1. 11 Sep, 2015 1 commit
    • Mathieu Desnoyers's avatar
      sys_membarrier(): system-wide memory barrier (generic, x86) · 5b25b13a
      Mathieu Desnoyers authored
      Here is an implementation of a new system call, sys_membarrier(), which
      executes a memory barrier on all threads running on the system.  It is
      implemented by calling synchronize_sched().  It can be used to
      distribute the cost of user-space memory barriers asymmetrically by
      transforming pairs of memory barriers into pairs consisting of
      sys_membarrier() and a compiler barrier.  For synchronization primitives
      that distinguish between read-side and write-side (e.g.  userspace RCU
      [1], rwlocks), the read-side can be accelerated significantly by moving
      the bulk of the memory barrier overhead to the write-side.
      The existing applications of which I am aware that would be improved by
      this system call are as follows:
      * Through Userspace RCU library (http://urcu.so)
        - DNS server (Knot DNS) https://www.knot-dns.cz/
        - Network sniffer (http://netsniff-ng.org/)
        - Distributed object storage (https://sheepdog.github.io/sheepdog/)
        - User-space tracing (http://lttng.org)
        - Network storage system (https://www.gluster.org/)
        - Virtual routers (https://events.linuxfoundation.org/sites/events/files/slides/DPDK_RCU_0MQ.pdf)
        - Financial software (https://lkml.org/lkml/2015/3/23/189)
      Those projects use RCU in userspace to increase read-side speed and
      scalability compared to locking.  Especially in the case of RCU used by
      libraries, sys_membarrier can speed up the read-side by moving the bulk of
      the memory barrier cost to synchronize_rcu().
      * Direct users of sys_membarrier
        - core dotnet garbage collector (https://github.com/dotnet/coreclr/issues/198)
      Microsoft core dotnet GC developers are planning to use the mprotect()
      side-effect of issuing memory barriers through IPIs as a way to implement
      Windows FlushProcessWriteBuffers() on Linux.  They are referring to
      sys_membarrier in their github thread, specifically stating that
      sys_membarrier() is what they are looking for.
      To explain the benefit of this scheme, let's introduce two example threads:
      Thread A (non-frequent, e.g. executing liburcu synchronize_rcu())
      Thread B (frequent, e.g. executing liburcu
      In a scheme where all smp_mb() in thread A are ordering memory accesses
      with respect to smp_mb() present in Thread B, we can change each
      smp_mb() within Thread A into calls to sys_membarrier() and each
      smp_mb() within Thread B into compiler barriers "barrier()".
      Before the change, we had, for each smp_mb() pairs:
      Thread A                    Thread B
      previous mem accesses       previous mem accesses
      smp_mb()                    smp_mb()
      following mem accesses      following mem accesses
      After the change, these pairs become:
      Thread A                    Thread B
      prev mem accesses           prev mem accesses
      sys_membarrier()            barrier()
      follow mem accesses         follow mem accesses
      As we can see, there are two possible scenarios: either Thread B memory
      accesses do not happen concurrently with Thread A accesses (1), or they
      do (2).
      1) Non-concurrent Thread A vs Thread B accesses:
      Thread A                    Thread B
      prev mem accesses
      follow mem accesses
                                  prev mem accesses
                                  follow mem accesses
      In this case, thread B accesses will be weakly ordered. This is OK,
      because at that point, thread A is not particularly interested in
      ordering them with respect to its own accesses.
      2) Concurrent Thread A vs Thread B accesses
      Thread A                    Thread B
      prev mem accesses           prev mem accesses
      sys_membarrier()            barrier()
      follow mem accesses         follow mem accesses
      In this case, thread B accesses, which are ensured to be in program
      order thanks to the compiler barrier, will be "upgraded" to full
      smp_mb() by synchronize_sched().
