[PATCH 4.19 25/32] sched/fair: Use RCU accessors consistently for ->numa_group

Greg Kroah-Hartman
2019-08-02T09:56:53Z

From: Jann Horn <jannh@google.com>

commit cb361d8cdef69990f6b4504dc1fd9a594d983c97 upstream.

The old code used RCU annotations and accessors inconsistently for
->numa_group, which can lead to use-after-frees and NULL dereferences.

Let all accesses to ->numa_group use proper RCU helpers to prevent such
issues.

Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Fixes: 8c8a743c5087 ("sched/numa: Use {cpu, pid} to create task groups for shared faults")
Link: https://lkml.kernel.org/r/20190716152047.14424-3-jannh@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/linux/sched.h | 10 +++-
kernel/sched/fair.c | 120 +++++++++++++++++++++++++++++++++-----------------
2 files changed, 90 insertions(+), 40 deletions(-)

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1023,7 +1023,15 @@ struct task_struct {
u64 last_sum_exec_runtime;
struct callback_head numa_work;

- struct numa_group *numa_group;
+ /*
+ * This pointer is only modified for current in syscall and
+ * pagefault context (and for tasks being destroyed), so it can be read
+ * from any of the following contexts:
+ * - RCU read-side critical section
+ * - current->numa_group from everywhere
+ * - task's runqueue locked, task not running
+ */
+ struct numa_group __rcu *numa_group;

/*
* numa_faults is an array split into four regions:
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1053,6 +1053,21 @@ struct numa_group {
unsigned long faults[0];
};

+/*
+ * For functions that can be called in multiple contexts that permit reading
+ * ->numa_group (see struct task_struct for locking rules).
+ */
+static struct numa_group *deref_task_numa_group(struct task_struct *p)
+{
+ return rcu_dereference_check(p->numa_group, p == current ||
+ (lockdep_is_held(&task_rq(p)->lock) && !READ_ONCE(p->on_cpu)));
+}
+
+static struct numa_group *deref_curr_numa_group(struct task_struct *p)
+{
+ return rcu_dereference_protected(p->numa_group, p == current);
+}
+
static inline unsigned long group_faults_priv(struct numa_group *ng);
static inline unsigned long group_faults_shared(struct numa_group *ng);

@@ -1096,10 +1111,12 @@ static unsigned int task_scan_start(stru
{
unsigned long smin = task_scan_min(p);
unsigned long period = smin;
+ struct numa_group *ng;

/* Scale the maximum scan period with the amount of shared memory. */
- if (p->numa_group) {
- struct numa_group *ng = p->numa_group;
+ rcu_read_lock();
+ ng = rcu_dereference(p->numa_group);
+ if (ng) {
unsigned long shared = group_faults_shared(ng);
unsigned long private = group_faults_priv(ng);

@@ -1107,6 +1124,7 @@ static unsigned int task_scan_start(stru
period *= shared + 1;
period /= private + shared + 1;
}
+ rcu_read_unlock();

return max(smin, period);
}
@@ -1115,13 +1133,14 @@ static unsigned int task_scan_max(struct
{
unsigned long smin = task_scan_min(p);
unsigned long smax;
+ struct numa_group *ng;

/* Watch for min being lower than max due to floor calculations */
smax = sysctl_numa_balancing_scan_period_max / task_nr_scan_windows(p);

/* Scale the maximum scan period with the amount of shared memory. */
- if (p->numa_group) {
- struct numa_group *ng = p->numa_group;
+ ng = deref_curr_numa_group(p);
+ if (ng) {
unsigned long shared = group_faults_shared(ng);
unsigned long private = group_faults_priv(ng);
unsigned long period = smax;
@@ -1153,7 +1172,7 @@ void init_numa_balancing(unsigned long c
p->numa_scan_period = sysctl_numa_balancing_scan_delay;
p->numa_work.next = &p->numa_work;
p->numa_faults = NULL;
- p->numa_group = NULL;
+ RCU_INIT_POINTER(p->numa_group, NULL);
p->last_task_numa_placement = 0;
p->last_sum_exec_runtime = 0;

@@ -1200,7 +1219,16 @@ static void account_numa_dequeue(struct

pid_t task_numa_group_id(struct task_struct *p)
{
- return p->numa_group ? p->numa_group->gid : 0;
+ struct numa_group *ng;
+ pid_t gid = 0;
+
+ rcu_read_lock();
+ ng = rcu_dereference(p->numa_group);
+ if (ng)
+ gid = ng->gid;
+ rcu_read_unlock();
+
+ return gid;
}

