1. 07 Jun, 2014 1 commit
  2. 04 Feb, 2013 1 commit
  3. 18 Nov, 2012 1 commit
    • Frederic Weisbecker's avatar
      irq_work: Make self-IPIs optable · bc6679ae
      Frederic Weisbecker authored
      On irq work initialization, let the user choose to define it
      as "lazy" or not. "Lazy" means that we don't want to send
      an IPI (provided the arch can anyway) when we enqueue this
      work but we rather prefer to wait for the next timer tick
      to execute our work if possible.
      
      This is going to be a benefit for non-urgent enqueuers
      (like printk in the future) that may prefer not to raise
      an IPI storm in case of frequent enqueuing on short periods
      of time.
      Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
      Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
      bc6679ae
  4. 17 Nov, 2012 3 commits
    • Steven Rostedt's avatar
      irq_work: Warn if there's still work on cpu_down · 8aa2acce
      Steven Rostedt authored
      If we are in nohz and there's still irq_work to be done when the idle
      task is about to go offline, give a nasty warning. Everything should
      have been flushed from the CPU_DYING notifier already. Further attempts
      to enqueue an irq_work are buggy because irqs are disabled by
      __cpu_disable(). The best we can do is to report the issue to the user.
      Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
      Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
      8aa2acce
    • Steven Rostedt's avatar
      irq_work: Flush work on CPU_DYING · c0e980a4
      Steven Rostedt authored
      In order not to offline a CPU with pending irq works, flush the
      queue from CPU_DYING. The notifier is called by stop_machine on
      the CPU that is going down. The code will not be called from irq context
      (so things like get_irq_regs() wont work) but I'm not sure what the
      requirements are for irq_work in that regard (Peter?). But irqs are
      disabled and the CPU is about to go offline. Might as well flush the work.
      Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
      Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
      c0e980a4
    • Frederic Weisbecker's avatar
      irq_work: Don't stop the tick with pending works · 00b42959
      Frederic Weisbecker authored
      Don't stop the tick if we have pending irq works on the
      queue, otherwise if the arch can't raise self-IPIs, we may not
      find an opportunity to execute the pending works for a while.
      Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
      Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
      00b42959
  5. 14 Nov, 2012 2 commits
    • Frederic Weisbecker's avatar
      irq_work: Fix racy check on work pending flag · e0bbe2d8
      Frederic Weisbecker authored
      Work claiming wants to be SMP-safe.
      
      And by the time we try to claim a work, if it is already executing
      concurrently on another CPU, we want to succeed the claiming and queue
      the work again because the other CPU may have missed the data we wanted
      to handle in our work if it's about to complete there.
      
      This scenario is summarized below:
      
              CPU 1                                   CPU 2
              -----                                   -----
              (flags = 0)
              cmpxchg(flags, 0, IRQ_WORK_FLAGS)
              (flags = 3)
              [...]
              xchg(flags, IRQ_WORK_BUSY)
              (flags = 2)
              func()
                                                      if (flags & IRQ_WORK_PENDING)
                                                              (not true)
                                                      cmpxchg(flags, flags, IRQ_WORK_FLAGS)
                                                      (flags = 3)
                                                      [...]
              cmpxchg(flags, IRQ_WORK_BUSY, 0);
              (fail, pending on CPU 2)
      
      This state machine is synchronized using [cmp]xchg() on the flags.
      As such, the early IRQ_WORK_PENDING check in CPU 2 above is racy.
      By the time we check it, we may be dealing with a stale value because
      we aren't using an atomic accessor. As a result, CPU 2 may "see"
      that the work is still pending on another CPU while it may be
      actually completing the work function exection already, leaving
      our data unprocessed.
      
      To fix this, we start by speculating about the value we wish to be
      in the work->flags but we only make any conclusion after the value
      returned by the cmpxchg() call that either claims the work or let
      the current owner handle the pending work for us.
      Changelog-heavily-inspired-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
      Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
      Cc: Anish Kumar <anish198519851985@gmail.com>
      e0bbe2d8
    • Frederic Weisbecker's avatar
      irq_work: Fix racy IRQ_WORK_BUSY flag setting · c8446b75
      Frederic Weisbecker authored
      The IRQ_WORK_BUSY flag is set right before we execute the
      work. Once this flag value is set, the work enters a
      claimable state again.
      
      So if we have specific data to compute in our work, we ensure it's
      either handled by another CPU or locally by enqueuing the work again.
      This state machine is guanranteed by atomic operations on the flags.
      