      * Benchmarks
      On Intel Xeon E5405 (8 cores)
      (one thread is calling sys_membarrier, the other 7 threads are busy
      1000 non-expedited sys_membarrier calls in 33s =3D 33 milliseconds/call.
      * User-space user of this system call: Userspace RCU library
      Both the signal-based and the sys_membarrier userspace RCU schemes
      permit us to remove the memory barrier from the userspace RCU
      rcu_read_lock() and rcu_read_unlock() primitives, thus significantly
      accelerating them. These memory barriers are replaced by compiler
      barriers on the read-side, and all matching memory barriers on the
      write-side are turned into an invocation of a memory barrier on all
      active threads in the process. By letting the kernel perform this
      synchronization rather than dumbly sending a signal to every process
      threads (as we currently do), we diminish the number of unnecessary wake
      ups and only issue the memory barriers on active threads. Non-running
      threads do not need to execute such barrier anyway, because these are
      implied by the scheduler context switches.
      Results in liburcu:
      Operations in 10s, 6 readers, 2 writers:
      memory barriers in reader:    1701557485 reads, 2202847 writes
      signal-based scheme:          9830061167 reads,    6700 writes
      sys_membarrier:               9952759104 reads,     425 writes
      sys_membarrier (dyn. check):  7970328887 reads,     425 writes
      The dynamic sys_membarrier availability check adds some overhead to
      the read-side compared to the signal-based scheme, but besides that,
      sys_membarrier slightly outperforms the signal-based scheme. However,
      this non-expedited sys_membarrier implementation has a much slower grace
      period than signal and memory barrier schemes.
      Besides diminishing the number of wake-ups, one major advantage of the
      membarrier system call over the signal-based scheme is that it does not
      need to reserve a signal. This plays much more nicely with libraries,
      and with processes injected into for tracing purposes, for which we
      cannot expect that signals will be unused by the application.
      An expedited version of this system call can be added later on to speed
      up the grace period. Its implementation will likely depend on reading
      the cpu_curr()->mm without holding each CPU's rq lock.
      This patch adds the system call to x86 and to asm-generic.
      [1] http://urcu.so
      membarrier(2) man page:
      MEMBARRIER(2)              Linux Programmer's Manual             MEMBARRIER(2)
             membarrier - issue memory barriers on a set of threads
             #include <linux/membarrier.h>
             int membarrier(int cmd, int flags);
             The cmd argument is one of the following:
                    Query  the  set  of  supported commands. It returns a bitmask of
                    supported commands.
                    Execute a memory barrier on all threads running on  the  system.
                    Upon  return from system call, the caller thread is ensured that
                    all running threads have passed through a state where all memory
                    accesses  to  user-space  addresses  match program order between
                    entry to and return from the system  call  (non-running  threads
                    are de facto in such a state). This covers threads from all pro=E2=80=90
                    cesses running on the system.  This command returns 0.
             The flags argument needs to be 0. For future extensions.
             All memory accesses performed  in  program  order  from  each  targeted
             thread is guaranteed to be ordered with respect to sys_membarrier(). If
             we use the semantic "barrier()" to represent a compiler barrier forcing
             memory  accesses  to  be performed in program order across the barrier,
             and smp_mb() to represent explicit memory barriers forcing full  memory
             ordering  across  the barrier, we have the following ordering table for
             each pair of barrier(), sys_membarrier() and smp_mb():
             The pair ordering is detailed as (O: ordered, X: not ordered):
                                    barrier()   smp_mb() sys_membarrier()
                    barrier()          X           X            O
                    smp_mb()           X           O            O
                    sys_membarrier()   O           O            O
             On success, these system calls return zero.  On error, -1 is  returned,
             and errno is set appropriately. For a given command, with flags
             argument set to 0, this system call is guaranteed to always return the
             same value until reboot.
             ENOSYS System call is not implemented.
             EINVAL Invalid arguments.