/*
@@ -1225,11 +1253,13 @@ static inline unsigned long task_faults(

static inline unsigned long group_faults(struct task_struct *p, int nid)
{
- if (!p->numa_group)
+ struct numa_group *ng = deref_task_numa_group(p);
+
+ if (!ng)
return 0;

- return p->numa_group->faults[task_faults_idx(NUMA_MEM, nid, 0)] +
- p->numa_group->faults[task_faults_idx(NUMA_MEM, nid, 1)];
+ return ng->faults[task_faults_idx(NUMA_MEM, nid, 0)] +
+ ng->faults[task_faults_idx(NUMA_MEM, nid, 1)];
}

static inline unsigned long group_faults_cpu(struct numa_group *group, int nid)
@@ -1367,12 +1397,13 @@ static inline unsigned long task_weight(
static inline unsigned long group_weight(struct task_struct *p, int nid,
int dist)
{
+ struct numa_group *ng = deref_task_numa_group(p);
unsigned long faults, total_faults;

- if (!p->numa_group)
+ if (!ng)
return 0;

- total_faults = p->numa_group->total_faults;
+ total_faults = ng->total_faults;

if (!total_faults)
return 0;
@@ -1386,7 +1417,7 @@ static inline unsigned long group_weight
bool should_numa_migrate_memory(struct task_struct *p, struct page * page,
int src_nid, int dst_cpu)
{
- struct numa_group *ng = p->numa_group;
+ struct numa_group *ng = deref_curr_numa_group(p);
int dst_nid = cpu_to_node(dst_cpu);
int last_cpupid, this_cpupid;

@@ -1592,13 +1623,14 @@ static bool load_too_imbalanced(long src
static void task_numa_compare(struct task_numa_env *env,
long taskimp, long groupimp, bool maymove)
{
+ struct numa_group *cur_ng, *p_ng = deref_curr_numa_group(env->p);
struct rq *dst_rq = cpu_rq(env->dst_cpu);
+ long imp = p_ng ? groupimp : taskimp;
struct task_struct *cur;
long src_load, dst_load;
- long load;
- long imp = env->p->numa_group ? groupimp : taskimp;
- long moveimp = imp;
int dist = env->dist;
+ long moveimp = imp;
+ long load;

if (READ_ONCE(dst_rq->numa_migrate_on))
return;
@@ -1637,21 +1669,22 @@ static void task_numa_compare(struct tas
* If dst and source tasks are in the same NUMA group, or not
* in any group then look only at task weights.
*/
- if (cur->numa_group == env->p->numa_group) {
+ cur_ng = rcu_dereference(cur->numa_group);
+ if (cur_ng == p_ng) {
imp = taskimp + task_weight(cur, env->src_nid, dist) -
task_weight(cur, env->dst_nid, dist);
/*
* Add some hysteresis to prevent swapping the
* tasks within a group over tiny differences.
*/
- if (cur->numa_group)
+ if (cur_ng)
imp -= imp / 16;
} else {
/*
* Compare the group weights. If a task is all by itself
* (not part of a group), use the task weight instead.
*/
- if (cur->numa_group && env->p->numa_group)
+ if (cur_ng && p_ng)
imp += group_weight(cur, env->src_nid, dist) -
group_weight(cur, env->dst_nid, dist);
else
@@ -1749,11 +1782,12 @@ static int task_numa_migrate(struct task
.best_imp = 0,
.best_cpu = -1,
};
+ unsigned long taskweight, groupweight;
struct sched_domain *sd;
+ long taskimp, groupimp;
+ struct numa_group *ng;
struct rq *best_rq;
- unsigned long taskweight, groupweight;
int nid, ret, dist;
- long taskimp, groupimp;

/*
* Pick the lowest SD_NUMA domain, as that would have the smallest
@@ -1799,7 +1833,8 @@ static int task_numa_migrate(struct task
* multiple NUMA nodes; in order to better consolidate the group,
* we need to check other locations.
*/
- if (env.best_cpu == -1 || (p->numa_group && p->numa_group->active_nodes > 1)) {
+ ng = deref_curr_numa_group(p);
+ if (env.best_cpu == -1 || (ng && ng->active_nodes > 1)) {
for_each_online_node(nid) {
if (nid == env.src_nid || nid == p->numa_preferred_nid)
continue;
@@ -1832,7 +1867,7 @@ static int task_numa_migrate(struct task
* A task that migrated to a second choice node will be better off
* trying for a better one later. Do not set the preferred node here.
*/
- if (p->numa_group) {
+ if (ng) {
if (env.best_cpu == -1)
nid = env.src_nid;
else
@@ -2127,6 +2162,7 @@ static void task_numa_placement(struct t
unsigned long total_faults;
u64 runtime, period;
spinlock_t *group_lock = NULL;
+ struct numa_group *ng;

