Commit 8707d8b8 authored by Paul Menage's avatar Paul Menage Committed by Linus Torvalds

Fix cpusets update_cpumask

Cause writes to cpuset "cpus" file to update cpus_allowed for member tasks:

- collect batches of tasks under tasklist_lock and then call
  set_cpus_allowed() on them outside the lock (since this can sleep).

- add a simple generic priority heap type to allow efficient collection
  of batches of tasks to be processed without duplicating or missing any
  tasks in subsequent batches.

- make "cpus" file update a no-op if the mask hasn't changed

- fix race between update_cpumask() and sched_setaffinity() by making
  sched_setaffinity() post-check that it's not running on any cpus outside
  cpuset_cpus_allowed().

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: default avatarPaul Menage <menage@google.com>
Cc: Paul Jackson <pj@sgi.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 020958b6
#ifndef _LINUX_PRIO_HEAP_H
#define _LINUX_PRIO_HEAP_H
/*
* Simple insertion-only static-sized priority heap containing
* pointers, based on CLR, chapter 7
*/
#include <linux/gfp.h>
/**
* struct ptr_heap - simple static-sized priority heap
* @ptrs - pointer to data area
* @max - max number of elements that can be stored in @ptrs
* @size - current number of valid elements in @ptrs (in the range 0..@size-1
* @gt: comparison operator, which should implement "greater than"
*/
struct ptr_heap {
void **ptrs;
int max;
int size;
int (*gt)(void *, void *);
};
/**
* heap_init - initialize an empty heap with a given memory size
* @heap: the heap structure to be initialized
* @size: amount of memory to use in bytes
* @gfp_mask: mask to pass to kmalloc()
* @gt: comparison operator, which should implement "greater than"
*/
extern int heap_init(struct ptr_heap *heap, size_t size, gfp_t gfp_mask,
int (*gt)(void *, void *));
/**
* heap_free - release a heap's storage
* @heap: the heap structure whose data should be released
*/
void heap_free(struct ptr_heap *heap);
/**
* heap_insert - insert a value into the heap and return any overflowed value
* @heap: the heap to be operated on
* @p: the pointer to be inserted
*
* Attempts to insert the given value into the priority heap. If the
* heap is full prior to the insertion, then the resulting heap will
* consist of the smallest @max elements of the original heap and the
* new element; the greatest element will be removed from the heap and
* returned. Note that the returned element will be the new element
* (i.e. no change to the heap) if the new element is greater than all
* elements currently in the heap.
*/
extern void *heap_insert(struct ptr_heap *heap, void *p);
#endif /* _LINUX_PRIO_HEAP_H */
......@@ -38,6 +38,7 @@
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/pagemap.h>
#include <linux/prio_heap.h>
#include <linux/proc_fs.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
......@@ -701,6 +702,36 @@ done:
/* Don't kfree(doms) -- partition_sched_domains() does that. */
}
static inline int started_after_time(struct task_struct *t1,
struct timespec *time,
struct task_struct *t2)
{
int start_diff = timespec_compare(&t1->start_time, time);
if (start_diff > 0) {
return 1;
} else if (start_diff < 0) {
return 0;
} else {
/*
* Arbitrarily, if two processes started at the same
* time, we'll say that the lower pointer value
* started first. Note that t2 may have exited by now
* so this may not be a valid pointer any longer, but
* that's fine - it still serves to distinguish
* between two tasks started (effectively)
* simultaneously.
*/
return t1 > t2;
}
}
static inline int started_after(void *p1, void *p2)
{
struct task_struct *t1 = p1;
struct task_struct *t2 = p2;
return started_after_time(t1, &t2->start_time, t2);
}
/*
* Call with manage_mutex held. May take callback_mutex during call.
*/
......@@ -708,8 +739,15 @@ done:
static int update_cpumask(struct cpuset *cs, char *buf)
{
struct cpuset trialcs;
int retval;
int cpus_changed, is_load_balanced;
int retval, i;
int is_load_balanced;
struct cgroup_iter it;
struct cgroup *cgrp = cs->css.cgroup;
struct task_struct *p, *dropped;
/* Never dereference latest_task, since it's not refcounted */
struct task_struct *latest_task = NULL;
struct ptr_heap heap;
struct timespec latest_time = { 0, 0 };
/* top_cpuset.cpus_allowed tracks cpu_online_map; it's read-only */
if (cs == &top_cpuset)
......@@ -736,14 +774,73 @@ static int update_cpumask(struct cpuset *cs, char *buf)