      Linux                             2015-04-15                     MEMBARRIER(2)
      Signed-off-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
      Reviewed-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
      Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Nicholas Miell <nmiell@comcast.net>
      Cc: Ingo Molnar <mingo@redhat.com>
      Cc: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
      Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
      Cc: Stephen Hemminger <stephen@networkplumber.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: David Howells <dhowells@redhat.com>
      Cc: Pranith Kumar <bobby.prani@gmail.com>
      Cc: Michael Kerrisk <mtk.manpages@gmail.com>
      Cc: Shuah Khan <shuahkh@osg.samsung.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
  2. 10 Sep, 2015 2 commits
    • Dave Young's avatar
      kexec: split kexec_load syscall from kexec core code · 2965faa5
      Dave Young authored
      There are two kexec load syscalls, kexec_load another and kexec_file_load.
       kexec_file_load has been splited as kernel/kexec_file.c.  In this patch I
      split kexec_load syscall code to kernel/kexec.c.
      And add a new kconfig option KEXEC_CORE, so we can disable kexec_load and
      use kexec_file_load only, or vice verse.
      The original requirement is from Ted Ts'o, he want kexec kernel signature
      being checked with CONFIG_KEXEC_VERIFY_SIG enabled.  But kexec-tools use
      kexec_load syscall can bypass the checking.
      Vivek Goyal proposed to create a common kconfig option so user can compile
      in only one syscall for loading kexec kernel.  KEXEC/KEXEC_FILE selects
      KEXEC_CORE so that old config files still work.
      Because there's general code need CONFIG_KEXEC_CORE, so I updated all the
      architecture Kconfig with a new option KEXEC_CORE, and let KEXEC selects
      KEXEC_CORE in arch Kconfig.  Also updated general kernel code with to
      kexec_load syscall.
      [akpm@linux-foundation.org: coding-style fixes]
      Signed-off-by: default avatarDave Young <dyoung@redhat.com>
      Cc: Eric W. Biederman <ebiederm@xmission.com>
      Cc: Vivek Goyal <vgoyal@redhat.com>
      Cc: Petr Tesarik <ptesarik@suse.cz>
      Cc: Theodore Ts'o <tytso@mit.edu>
      Cc: Josh Boyer <jwboyer@fedoraproject.org>
      Cc: David Howells <dhowells@redhat.com>
      Cc: Geert Uytterhoeven <geert@linux-m68k.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    • Frederic Weisbecker's avatar
      kmod: use system_unbound_wq instead of khelper · 90f02303
      Frederic Weisbecker authored
      We need to launch the usermodehelper kernel threads with the widest
      affinity and this is partly why we use khelper.  This workqueue has
      unbound properties and thus a wide affinity inherited by all its children.
      Now khelper also has special properties that we aren't much interested in:
      ordered and singlethread.  There is really no need about ordering as all
      we do is creating kernel threads.  This can be done concurrently.  And
      singlethread is a useless limitation as well.
      The workqueue engine already proposes generic unbound workqueues that
      don't share these useless properties and handle well parallel jobs.
      The only worrysome specific is their affinity to the node of the current
      CPU.  It's fine for creating the usermodehelper kernel threads but those
      inherit this affinity for longer jobs such as requesting modules.
      This patch proposes to use these node affine unbound workqueues assuming
      that a node is sufficient to handle several parallel usermodehelper
      Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Rik van Riel <riel@redhat.com>
      Reviewed-by: default avatarOleg Nesterov <oleg@redhat.com>
      Cc: Christoph Lameter <cl@linux.com>
      Cc: Tejun Heo <tj@kernel.org>
      Cc: Rusty Russell <rusty@rustcorp.com.au>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
  3. 04 Sep, 2015 2 commits
    • Mel Gorman's avatar
      mm: send one IPI per CPU to TLB flush all entries after unmapping pages · 72b252ae
      Mel Gorman authored
      An IPI is sent to flush remote TLBs when a page is unmapped that was
      potentially accesssed by other CPUs.  There are many circumstances where
      this happens but the obvious one is kswapd reclaiming pages belonging to a
      running process as kswapd and the task are likely running on separate
      On small machines, this is not a significant problem but as machine gets
      larger with more cores and more memory, the cost of these IPIs can be
      high.  This patch uses a simple structure that tracks CPUs that
      potentially have TLB entries for pages being unmapped.  When the unmapping
      is complete, the full TLB is flushed on the assumption that a refill cost
      is lower than flushing individual entries.
