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[RFC][PATCH 00/13] percpu rwsem -v2

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This is a derived work of the cpu hotplug lock rework I did in 2013 which never
really went anywhere because Linus didn't like it.

This applies those same optimizations to the percpu-rwsem. Seeing how we did
all the work it seemed a waste to not use it at all. Linus still didn't like it
because there was only a single user, there are two now:

 - uprobes
 - cgroups

This series converts the cpu hotplug lock into a percpu-rwsem to provide a 3rd
user.

Also, since Linus thinks lglocks is a failed locking primitive (which I whole
heartedly agree with, its preempt-disable latencies are an abomination), it
also converts the global part of fs/locks's usage of lglock over to a
percpu-rwsem and uses a per-cpu spinlock for the local part. This both provides
another (4th) percpu-rwsem users and removes an lglock user.

It further removes the stop_machine lglock usage, and with it kills lglocks.

Changes since -v1:

 - Added the missing smp_load_acquire()/smp_store_release() as spotted by Oleg
 - Added percpu_down_read_trylock()
 - Convert cpu hotplug lock
 - Convert fs/locks
 - Removes lglock from stop_machine
 - Removes lglock

---
 Documentation/locking/lglock.txt | 166 -------------------------
 fs/Kconfig                       |   1 +
 fs/file_table.c                  |   1 -
 fs/locks.c                       |  65 +++++++---
 include/linux/cpu.h              |   6 +
 include/linux/lglock.h           |  81 -------------
 include/linux/percpu-rwsem.h     |  96 +++++++++++++--
 include/linux/sched.h            |   9 +-
 init/main.c                      |   1 +
 kernel/cpu.c                     | 130 ++++++--------------
 kernel/fork.c                    |   2 +
 kernel/locking/Makefile          |   1 -
 kernel/locking/lglock.c          | 111 -----------------
 kernel/locking/percpu-rwsem.c    | 255 +++++++++++++++++++++------------------
 kernel/rcu/Makefile              |   2 +-
 kernel/stop_machine.c            |  52 ++++----
 lib/Kconfig                      |  10 ++
 17 files changed, 371 insertions(+), 618 deletions(-)

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[RFC][PATCH 00/13] percpu rwsem -v2 Peter Zijlstra <peterz@infradead.org> - 2015-06-22 14:30 +0200
  [RFC][PATCH 01/13] rcu: Create rcu_sync infrastructure Peter Zijlstra <peterz@infradead.org> - 2015-06-22 14:30 +0200
  [RFC][PATCH 05/13] percpu-rwsem: Optimize readers and reduce global impact Peter Zijlstra <peterz@infradead.org> - 2015-06-22 14:30 +0200
    Re: [RFC][PATCH 05/13] percpu-rwsem: Optimize readers and reduce  global impact Oleg Nesterov <oleg@redhat.com> - 2015-06-23 01:10 +0200
    Re: [RFC][PATCH 05/13] percpu-rwsem: Optimize readers and reduce  global impact Tejun Heo <tj@kernel.org> - 2015-06-29 17:20 +0200
      Re: [RFC][PATCH 05/13] percpu-rwsem: Optimize readers and reduce  global impact Peter Zijlstra <peterz@infradead.org> - 2015-06-29 17:20 +0200
  [RFC][PATCH 11/13] fs/locks: Replace lg_local with a per-cpu spinlock Peter Zijlstra <peterz@infradead.org> - 2015-06-22 14:30 +0200
    Re: [RFC][PATCH 11/13] fs/locks: Replace lg_local with a per-cpu  spinlock Oleg Nesterov <oleg@redhat.com> - 2015-06-23 02:30 +0200
  [RFC][PATCH 10/13] fs/locks: Replace lg_global with a percpu-rwsem Peter Zijlstra <peterz@infradead.org> - 2015-06-22 14:30 +0200
  [RFC][PATCH 12/13] stop_machine: Remove lglock Peter Zijlstra <peterz@infradead.org> - 2015-06-22 14:30 +0200
    Re: [RFC][PATCH 12/13] stop_machine: Remove lglock Oleg Nesterov <oleg@redhat.com> - 2015-06-23 00:30 +0200
      Re: [RFC][PATCH 12/13] stop_machine: Remove lglock "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-06-24 04:30 +0200
        Re: [RFC][PATCH 12/13] stop_machine: Remove lglock Peter Zijlstra <peterz@infradead.org> - 2015-06-24 10:40 +0200
      Re: [RFC][PATCH 12/13] stop_machine: Remove lglock Peter Zijlstra <peterz@infradead.org> - 2015-06-24 09:40 +0200
        Re: [RFC][PATCH 12/13] stop_machine: Remove lglock Ingo Molnar <mingo@kernel.org> - 2015-06-24 10:50 +0200
  [RFC][PATCH 13/13] locking: Remove lglock Peter Zijlstra <peterz@infradead.org> - 2015-06-22 14:30 +0200
  [RFC][PATCH 03/13] rcusync: Add the CONFIG_PROVE_RCU checks Peter Zijlstra <peterz@infradead.org> - 2015-06-22 14:30 +0200
  [RFC][PATCH 07/13] sched: Reorder task_struct Peter Zijlstra <peterz@infradead.org> - 2015-06-22 14:30 +0200
  Re: [RFC][PATCH 00/13] percpu rwsem -v2 Peter Zijlstra <peterz@infradead.org> - 2015-06-22 14:40 +0200
  Re: [RFC][PATCH 00/13] percpu rwsem -v2 Linus Torvalds <torvalds@linux-foundation.org> - 2015-06-22 22:10 +0200
  Re: [RFC][PATCH 00/13] percpu rwsem -v2 Ingo Molnar <mingo@kernel.org> - 2015-06-24 10:50 +0200
    Re: [RFC][PATCH 00/13] percpu rwsem -v2 Peter Zijlstra <peterz@infradead.org> - 2015-06-24 11:10 +0200
    Re: [RFC][PATCH 00/13] percpu rwsem -v2 Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-06-24 11:20 +0200
      Re: [RFC][PATCH 00/13] percpu rwsem -v2 Linus Torvalds <torvalds@linux-foundation.org> - 2015-07-02 00:00 +0200
        Re: [RFC][PATCH 00/13] percpu rwsem -v2 Peter Zijlstra <peterz@infradead.org> - 2015-07-02 11:50 +0200

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