s390-specific dump_stack() implementation.
      
          dump_stack_print_info() is moved to kernel/printk.c from
          lib/dump_stack.c.  Because linkage is per objecct file,
          dump_stack_print_info() living in the same lib file as generic
          dump_stack() means that archs which implement custom dump_stack()
          - at this point, only blackfin - can't use dump_stack_print_info()
          as that will bring in the generic version of dump_stack() too.  v1
          The v1 patch broke build on blackfin due to this issue.  The build
          breakage was reported by Fengguang Wu.
      Signed-off-by: NTejun Heo <tj@kernel.org>
      Acked-by: NDavid S. Miller <davem@davemloft.net>
      Acked-by: NVineet Gupta <vgupta@synopsys.com>
      Acked-by: NJesper Nilsson <jesper.nilsson@axis.com>
      Acked-by: NVineet Gupta <vgupta@synopsys.com>
      Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>	[s390 bits]
      Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
      Cc: Mike Frysinger <vapier@gentoo.org>
      Cc: Fengguang Wu <fengguang.wu@intel.com>
      Cc: Bjorn Helgaas <bhelgaas@google.com>
      Cc: Sam Ravnborg <sam@ravnborg.org>
      Acked-by: Richard Kuo <rkuo@codeaurora.org>		[hexagon bits]
      Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      196779b9
  12. 29 4月, 2013 1 次提交
  13. 08 4月, 2013 1 次提交
  14. 18 2月, 2013 1 次提交
  15. 04 2月, 2013 1 次提交
  16. 04 1月, 2013 1 次提交
    • G
      ARCH: drivers remove __dev* attributes. · b881bc46
      Greg Kroah-Hartman 提交于
      This fixes up all of the smaller arches that had __dev* markings for
      their platform-specific drivers.
      
      CONFIG_HOTPLUG is going away as an option.  As a result, the __dev*
      markings need to be removed.
      
      This change removes the use of __devinit, __devexit_p, __devinitdata,
      __devinitconst, and __devexit from these drivers.
      
      Based on patches originally written by Bill Pemberton, but redone by me
      in order to handle some of the coding style issues better, by hand.
      
      Cc: Bill Pemberton <wfp5p@virginia.edu>
      Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
      Cc: Paul Mackerras <paulus@samba.org>
      Cc: Ingo Molnar <mingo@redhat.com>
      Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
      Cc: Catalin Marinas <catalin.marinas@arm.com>
      Cc: Will Deacon <will.deacon@arm.com>
      Cc: Haavard Skinnemoen <hskinnemoen@gmail.com>
      Cc: Hans-Christian Egtvedt <egtvedt@samfundet.no>
      Cc: Mike Frysinger <vapier@gentoo.org>
      Cc: Mikael Starvik <starvik@axis.com>
      Cc: Jesper Nilsson <jesper.nilsson@axis.com>
      Cc: David Howells <dhowells@redhat.com>
      Cc: Hirokazu Takata <takata@linux-m32r.org>
      Cc: Geert Uytterhoeven <geert@linux-m68k.org>
      Cc: Michal Simek <monstr@monstr.eu>
      Cc: Koichi Yasutake <yasutake.koichi@jp.panasonic.com>
      Cc: Jonas Bonn <jonas@southpole.se>
      Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
      Cc: Helge Deller <deller@gmx.de>
      Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
      Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
      Cc: Chen Liqin <liqin.chen@sunplusct.com>
      Cc: Lennox Wu <lennox.wu@gmail.com>
      Cc: Paul Mundt <lethal@linux-sh.org>
      Cc: Chris Metcalf <cmetcalf@tilera.com>
      Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
      Cc: Bob Liu <lliubbo@gmail.com>
      Cc: Srinivas Kandagatla <srinivas.kandagatla@st.com>
      Cc: Bjorn Helgaas <bhelgaas@google.com>
      Cc: Myron Stowe <myron.stowe@redhat.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Andi Kleen <ak@linux.intel.com>
      Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
      Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
      Cc: Yinghai Lu <yinghai@kernel.org>
      Cc: Thierry Reding <thierry.reding@avionic-design.de>
      Cc: Greg Ungerer <gerg@uclinux.org>
      Cc: Grant Likely <grant.likely@secretlab.ca>
      Cc: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
      Cc: Mark Salter <msalter@redhat.com>
      Cc: Yong Zhang <yong.zhang0@gmail.com>
      Cc: Michael Holzheu <holzheu@linux.vnet.ibm.com>
      Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
      Cc: Jan Glauber <jang@linux.vnet.ibm.com>
      Cc: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
      Cc: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
      Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      b881bc46
  17. 25 12月, 2012 1 次提交
    • S
      time: convert arch_gettimeoffset to a pointer · 7b1f6207
      Stephen Warren 提交于
      Currently, whenever CONFIG_ARCH_USES_GETTIMEOFFSET is enabled, each
      arch core provides a single implementation of arch_gettimeoffset(). In
      many cases, different sub-architectures, different machines, or
      different timer providers exist, and so the arch ends up implementing
      arch_gettimeoffset() as a call-through-pointer anyway. Examples are
      ARM, Cris, M68K, and it's arguable that the remaining architectures,
      M32R and Blackfin, should be doing this anyway.
      