      Architectures wishing to do this must give the following guarantee.
              If a clean page is unmapped and not immediately flushed, the
              architecture must guarantee that a write to that linear address
              from a CPU with a cached TLB entry will trap a page fault.
      This is essentially what the kernel already depends on but the window is
      much larger with this patch applied and is worth highlighting.  The
      architecture should consider whether the cost of the full TLB flush is
      higher than sending an IPI to flush each individual entry.  An additional
      architecture helper called flush_tlb_local is required.  It's a trivial
      wrapper with some accounting in the x86 case.
      The impact of this patch depends on the workload as measuring any benefit
      requires both mapped pages co-located on the LRU and memory pressure.  The
      case with the biggest impact is multiple processes reading mapped pages
      taken from the vm-scalability test suite.  The test case uses NR_CPU
      readers of mapped files that consume 10*RAM.
      Linear mapped reader on a 4-node machine with 64G RAM and 48 CPUs
                                                 4.2.0-rc1          4.2.0-rc1
                                                   vanilla       flushfull-v7
      Ops lru-file-mmap-read-elapsed      159.62 (  0.00%)   120.68 ( 24.40%)
      Ops lru-file-mmap-read-time_range    30.59 (  0.00%)     2.80 ( 90.85%)
      Ops lru-file-mmap-read-time_stddv     6.70 (  0.00%)     0.64 ( 90.38%)
                 4.2.0-rc1    4.2.0-rc1
                   vanilla flushfull-v7
      User          581.00       611.43
      System       5804.93      4111.76
      Elapsed       161.03       122.12
      This is showing that the readers completed 24.40% faster with 29% less
      system CPU time.  From vmstats, it is known that the vanilla kernel was
      interrupted roughly 900K times per second during the steady phase of the
      test and the patched kernel was interrupts 180K times per second.
      The impact is lower on a single socket machine.
                                                 4.2.0-rc1          4.2.0-rc1
                                                   vanilla       flushfull-v7
      Ops lru-file-mmap-read-elapsed       25.33 (  0.00%)    20.38 ( 19.54%)
      Ops lru-file-mmap-read-time_range     0.91 (  0.00%)     1.44 (-58.24%)
      Ops lru-file-mmap-read-time_stddv     0.28 (  0.00%)     0.47 (-65.34%)
                 4.2.0-rc1    4.2.0-rc1
                   vanilla flushfull-v7
      User           58.09        57.64
      System        111.82        76.56
      Elapsed        27.29        22.55
      It's still a noticeable improvement with vmstat showing interrupts went
      from roughly 500K per second to 45K per second.
      The patch will have no impact on workloads with no memory pressure or have
      relatively few mapped pages.  It will have an unpredictable impact on the
      workload running on the CPU being flushed as it'll depend on how many TLB
      entries need to be refilled and how long that takes.  Worst case, the TLB
      will be completely cleared of active entries when the target PFNs were not
      resident at all.
      [sasha.levin@oracle.com: trace tlb flush after disabling preemption in try_to_unmap_flush]
      Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
      Reviewed-by: default avatarRik van Riel <riel@redhat.com>
      Cc: Dave Hansen <dave.hansen@intel.com>
      Acked-by: default avatarIngo Molnar <mingo@kernel.org>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Signed-off-by: default avatarSasha Levin <sasha.levin@oracle.com>
      Cc: Michal Hocko <mhocko@suse.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    • Andrea Arcangeli's avatar
      userfaultfd: buildsystem activation · a14c151e
      Andrea Arcangeli authored
      This allows to select the userfaultfd during configuration to build it.
