[PATCH v2 1/5] sched, timer: Remove usages of ACCESS_ONCE in the scheduler

Jason Low
2015-04-28T20:00:45Z

ACCESS_ONCE doesn't work reliably on non-scalar types. This patch removes
the rest of the existing usages of ACCESS_ONCE in the scheduler, and use
the new READ_ONCE and WRITE_ONCE APIs.

Signed-off-by: Jason Low <jason.low2@hp.com>
---
include/linux/sched.h | 4 ++--
kernel/fork.c | 2 +-
kernel/sched/auto_group.c | 2 +-
kernel/sched/auto_group.h | 2 +-
kernel/sched/core.c | 4 ++--
kernel/sched/cputime.c | 2 +-
kernel/sched/deadline.c | 2 +-
kernel/sched/fair.c | 14 +++++++-------
kernel/sched/proc.c | 4 ++--
kernel/sched/rt.c | 2 +-
kernel/sched/sched.h | 2 +-
kernel/sched/wait.c | 4 ++--
kernel/time/posix-cpu-timers.c | 8 ++++----
13 files changed, 26 insertions(+), 26 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8222ae4..604eb7c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -3088,13 +3088,13 @@ static inline void mm_update_next_owner(struct mm_struct *mm)
static inline unsigned long task_rlimit(const struct task_struct *tsk,
unsigned int limit)
{
- return ACCESS_ONCE(tsk->signal->rlim[limit].rlim_cur);
+ return READ_ONCE(tsk->signal->rlim[limit].rlim_cur);
}

static inline unsigned long task_rlimit_max(const struct task_struct *tsk,
unsigned int limit)
{
- return ACCESS_ONCE(tsk->signal->rlim[limit].rlim_max);
+ return READ_ONCE(tsk->signal->rlim[limit].rlim_max);
}

static inline unsigned long rlimit(unsigned int limit)
diff --git a/kernel/fork.c b/kernel/fork.c
index 03c1eaa..47c37a4 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1094,7 +1094,7 @@ static void posix_cpu_timers_init_group(struct signal_struct *sig)
/* Thread group counters. */
thread_group_cputime_init(sig);

- cpu_limit = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
+ cpu_limit = READ_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
if (cpu_limit != RLIM_INFINITY) {
sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
sig->cputimer.running = 1;
diff --git a/kernel/sched/auto_group.c b/kernel/sched/auto_group.c
index 1a3b58d..750ed60 100644
--- a/kernel/sched/auto_group.c
+++ b/kernel/sched/auto_group.c
@@ -139,7 +139,7 @@ autogroup_move_group(struct task_struct *p, struct autogroup *ag)

p->signal->autogroup = autogroup_kref_get(ag);

- if (!ACCESS_ONCE(sysctl_sched_autogroup_enabled))
+ if (!READ_ONCE(sysctl_sched_autogroup_enabled))
goto out;

for_each_thread(p, t)
diff --git a/kernel/sched/auto_group.h b/kernel/sched/auto_group.h
index 8bd0471..890c95f 100644
--- a/kernel/sched/auto_group.h
+++ b/kernel/sched/auto_group.h
@@ -29,7 +29,7 @@ extern bool task_wants_autogroup(struct task_struct *p, struct task_group *tg);
static inline struct task_group *
autogroup_task_group(struct task_struct *p, struct task_group *tg)
{
- int enabled = ACCESS_ONCE(sysctl_sched_autogroup_enabled);
+ int enabled = READ_ONCE(sysctl_sched_autogroup_enabled);

if (enabled && task_wants_autogroup(p, tg))
return p->signal->autogroup->tg;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f9123a8..aa88ff7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -511,7 +511,7 @@ static bool set_nr_and_not_polling(struct task_struct *p)
static bool set_nr_if_polling(struct task_struct *p)
{
struct thread_info *ti = task_thread_info(p);
- typeof(ti->flags) old, val = ACCESS_ONCE(ti->flags);
+ typeof(ti->flags) old, val = READ_ONCE(ti->flags);

for (;;) {
if (!(val & _TIF_POLLING_NRFLAG))
@@ -2540,7 +2540,7 @@ void scheduler_tick(void)
u64 scheduler_tick_max_deferment(void)
{
struct rq *rq = this_rq();
- unsigned long next, now = ACCESS_ONCE(jiffies);
+ unsigned long next, now = READ_ONCE(jiffies);

next = rq->last_sched_tick + HZ;