      Modify arch_gettimeoffset so that it itself is a function pointer, which
      the arch initializes. This will allow later changes to move the
      initialization of this function into individual machine support or timer
      drivers. This is particularly useful for code in drivers/clocksource
      which should rely on an arch-independant mechanism to register their
      implementation of arch_gettimeoffset().
      
      This patch also converts the Cris architecture to set arch_gettimeoffset
      directly to the final implementation in time_init(), because Cris already
      had separate time_init() functions per sub-architecture. M68K and ARM
      are converted to set arch_gettimeoffset to the final implementation in
      later patches, because they already have function pointers in place for
      this purpose.
      
      Cc: Russell King <linux@arm.linux.org.uk>
      Cc: Mike Frysinger <vapier@gentoo.org>
      Cc: Mikael Starvik <starvik@axis.com>
      Cc: Hirokazu Takata <takata@linux-m32r.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Acked-by: NGeert Uytterhoeven <geert@linux-m68k.org>
      Acked-by: NJesper Nilsson <jesper.nilsson@axis.com>
      Acked-by: NJohn Stultz <johnstul@us.ibm.com>
      Signed-off-by: NStephen Warren <swarren@nvidia.com>
      7b1f6207
  18. 29 11月, 2012 3 次提交
  19. 01 11月, 2012 2 次提交
  20. 13 10月, 2012 1 次提交
    • J
      vfs: define struct filename and have getname() return it · 91a27b2a
      Jeff Layton 提交于
      getname() is intended to copy pathname strings from userspace into a
      kernel buffer. The result is just a string in kernel space. It would
      however be quite helpful to be able to attach some ancillary info to
      the string.
      
      For instance, we could attach some audit-related info to reduce the
      amount of audit-related processing needed. When auditing is enabled,
      we could also call getname() on the string more than once and not
      need to recopy it from userspace.
      
      This patchset converts the getname()/putname() interfaces to return
      a struct instead of a string. For now, the struct just tracks the
      string in kernel space and the original userland pointer for it.
      
      Later, we'll add other information to the struct as it becomes
      convenient.
      Signed-off-by: NJeff Layton <jlayton@redhat.com>
      Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      91a27b2a
  21. 01 10月, 2012 2 次提交
  22. 28 9月, 2012 1 次提交
    • D
      Make most arch asm/module.h files use asm-generic/module.h · 786d35d4
      David Howells 提交于
      Use the mapping of Elf_[SPE]hdr, Elf_Addr, Elf_Sym, Elf_Dyn, Elf_Rel/Rela,
      ELF_R_TYPE() and ELF_R_SYM() to either the 32-bit version or the 64-bit version
      into asm-generic/module.h for all arches bar MIPS.
      
      Also, use the generic definition mod_arch_specific where possible.
      
      To this end, I've defined three new config bools:
      
       (*) HAVE_MOD_ARCH_SPECIFIC
      
           Arches define this if they don't want to use the empty generic
           mod_arch_specific struct.
      
       (*) MODULES_USE_ELF_RELA
      
           Arches define this if their modules can contain RELA records.  This causes
           the Elf_Rela mapping to be emitted and allows apply_relocate_add() to be
           defined by the arch rather than have the core emit an error message.
      
       (*) MODULES_USE_ELF_REL
      
           Arches define this if their modules can contain REL records.  This causes
           the Elf_Rel mapping to be emitted and allows apply_relocate() to be
           defined by the arch rather than have the core emit an error message.
      
      Note that it is possible to allow both REL and RELA records: m68k and mips are
      two arches that do this.
      
      With this, some arch asm/module.h files can be deleted entirely and replaced
      with a generic-y marker in the arch Kbuild file.
      
      Additionally, I have removed the bits from m32r and score that handle the
      unsupported type of relocation record as that's now handled centrally.
      Signed-off-by: NDavid Howells <dhowells@redhat.com>
      Acked-by: NSam Ravnborg <sam@ravnborg.org>
      Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>
      786d35d4
  23. 23 9月, 2012 1 次提交
  24. 18 7月, 2012 2 次提交
  25. 02 6月, 2012 6 次提交
  26. 24 5月, 2012 1 次提交
  27. 22 5月, 2012 1 次提交
    • M
      m32r: use set_current_blocked() and block_sigmask() · 3883e301
      Matt Fleming 提交于
      As described in e6fa16ab ("signal: sigprocmask() should do
      retarget_shared_pending()") the modification of current->blocked is
      incorrect as we need to check whether the signal we're about to block is
      pending in the shared queue.
      
      Also, use the new helper function introduced in commit 5e6292c0
      ("signal: add block_sigmask() for adding sigmask to current->blocked")
      which centralises the code for updating current->blocked after
      successfully delivering a signal and reduces the amount of duplicate code
      across architectures.  In the past some architectures got this code wrong,
      so using this helper function should stop that from happening again.
      Acked-by: NOleg Nesterov <oleg@redhat.com>
      Cc: Hirokazu Takata <takata@linux-m32r.org>
      Cc: Al Viro <viro@zeniv.linux.org.uk>
      Cc: Kyle McMartin <kyle@redhat.com>
      Signed-off-by: NMatt Fleming <matt.fleming@intel.com>
      Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      3883e301