if (retval < 0)
return retval;
cpus_changed = !cpus_equal(cs->cpus_allowed, trialcs.cpus_allowed);
/* Nothing to do if the cpus didn't change */
if (cpus_equal(cs->cpus_allowed, trialcs.cpus_allowed))
return 0;
retval = heap_init(&heap, PAGE_SIZE, GFP_KERNEL, &started_after);
if (retval)
return retval;
is_load_balanced = is_sched_load_balance(&trialcs);
mutex_lock(&callback_mutex);
cs->cpus_allowed = trialcs.cpus_allowed;
mutex_unlock(&callback_mutex);
if (cpus_changed && is_load_balanced)
again:
/*
* Scan tasks in the cpuset, and update the cpumasks of any
* that need an update. Since we can't call set_cpus_allowed()
* while holding tasklist_lock, gather tasks to be processed
* in a heap structure. If the statically-sized heap fills up,
* overflow tasks that started later, and in future iterations
* only consider tasks that started after the latest task in
* the previous pass. This guarantees forward progress and
* that we don't miss any tasks
*/
heap.size = 0;
cgroup_iter_start(cgrp, &it);
while ((p = cgroup_iter_next(cgrp, &it))) {
/* Only affect tasks that don't have the right cpus_allowed */
if (cpus_equal(p->cpus_allowed, cs->cpus_allowed))
continue;
/*
* Only process tasks that started after the last task
* we processed
*/
if (!started_after_time(p, &latest_time, latest_task))
continue;
dropped = heap_insert(&heap, p);
if (dropped == NULL) {
get_task_struct(p);
} else if (dropped != p) {
get_task_struct(p);
put_task_struct(dropped);
}
}
cgroup_iter_end(cgrp, &it);
if (heap.size) {
for (i = 0; i < heap.size; i++) {
struct task_struct *p = heap.ptrs[i];
if (i == 0) {
latest_time = p->start_time;
latest_task = p;
}
set_cpus_allowed(p, cs->cpus_allowed);
put_task_struct(p);
}
/*
* If we had to process any tasks at all, scan again
* in case some of them were in the middle of forking
* children that didn't notice the new cpumask
* restriction. Not the most efficient way to do it,
* but it avoids having to take callback_mutex in the
* fork path
*/
goto again;
}
heap_free(&heap);
if (is_load_balanced)
rebuild_sched_domains();
return 0;
......
......@@ -4471,8 +4471,21 @@ long sched_setaffinity(pid_t pid, cpumask_t new_mask)
cpus_allowed = cpuset_cpus_allowed(p);
cpus_and(new_mask, new_mask, cpus_allowed);
again:
retval = set_cpus_allowed(p, new_mask);
if (!retval) {
cpus_allowed = cpuset_cpus_allowed(p);
if (!cpus_subset(new_mask, cpus_allowed)) {
/*
* We must have raced with a concurrent cpuset
* update. Just reset the cpus_allowed to the
* cpuset's cpus_allowed
*/
new_mask = cpus_allowed;
goto again;
}
}
out_unlock:
put_task_struct(p);
mutex_unlock(&sched_hotcpu_mutex);
......
......@@ -6,7 +6,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
rbtree.o radix-tree.o dump_stack.o \
idr.o int_sqrt.o bitmap.o extable.o prio_tree.o \
sha1.o irq_regs.o reciprocal_div.o argv_split.o \
proportions.o
proportions.o prio_heap.o
lib-$(CONFIG_MMU) += ioremap.o
lib-$(CONFIG_SMP) += cpumask.o
......
/*
* Simple insertion-only static-sized priority heap containing
* pointers, based on CLR, chapter 7
*/
#include <linux/slab.h>
#include <linux/prio_heap.h>
int heap_init(struct ptr_heap *heap, size_t size, gfp_t gfp_mask,
int (*gt)(void *, void *))
{
heap->ptrs = kmalloc(size, gfp_mask);
if (!heap->ptrs)
return -ENOMEM;
heap->size = 0;
heap->max = size / sizeof(void *);
heap->gt = gt;
return 0;
}
void heap_free(struct ptr_heap *heap)
{
kfree(heap->ptrs);
}
void *heap_insert(struct ptr_heap *heap, void *p)
{
void *res;
void **ptrs = heap->ptrs;
int pos;
if (heap->size < heap->max) {
/* Heap insertion */
int pos = heap->size++;
while (pos > 0 && heap->gt(p, ptrs[(pos-1)/2])) {
ptrs[pos] = ptrs[(pos-1)/2];
pos = (pos-1)/2;
}
ptrs[pos] = p;
return NULL;
}
/* The heap is full, so something will have to be dropped */
/* If the new pointer is greater than the current max, drop it */
if (heap->gt(p, ptrs[0]))
return p;
/* Replace the current max and heapify */
res = ptrs[0];
ptrs[0] = p;
pos = 0;
while (1) {
int left = 2 * pos + 1;
int right = 2 * pos + 2;
int largest = pos;
if (left < heap->size && heap->gt(ptrs[left], p))
largest = left;
if (right < heap->size && heap->gt(ptrs[right], ptrs[largest]))
largest = right;
if (largest == pos)
break;
/* Push p down the heap one level and bump one up */
ptrs[pos] = ptrs[largest];
ptrs[largest] = p;
pos = largest;
}
return res;
}
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