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 8394b1e..f5a64ff 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -567,7 +567,7 @@ static void cputime_advance(cputime_t *counter, cputime_t new)
{
cputime_t old;

- while (new > (old = ACCESS_ONCE(*counter)))
+ while (new > (old = READ_ONCE(*counter)))
cmpxchg_cputime(counter, old, new);
}

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 5e95145..890ce95 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -995,7 +995,7 @@ select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags)
rq = cpu_rq(cpu);

rcu_read_lock();
- curr = ACCESS_ONCE(rq->curr); /* unlocked access */
+ curr = READ_ONCE(rq->curr); /* unlocked access */

/*
* If we are dealing with a -deadline task, we must
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ffeaa41..5a44371 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -834,7 +834,7 @@ static unsigned int task_nr_scan_windows(struct task_struct *p)

static unsigned int task_scan_min(struct task_struct *p)
{
- unsigned int scan_size = ACCESS_ONCE(sysctl_numa_balancing_scan_size);
+ unsigned int scan_size = READ_ONCE(sysctl_numa_balancing_scan_size);
unsigned int scan, floor;
unsigned int windows = 1;

@@ -1794,7 +1794,7 @@ static void task_numa_placement(struct task_struct *p)
u64 runtime, period;
spinlock_t *group_lock = NULL;

- seq = ACCESS_ONCE(p->mm->numa_scan_seq);
+ seq = READ_ONCE(p->mm->numa_scan_seq);
if (p->numa_scan_seq == seq)
return;
p->numa_scan_seq = seq;
@@ -1938,7 +1938,7 @@ static void task_numa_group(struct task_struct *p, int cpupid, int flags,
}

rcu_read_lock();
- tsk = ACCESS_ONCE(cpu_rq(cpu)->curr);
+ tsk = READ_ONCE(cpu_rq(cpu)->curr);

if (!cpupid_match_pid(tsk, cpupid))
goto no_join;
@@ -2107,7 +2107,7 @@ void task_numa_fault(int last_cpupid, int mem_node, int pages, int flags)

static void reset_ptenuma_scan(struct task_struct *p)
{
- ACCESS_ONCE(p->mm->numa_scan_seq)++;
+ WRITE_ONCE(p->mm->numa_scan_seq, READ_ONCE(p->mm->numa_scan_seq) + 1);
p->mm->numa_scan_offset = 0;
}

@@ -4375,7 +4375,7 @@ static unsigned long capacity_orig_of(int cpu)
static unsigned long cpu_avg_load_per_task(int cpu)
{
struct rq *rq = cpu_rq(cpu);
- unsigned long nr_running = ACCESS_ONCE(rq->cfs.h_nr_running);
+ unsigned long nr_running = READ_ONCE(rq->cfs.h_nr_running);
unsigned long load_avg = rq->cfs.runnable_load_avg;

if (nr_running)
@@ -6037,8 +6037,8 @@ static unsigned long scale_rt_capacity(int cpu)
* Since we're reading these variables without serialization make sure
* we read them once before doing sanity checks on them.
*/
- age_stamp = ACCESS_ONCE(rq->age_stamp);
- avg = ACCESS_ONCE(rq->rt_avg);
+ age_stamp = READ_ONCE(rq->age_stamp);
+ avg = READ_ONCE(rq->rt_avg);
delta = __rq_clock_broken(rq) - age_stamp;

