Revision 03049269de433cb5fe2859be9ae4469ceb1163ed authored by Michal Hocko on 25 March 2016, 21:20:33 UTC, committed by Linus Torvalds on 25 March 2016, 23:37:42 UTC
wake_oom_reaper has allowed only 1 oom victim to be queued. The main reason for that was the simplicity as other solutions would require some way of queuing. The current approach is racy and that was deemed sufficient as the oom_reaper is considered a best effort approach to help with oom handling when the OOM victim cannot terminate in a reasonable time. The race could lead to missing an oom victim which can get stuck out_of_memory wake_oom_reaper cmpxchg // OK oom_reaper oom_reap_task __oom_reap_task oom_victim terminates atomic_inc_not_zero // fail out_of_memory wake_oom_reaper cmpxchg // fails task_to_reap = NULL This race requires 2 OOM invocations in a short time period which is not very likely but certainly not impossible. E.g. the original victim might have not released a lot of memory for some reason. The situation would improve considerably if wake_oom_reaper used a more robust queuing. This is what this patch implements. This means adding oom_reaper_list list_head into task_struct (eat a hole before embeded thread_struct for that purpose) and a oom_reaper_lock spinlock for queuing synchronization. wake_oom_reaper will then add the task on the queue and oom_reaper will dequeue it. Signed-off-by: Michal Hocko <mhocko@suse.com> Cc: Vladimir Davydov <vdavydov@virtuozzo.com> Cc: Andrea Argangeli <andrea@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent bc448e8
irq_poll.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 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_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
{
/*
* If a CPU goes away, splice its entries to the current CPU
* and trigger a run of the softirq
*/
if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
int cpu = (unsigned long) hcpu;
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 NOTIFY_OK;
}
static struct notifier_block irq_poll_cpu_notifier = {
.notifier_call = irq_poll_cpu_notify,
};
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);
register_hotcpu_notifier(&irq_poll_cpu_notifier);
return 0;
}
subsys_initcall(irq_poll_setup);
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