/*
* The p->mm->numa_scan_seq field gets updated without
@@ -2144,8 +2180,9 @@ static void task_numa_placement(struct t
runtime = numa_get_avg_runtime(p, &period);

/* If the task is part of a group prevent parallel updates to group stats */
- if (p->numa_group) {
- group_lock = &p->numa_group->lock;
+ ng = deref_curr_numa_group(p);
+ if (ng) {
+ group_lock = &ng->lock;
spin_lock_irq(group_lock);
}

@@ -2186,7 +2223,7 @@ static void task_numa_placement(struct t
p->numa_faults[cpu_idx] += f_diff;
faults += p->numa_faults[mem_idx];
p->total_numa_faults += diff;
- if (p->numa_group) {
+ if (ng) {
/*
* safe because we can only change our own group
*
@@ -2194,14 +2231,14 @@ static void task_numa_placement(struct t
* nid and priv in a specific region because it
* is at the beginning of the numa_faults array.
*/
- p->numa_group->faults[mem_idx] += diff;
- p->numa_group->faults_cpu[mem_idx] += f_diff;
- p->numa_group->total_faults += diff;
- group_faults += p->numa_group->faults[mem_idx];
+ ng->faults[mem_idx] += diff;
+ ng->faults_cpu[mem_idx] += f_diff;
+ ng->total_faults += diff;
+ group_faults += ng->faults[mem_idx];
}
}

- if (!p->numa_group) {
+ if (!ng) {
if (faults > max_faults) {
max_faults = faults;
max_nid = nid;
@@ -2212,8 +2249,8 @@ static void task_numa_placement(struct t
}
}

- if (p->numa_group) {
- numa_group_count_active_nodes(p->numa_group);
+ if (ng) {
+ numa_group_count_active_nodes(ng);
spin_unlock_irq(group_lock);
max_nid = preferred_group_nid(p, max_nid);
}
@@ -2247,7 +2284,7 @@ static void task_numa_group(struct task_
int cpu = cpupid_to_cpu(cpupid);
int i;

- if (unlikely(!p->numa_group)) {
+ if (unlikely(!deref_curr_numa_group(p))) {
unsigned int size = sizeof(struct numa_group) +
4*nr_node_ids*sizeof(unsigned long);

@@ -2283,7 +2320,7 @@ static void task_numa_group(struct task_
if (!grp)
goto no_join;

- my_grp = p->numa_group;
+ my_grp = deref_curr_numa_group(p);
if (grp == my_grp)
goto no_join;

@@ -2354,7 +2391,8 @@ no_join:
*/
void task_numa_free(struct task_struct *p, bool final)
{
- struct numa_group *grp = p->numa_group;
+ /* safe: p either is current or is being freed by current */
+ struct numa_group *grp = rcu_dereference_raw(p->numa_group);
unsigned long *numa_faults = p->numa_faults;
unsigned long flags;
int i;
@@ -2434,7 +2472,7 @@ void task_numa_fault(int last_cpupid, in
* actively using should be counted as local. This allows the
* scan rate to slow down when a workload has settled down.
*/
- ng = p->numa_group;
+ ng = deref_curr_numa_group(p);
if (!priv && !local && ng && ng->active_nodes > 1 &&
numa_is_active_node(cpu_node, ng) &&
numa_is_active_node(mem_node, ng))
@@ -10234,18 +10272,22 @@ void show_numa_stats(struct task_struct
{
int node;
unsigned long tsf = 0, tpf = 0, gsf = 0, gpf = 0;
+ struct numa_group *ng;

+ rcu_read_lock();
+ ng = rcu_dereference(p->numa_group);
for_each_online_node(node) {
if (p->numa_faults) {
tsf = p->numa_faults[task_faults_idx(NUMA_MEM, node, 0)];
tpf = p->numa_faults[task_faults_idx(NUMA_MEM, node, 1)];
}
- if (p->numa_group) {
- gsf = p->numa_group->faults[task_faults_idx(NUMA_MEM, node, 0)],
- gpf = p->numa_group->faults[task_faults_idx(NUMA_MEM, node, 1)];
+ if (ng) {
+ gsf = ng->faults[task_faults_idx(NUMA_MEM, node, 0)],
+ gpf = ng->faults[task_faults_idx(NUMA_MEM, node, 1)];
}
print_numa_stats(m, node, tsf, tpf, gsf, gpf);
}
+ rcu_read_unlock();
}
#endif /* CONFIG_NUMA_BALANCING */
#endif /* CONFIG_SCHED_DEBUG */