if (unlikely(delta < 0))
diff --git a/kernel/sched/proc.c b/kernel/sched/proc.c
index 8ecd552..361e6f1 100644
--- a/kernel/sched/proc.c
+++ b/kernel/sched/proc.c
@@ -526,7 +526,7 @@ static inline unsigned long get_rq_runnable_load(struct rq *rq)
*/
void update_idle_cpu_load(struct rq *this_rq)
{
- unsigned long curr_jiffies = ACCESS_ONCE(jiffies);
+ unsigned long curr_jiffies = READ_ONCE(jiffies);
unsigned long load = get_rq_runnable_load(this_rq);
unsigned long pending_updates;

@@ -548,7 +548,7 @@ void update_idle_cpu_load(struct rq *this_rq)
void update_cpu_load_nohz(void)
{
struct rq *this_rq = this_rq();
- unsigned long curr_jiffies = ACCESS_ONCE(jiffies);
+ unsigned long curr_jiffies = READ_ONCE(jiffies);
unsigned long pending_updates;

if (curr_jiffies == this_rq->last_load_update_tick)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 575da76..560d2fa 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1323,7 +1323,7 @@ select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags)
rq = cpu_rq(cpu);

rcu_read_lock();
- curr = ACCESS_ONCE(rq->curr); /* unlocked access */
+ curr = READ_ONCE(rq->curr); /* unlocked access */

/*
* If the current task on @p's runqueue is an RT task, then
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index e0e1299..014b550 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -707,7 +707,7 @@ DECLARE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);

static inline u64 __rq_clock_broken(struct rq *rq)
{
- return ACCESS_ONCE(rq->clock);
+ return READ_ONCE(rq->clock);
}

static inline u64 rq_clock(struct rq *rq)
diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
index 852143a..2ccec98 100644
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -601,7 +601,7 @@ EXPORT_SYMBOL(bit_wait_io);

__sched int bit_wait_timeout(struct wait_bit_key *word)
{
- unsigned long now = ACCESS_ONCE(jiffies);
+ unsigned long now = READ_ONCE(jiffies);
if (signal_pending_state(current->state, current))
return 1;
if (time_after_eq(now, word->timeout))
@@ -613,7 +613,7 @@ EXPORT_SYMBOL_GPL(bit_wait_timeout);

__sched int bit_wait_io_timeout(struct wait_bit_key *word)
{
- unsigned long now = ACCESS_ONCE(jiffies);
+ unsigned long now = READ_ONCE(jiffies);
if (signal_pending_state(current->state, current))
return 1;
if (time_after_eq(now, word->timeout))
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 0075da7..e072d98 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -852,10 +852,10 @@ static void check_thread_timers(struct task_struct *tsk,
/*
* Check for the special case thread timers.
*/
- soft = ACCESS_ONCE(sig->rlim[RLIMIT_RTTIME].rlim_cur);
+ soft = READ_ONCE(sig->rlim[RLIMIT_RTTIME].rlim_cur);
if (soft != RLIM_INFINITY) {
unsigned long hard =
- ACCESS_ONCE(sig->rlim[RLIMIT_RTTIME].rlim_max);
+ READ_ONCE(sig->rlim[RLIMIT_RTTIME].rlim_max);

if (hard != RLIM_INFINITY &&
tsk->rt.timeout > DIV_ROUND_UP(hard, USEC_PER_SEC/HZ)) {
@@ -958,11 +958,11 @@ static void check_process_timers(struct task_struct *tsk,
SIGPROF);
check_cpu_itimer(tsk, &sig->it[CPUCLOCK_VIRT], &virt_expires, utime,
SIGVTALRM);
- soft = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
+ soft = READ_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
if (soft != RLIM_INFINITY) {
unsigned long psecs = cputime_to_secs(ptime);
unsigned long hard =
- ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_max);
+ READ_ONCE(sig->rlim[RLIMIT_CPU].rlim_max);
cputime_t x;
if (psecs >= hard) {
/*
--
1.7.2.5