      Signed-off-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
      Acked-by: default avatarPavel Emelyanov <xemul@parallels.com>
      Cc: Sanidhya Kashyap <sanidhya.gatech@gmail.com>
      Cc: zhang.zhanghailiang@huawei.com
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Andres Lagar-Cavilla <andreslc@google.com>
      Cc: Dave Hansen <dave.hansen@intel.com>
      Cc: Paolo Bonzini <pbonzini@redhat.com>
      Cc: Rik van Riel <riel@redhat.com>
      Cc: Mel Gorman <mgorman@suse.de>
      Cc: Andy Lutomirski <luto@amacapital.net>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Peter Feiner <pfeiner@google.com>
      Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
      Cc: Johannes Weiner <hannes@cmpxchg.org>
      Cc: "Huangpeng (Peter)" <peter.huangpeng@huawei.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
  4. 15 Aug, 2015 1 commit
  5. 14 Aug, 2015 1 commit
  6. 12 Aug, 2015 1 commit
  7. 07 Aug, 2015 6 commits
  8. 06 Aug, 2015 1 commit
    • Mel Gorman's avatar
      fs, file table: reinit files_stat.max_files after deferred memory initialisation · 4248b0da
      Mel Gorman authored
      Dave Hansen reported the following;
      	My laptop has been behaving strangely with 4.2-rc2.  Once I log
      	in to my X session, I start getting all kinds of strange errors
      	from applications and see this in my dmesg:
              	VFS: file-max limit 8192 reached
      The problem is that the file-max is calculated before memory is fully
      initialised and miscalculates how much memory the kernel is using.  This
      patch recalculates file-max after deferred memory initialisation.  Note
      that using memory hotplug infrastructure would not have avoided this
      problem as the value is not recalculated after memory hot-add.
      4.1:             files_stat.max_files = 6582781
      4.2-rc2:         files_stat.max_files = 8192
      4.2-rc2 patched: files_stat.max_files = 6562467
      Small differences with the patch applied and 4.1 but not enough to matter.
      Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
      Reported-by: default avatarDave Hansen <dave.hansen@intel.com>
      Cc: Nicolai Stange <nicstange@gmail.com>
      Cc: Dave Hansen <dave.hansen@intel.com>
      Cc: Alex Ng <alexng@microsoft.com>
      Cc: Fengguang Wu <fengguang.wu@intel.com>
      Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
  9. 22 Jul, 2015 1 commit
  10. 14 Jul, 2015 1 commit
    • Aleksa Sarai's avatar
      cgroup: implement the PIDs subsystem · 49b786ea
      Aleksa Sarai authored
      Adds a new single-purpose PIDs subsystem to limit the number of
      tasks that can be forked inside a cgroup. Essentially this is an
      implementation of RLIMIT_NPROC that applies to a cgroup rather than a
      process tree.
      However, it should be noted that organisational operations (adding and
      removing tasks from a PIDs hierarchy) will *not* be prevented. Rather,
      the number of tasks in the hierarchy cannot exceed the limit through
      forking. This is due to the fact that, in the unified hierarchy, attach
      cannot fail (and it is not possible for a task to overcome its PIDs
      cgroup policy limit by attaching to a child cgroup -- even if migrating
      mid-fork it must be able to fork in the parent first).
      PIDs are fundamentally a global resource, and it is possible to reach
      PID exhaustion inside a cgroup without hitting any reasonable kmemcg
      policy. Once you've hit PID exhaustion, you're only in a marginally
      better state than OOM. This subsystem allows PID exhaustion inside a
      cgroup to be prevented.