      So when we set IRQ_WORK_BUSY without using an xchg-like operation,
      we break this guarantee as in the following summarized scenario:
      
              CPU 1                                   CPU 2
              -----                                   -----
                                                      (flags = 0)
                                                      old_flags = flags;
              (flags = 0)
              cmpxchg(flags, old_flags,
                      old_flags | IRQ_WORK_FLAGS)
              (flags = 3)
              [...]
              flags = IRQ_WORK_BUSY
              (flags = 2)
              func()
                                                      (sees flags = 3)
                                                      cmpxchg(flags, old_flags,
                                                              old_flags | IRQ_WORK_FLAGS)
                                                      (give up)
      
              cmpxchg(flags, 2, 0);
              (flags = 0)
      
      CPU 1 claims a work and executes it, so it sets IRQ_WORK_BUSY and
      the work is again in a claimable state. Now CPU 2 has new data to process
      and try to claim that work but it may see a stale value of the flags
      and think the work is still pending somewhere that will handle our data.
      This is because CPU 1 doesn't set IRQ_WORK_BUSY atomically.
      
      As a result, the data expected to be handle by CPU 2 won't get handled.
      
      To fix this, use xchg() to set IRQ_WORK_BUSY, this way we ensure the CPU 2
      will see the correct value with cmpxchg() using the expected ordering.
      Changelog-heavily-inspired-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
      Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
      Cc: Anish Kumar <anish198519851985@gmail.com>
      c8446b75
  6. 13 Apr, 2012 1 commit
  7. 02 Apr, 2012 1 commit
  8. 31 Oct, 2011 2 commits
    • Paul Gortmaker's avatar
      kernel: fix two implicit header assumptions in irq_work.c · 967d1f90
      Paul Gortmaker authored
      Up until now, this file was getting percpu.h because nearly every
      file was implicitly getting module.h (and all its sub-includes).
      But we want to clean that up, so call out percpu.h explicitly.
      Otherwise we'll get things like this on an ARM build:
      
      kernel/irq_work.c:48: error: expected declaration specifiers or '...' before 'irq_work_list'
      kernel/irq_work.c:48: warning: type defaults to 'int' in declaration of 'DEFINE_PER_CPU'
      
      The same thing was happening for builds on ARM for asm/processor.h
      
      kernel/irq_work.c: In function 'irq_work_sync':
      kernel/irq_work.c:166: error: implicit declaration of function 'cpu_relax'
      Signed-off-by: default avatarPaul Gortmaker <paul.gortmaker@windriver.com>
      967d1f90
    • Paul Gortmaker's avatar
      kernel: Map most files to use export.h instead of module.h · 9984de1a
      Paul Gortmaker authored
      The changed files were only including linux/module.h for the
      EXPORT_SYMBOL infrastructure, and nothing else.  Revector them
      onto the isolated export header for faster compile times.
      
      Nothing to see here but a whole lot of instances of:
      
        -#include <linux/module.h>
        +#include <linux/export.h>
      
      This commit is only changing the kernel dir; next targets
      will probably be mm, fs, the arch dirs, etc.
      Signed-off-by: default avatarPaul Gortmaker <paul.gortmaker@windriver.com>
      9984de1a
  9. 04 Oct, 2011 2 commits
  10. 18 Dec, 2010 1 commit
    • Christoph Lameter's avatar
      irq_work: Use per cpu atomics instead of regular atomics · 20b87691
      Christoph Lameter authored
      The irq work queue is a per cpu object and it is sufficient for
      synchronization if per cpu atomics are used. Doing so simplifies
      the code and reduces the overhead of the code.
      
      Before:
      
      christoph@linux-2.6$ size kernel/irq_work.o
         text	   data	    bss	    dec	    hex	filename
          451	      8	      1	    460	    1cc	kernel/irq_work.o
      
      After:
      
      christoph@linux-2.6$ size kernel/irq_work.o 
         text	   data	    bss	    dec	    hex	filename
          438	      8	      1	    447	    1bf	kernel/irq_work.o
      
      Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
      Signed-off-by: default avatarChristoph Lameter <cl@linux.com>
      20b87691
  11. 18 Nov, 2010 1 commit
  12. 18 Oct, 2010 1 commit
    • Peter Zijlstra's avatar
      irq_work: Add generic hardirq context callbacks · e360adbe
      Peter Zijlstra authored
      Provide a mechanism that allows running code in IRQ context. It is
      most useful for NMI code that needs to interact with the rest of the
      system -- like wakeup a task to drain buffers.
      
      Perf currently has such a mechanism, so extract that and provide it as
      a generic feature, independent of perf so that others may also
      benefit.
      
      The IRQ context callback is generated through self-IPIs where
      possible, or on architectures like powerpc the decrementer (the
      built-in timer facility) is set to generate an interrupt immediately.
      
      Architectures that don't have anything like this get to do with a
      callback from the timer tick. These architectures can call
      irq_work_run() at the tail of any IRQ handlers that might enqueue such
      work (like the perf IRQ handler) to avoid undue latencies in
      processing the work.
      Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
      Acked-by: default avatarKyle McMartin <kyle@mcmartin.ca>
      Acked-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
      [ various fixes ]
      Signed-off-by: default avatarHuang Ying <ying.huang@intel.com>
      LKML-Reference: <1287036094.7768.291.camel@yhuang-dev>
      Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      e360adbe