linux/lib/irq_poll.c
Linus Torvalds 9ffc66941d This adds a new gcc plugin named "latent_entropy". It is designed to
extract as much possible uncertainty from a running system at boot time as
 possible, hoping to capitalize on any possible variation in CPU operation
 (due to runtime data differences, hardware differences, SMP ordering,
 thermal timing variation, cache behavior, etc).
 
 At the very least, this plugin is a much more comprehensive example for
 how to manipulate kernel code using the gcc plugin internals.
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Merge tag 'gcc-plugins-v4.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull gcc plugins update from Kees Cook:
 "This adds a new gcc plugin named "latent_entropy". It is designed to
  extract as much possible uncertainty from a running system at boot
  time as possible, hoping to capitalize on any possible variation in
  CPU operation (due to runtime data differences, hardware differences,
  SMP ordering, thermal timing variation, cache behavior, etc).

  At the very least, this plugin is a much more comprehensive example
  for how to manipulate kernel code using the gcc plugin internals"

* tag 'gcc-plugins-v4.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  latent_entropy: Mark functions with __latent_entropy
  gcc-plugins: Add latent_entropy plugin
2016-10-15 10:03:15 -07:00

215 lines
5.4 KiB
C

/*
* Functions related to interrupt-poll handling in the block layer. This
* is similar to NAPI for network devices.
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/bio.h>
#include <linux/interrupt.h>
#include <linux/cpu.h>
#include <linux/irq_poll.h>
#include <linux/delay.h>
static unsigned int irq_poll_budget __read_mostly = 256;
static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);
/**
* irq_poll_sched - Schedule a run of the iopoll handler
* @iop: The parent iopoll structure
*
* Description:
* Add this irq_poll structure to the pending poll list and trigger the
* raise of the blk iopoll softirq.
**/
void irq_poll_sched(struct irq_poll *iop)
{
unsigned long flags;
if (test_bit(IRQ_POLL_F_DISABLE, &iop->state))
return;
if (test_and_set_bit(IRQ_POLL_F_SCHED, &iop->state))
return;
local_irq_save(flags);
list_add_tail(&iop->list, this_cpu_ptr(&blk_cpu_iopoll));
__raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
local_irq_restore(flags);
}
EXPORT_SYMBOL(irq_poll_sched);
/**
* __irq_poll_complete - Mark this @iop as un-polled again
* @iop: The parent iopoll structure
*
* Description:
* See irq_poll_complete(). This function must be called with interrupts
* disabled.
**/
static void __irq_poll_complete(struct irq_poll *iop)
{
list_del(&iop->list);
smp_mb__before_atomic();
clear_bit_unlock(IRQ_POLL_F_SCHED, &iop->state);
}
/**
* irq_poll_complete - Mark this @iop as un-polled again
* @iop: The parent iopoll structure
*
* Description:
* If a driver consumes less than the assigned budget in its run of the
* iopoll handler, it'll end the polled mode by calling this function. The
* iopoll handler will not be invoked again before irq_poll_sched()
* is called.
**/
void irq_poll_complete(struct irq_poll *iop)
{
unsigned long flags;
local_irq_save(flags);
__irq_poll_complete(iop);
local_irq_restore(flags);
}
EXPORT_SYMBOL(irq_poll_complete);
static void __latent_entropy irq_poll_softirq(struct softirq_action *h)
{
struct list_head *list = this_cpu_ptr(&blk_cpu_iopoll);
int rearm = 0, budget = irq_poll_budget;
unsigned long start_time = jiffies;
local_irq_disable();
while (!list_empty(list)) {
struct irq_poll *iop;
int work, weight;
/*
* If softirq window is exhausted then punt.
*/
if (budget <= 0 || time_after(jiffies, start_time)) {
rearm = 1;
break;
}
local_irq_enable();
/* Even though interrupts have been re-enabled, this
* access is safe because interrupts can only add new
* entries to the tail of this list, and only ->poll()
* calls can remove this head entry from the list.
*/
iop = list_entry(list->next, struct irq_poll, list);
weight = iop->weight;
work = 0;
if (test_bit(IRQ_POLL_F_SCHED, &iop->state))
work = iop->poll(iop, weight);
budget -= work;
local_irq_disable();
/*
* Drivers must not modify the iopoll state, if they
* consume their assigned weight (or more, some drivers can't
* easily just stop processing, they have to complete an
* entire mask of commands).In such cases this code
* still "owns" the iopoll instance and therefore can
* move the instance around on the list at-will.
*/
if (work >= weight) {
if (test_bit(IRQ_POLL_F_DISABLE, &iop->state))
__irq_poll_complete(iop);
else
list_move_tail(&iop->list, list);
}
}
if (rearm)
__raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
local_irq_enable();
}
/**
* irq_poll_disable - Disable iopoll on this @iop
* @iop: The parent iopoll structure
*
* Description:
* Disable io polling and wait for any pending callbacks to have completed.
**/
void irq_poll_disable(struct irq_poll *iop)
{
set_bit(IRQ_POLL_F_DISABLE, &iop->state);
while (test_and_set_bit(IRQ_POLL_F_SCHED, &iop->state))
msleep(1);
clear_bit(IRQ_POLL_F_DISABLE, &iop->state);
}
EXPORT_SYMBOL(irq_poll_disable);
/**
* irq_poll_enable - Enable iopoll on this @iop
* @iop: The parent iopoll structure
*
* Description:
* Enable iopoll on this @iop. Note that the handler run will not be
* scheduled, it will only mark it as active.
**/
void irq_poll_enable(struct irq_poll *iop)
{
BUG_ON(!test_bit(IRQ_POLL_F_SCHED, &iop->state));
smp_mb__before_atomic();
clear_bit_unlock(IRQ_POLL_F_SCHED, &iop->state);
}
EXPORT_SYMBOL(irq_poll_enable);
/**
* irq_poll_init - Initialize this @iop
* @iop: The parent iopoll structure
* @weight: The default weight (or command completion budget)
* @poll_fn: The handler to invoke
*
* Description:
* Initialize and enable this irq_poll structure.
**/
void irq_poll_init(struct irq_poll *iop, int weight, irq_poll_fn *poll_fn)
{
memset(iop, 0, sizeof(*iop));
INIT_LIST_HEAD(&iop->list);
iop->weight = weight;
iop->poll = poll_fn;
}
EXPORT_SYMBOL(irq_poll_init);
static int irq_poll_cpu_dead(unsigned int cpu)
{
/*
* If a CPU goes away, splice its entries to the current CPU
* and trigger a run of the softirq
*/
local_irq_disable();
list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
this_cpu_ptr(&blk_cpu_iopoll));
__raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
local_irq_enable();
return 0;
}
static __init int irq_poll_setup(void)
{
int i;
for_each_possible_cpu(i)
INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i));
open_softirq(IRQ_POLL_SOFTIRQ, irq_poll_softirq);
cpuhp_setup_state_nocalls(CPUHP_IRQ_POLL_DEAD, "irq_poll:dead", NULL,
irq_poll_cpu_dead);
return 0;
}
subsys_initcall(irq_poll_setup);