      Signed-off-by: default avatarAleksa Sarai <cyphar@cyphar.com>
      Signed-off-by: default avatarTejun Heo <tj@kernel.org>
  11. 06 Jul, 2015 1 commit
  12. 04 Jul, 2015 1 commit
  13. 01 Jul, 2015 1 commit
    • Ingo Molnar's avatar
      printk: Increase maximum CONFIG_LOG_BUF_SHIFT from 21 to 25 · fb39f98d
      Ingo Molnar authored
      So I tried to some kernel debugging that produced a ton of kernel messages
      on a big box, and wanted to save them all: but CONFIG_LOG_BUF_SHIFT maxes
      out at 21 (2 MB).
      Increase it to 25 (32 MB).
      This does not affect any existing config or defaults.
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: linux-kernel@vger.kernel.org
      Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
  14. 30 Jun, 2015 1 commit
    • Mel Gorman's avatar
      mm: meminit: finish initialisation of struct pages before basic setup · 0e1cc95b
      Mel Gorman authored
      Waiman Long reported that 24TB machines hit OOM during basic setup when
      struct page initialisation was deferred.  One approach is to initialise
      memory on demand but it interferes with page allocator paths.  This patch
      creates dedicated threads to initialise memory before basic setup.  It
      then blocks on a rw_semaphore until completion as a wait_queue and counter
      is overkill.  This may be slower to boot but it's simplier overall and
      also gets rid of a section mangling which existed so kswapd could do the
      [akpm@linux-foundation.org: include rwsem.h, use DECLARE_RWSEM, fix comment, remove unneeded cast]
      Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
      Cc: Waiman Long <waiman.long@hp.com
      Cc: Nathan Zimmer <nzimmer@sgi.com>
      Cc: Dave Hansen <dave.hansen@intel.com>
      Cc: Scott Norton <scott.norton@hp.com>
      Tested-by: default avatarDaniel J Blueman <daniel@numascale.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
  15. 25 Jun, 2015 2 commits
    • Vishnu Pratap Singh's avatar
      init/do_mounts.c: add create_dev() failure log · c69e3c3a
      Vishnu Pratap Singh authored
      If create_dev() function fails to create the root mount device
      (/dev/root), then it goes to panic as root device not found but there is
      no printk in this case.  So I have added the log in case it fails to
      create the root device.  It will help in debugging.
      [akpm@linux-foundation.org: simplify printk(), use pr_emerg(), display errno]
      Signed-off-by: default avatarVishnu Pratap Singh <vishnu.ps@samsung.com>
      Acked-by: default avatarPavel Machek <pavel@ucw.cz>
      Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
      Cc: Mike Snitzer <snitzer@redhat.com>
      Cc: Dan Ehrenberg <dehrenberg@chromium.org>
      Cc: Miklos Szeredi <mszeredi@suse.cz>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    • Iago López Galeiras's avatar
      fs, proc: introduce CONFIG_PROC_CHILDREN · 2e13ba54
      Iago López Galeiras authored
      Commit 81841161 ("fs, proc: introduce /proc/<pid>/task/<tid>/children
      entry") introduced the children entry for checkpoint restore and the
      file is only available on kernels configured with CONFIG_EXPERT and
      This is available in most distributions (Fedora, Debian, Ubuntu, CoreOS)
      because they usually enable CONFIG_EXPERT and CONFIG_CHECKPOINT_RESTORE.
      But Arch does not enable CONFIG_EXPERT or CONFIG_CHECKPOINT_RESTORE.
      However, the children proc file is useful outside of checkpoint restore.
      I would like to use it in rkt.  The rkt process exec() another program
      it does not control, and that other program will fork()+exec() a child
      process.  I would like to find the pid of the child process from an
      external tool without iterating in /proc over all processes to find
      which one has a parent pid equal to rkt.
      This commit introduces CONFIG_PROC_CHILDREN and makes
      CONFIG_CHECKPOINT_RESTORE select it.  This allows enabling
      /proc/<pid>/task/<tid>/children without needing to enable
      Alban tested that /proc/<pid>/task/<tid>/children is present when the
      kernel is configured with CONFIG_PROC_CHILDREN=y but without
      Signed-off-by: default avatarIago López Galeiras <iago@endocode.com>
      Tested-by: default avatarAlban Crequy <alban@endocode.com>
      Reviewed-by: default avatarCyrill Gorcunov <gorcunov@openvz.org>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Kees Cook <keescook@chromium.org>
      Cc: Pavel Emelyanov <xemul@parallels.com>
      Cc: Serge Hallyn <serge.hallyn@canonical.com>
      Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
      Cc: Alexander Viro <viro@zeniv.linux.org.uk>
      Cc: Andy Lutomirski <luto@amacapital.net>
      Cc: Djalal Harouni <djalal@endocode.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
  16. 22 Jun, 2015 1 commit
  17. 10 Jun, 2015 1 commit
    • Rafael J. Wysocki's avatar
      ACPI / init: Switch over platform to the ACPI mode later · b064a8fa
      Rafael J. Wysocki authored
      Commit 73f7d1ca "ACPI / init: Run acpi_early_init() before
      timekeeping_init()" moved the ACPI subsystem initialization,
      including the ACPI mode enabling, to an earlier point in the
      initialization sequence, to allow the timekeeping subsystem
      use ACPI early.  Unfortunately, that resulted in boot regressions
      on some systems and the early ACPI initialization was moved toward
      its original position in the kernel initialization code by commit
      c4e1acbb "ACPI / init: Invoke early ACPI initialization later".
      However, that turns out to be insufficient, as boot is still broken
      on the Tyan S8812 mainboard.
      To fix that issue, split the ACPI early initialization code into
      two pieces so the majority of it still located in acpi_early_init()
      and the part switching over the platform into the ACPI mode goes into
      a new function, acpi_subsystem_init(), executed at the original early
      ACPI initialization spot.
      That fixes the Tyan S8812 boot problem, but still allows ACPI
      tables to be loaded earlier which is useful to the EFI code in
      Link: https://bugzilla.kernel.org/show_bug.cgi?id=97141
      Fixes: 73f7d1ca "ACPI / init: Run acpi_early_init() before timekeeping_init()"
      Reported-and-tested-by: default avatarMarius Tolzmann <tolzmann@molgen.mpg.de>
      Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
      Acked-by: default avatarToshi Kani <toshi.kani@hp.com>
      Reviewed-by: default avatarHanjun Guo <hanjun.guo@linaro.org>
      Reviewed-by: default avatarLee, Chun-Yi <jlee@suse.com>
  18. 02 Jun, 2015 1 commit
    • Tejun Heo's avatar
      writeback: add {CONFIG|BDI_CAP|FS}_CGROUP_WRITEBACK · 89e9b9e0
      Tejun Heo authored
      cgroup writeback requires support from both bdi and filesystem sides.
      support and enable BDI_CAP_CGROUP_WRITEBACK on block based bdi's by
      default.  Also, define CONFIG_CGROUP_WRITEBACK which is enabled if
      both MEMCG and BLK_CGROUP are enabled.
      inode_cgwb_enabled() which determines whether a given inode's both bdi
      and fs support cgroup writeback is added.
      Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      Cc: Jens Axboe <axboe@kernel.dk>
      Cc: Jan Kara <jack@suse.cz>
      Signed-off-by: default avatarJens Axboe <axboe@fb.com>
  19. 27 May, 2015 10 commits
  20. 26 May, 2015 1 commit
    • Tejun Heo's avatar
      sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem · d59cfc09
      Tejun Heo authored
      The cgroup side of threadgroup locking uses signal_struct->group_rwsem
      to synchronize against threadgroup changes.  This per-process rwsem
      adds small overhead to thread creation, exit and exec paths, forces
      cgroup code paths to do lock-verify-unlock-retry dance in a couple
      places and makes it impossible to atomically perform operations across
      multiple processes.
      This patch replaces signal_struct->group_rwsem with a global
      percpu_rwsem cgroup_threadgroup_rwsem which is cheaper on the reader
      side and contained in cgroups proper.  This patch converts one-to-one.
      This does make writer side heavier and lower the granularity; however,
      cgroup process migration is a fairly cold path, we do want to optimize
      thread operations over it and cgroup migration operations don't take
      enough time for the lower granularity to matter.
      Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      Cc: Ingo Molnar <mingo@redhat.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
  21. 20 May, 2015 1 commit
    • Luis R. Rodriguez's avatar
      module: add extra argument for parse_params() callback · ecc86170
      Luis R. Rodriguez authored
      This adds an extra argument onto parse_params() to be used
      as a way to make the unused callback a bit more useful and
      generic by allowing the caller to pass on a data structure
      of its choice. An example use case is to allow us to easily
      make module parameters for every module which we will do
      @ parse @
      identifier name, args, params, num, level_min, level_max;
      identifier unknown, param, val, doing;
      type s16;
       extern char *parse_args(const char *name,
       			 char *args,
       			 const struct kernel_param *params,
       			 unsigned num,
       			 s16 level_min,
       			 s16 level_max,
      +			 void *arg,
       			 int (*unknown)(char *param, char *val,
      					const char *doing
      +					, void *arg
      @ parse_mod @
      identifier name, args, params, num, level_min, level_max;
      identifier unknown, param, val, doing;
      type s16;
       char *parse_args(const char *name,
       			 char *args,
       			 const struct kernel_param *params,
       			 unsigned num,
       			 s16 level_min,
       			 s16 level_max,
      +			 void *arg,
       			 int (*unknown)(char *param, char *val,
      					const char *doing
      +					, void *arg
      @ parse_args_found @
      expression R, E1, E2, E3, E4, E5, E6;
      identifier func;
      	R =
      	parse_args(E1, E2, E3, E4, E5, E6,
      +		   NULL,
      	R =
      	parse_args(E1, E2, E3, E4, E5, E6,
      +		   NULL,
      	R =
      	parse_args(E1, E2, E3, E4, E5, E6,
      +		   NULL,
      	parse_args(E1, E2, E3, E4, E5, E6,
      +		   NULL,
      	parse_args(E1, E2, E3, E4, E5, E6,
      +		   NULL,
      	parse_args(E1, E2, E3, E4, E5, E6,
      +		   NULL,
      @ parse_args_unused depends on parse_args_found @
      identifier parse_args_found.func;
      int func(char *param, char *val, const char *unused
      +		 , void *arg
      @ mod_unused depends on parse_args_found @
      identifier parse_args_found.func;
      expression A1, A2, A3;
      -	func(A1, A2, A3);
      +	func(A1, A2, A3, NULL);
      Generated-by: Coccinelle SmPL
      Cc: cocci@systeme.lip6.fr
      Cc: Tejun Heo <tj@kernel.org>
      Cc: Arjan van de Ven <arjan@linux.intel.com>
      Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
      Cc: Rusty Russell <rusty@rustcorp.com.au>
      Cc: Christoph Hellwig <hch@infradead.org>
      Cc: Felipe Contreras <felipe.contreras@gmail.com>
      Cc: Ewan Milne <emilne@redhat.com>
      Cc: Jean Delvare <jdelvare@suse.de>
      Cc: Hannes Reinecke <hare@suse.de>
      Cc: Jani Nikula <jani.nikula@intel.com>
      Cc: linux-kernel@vger.kernel.org
      Reviewed-by: default avatarTejun Heo <tj@kernel.org>
      Acked-by: default avatarRusty Russell <rusty@rustcorp.com.au>
      Signed-off-by: default avatarLuis R. Rodriguez <mcgrof@suse.com>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
  22. 08 May, 2015 1 commit
  23. 05 May, 2015 1 commit