Re: [PATCH] omit POSIX timer stuff from task_struct when disabled

From: Nicolas Pitre
Date: Sat Jan 21 2017 - 01:21:01 EST

On Fri, 20 Jan 2017, John Stultz wrote:

> On Fri, Jan 20, 2017 at 2:46 PM, Nicolas Pitre <nicolas.pitre@xxxxxxxxxx> wrote:
> > Just tell me if you prefer that I respin the patch and I'll do it.
>
> Yea. I'm not so finicky but I'm sure I'll probably get yelled at if I
> pass it on, so if you don't mind respinning it, I'll get it applied
> for testing here quickly :)

There you go.

----- >8
Subject: omit POSIX timer stuff from task_struct when disabled

When CONFIG_POSIX_TIMERS is disabled, it is preferable to remove related
structures from struct task_struct and struct signal_struct as they
won't contain anything useful and shouldn't be relied upon by mistake.
Code still referencing those structures is also disabled here.

Signed-off-by: Nicolas Pitre <nico@xxxxxxxxxx>

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 8e7e61b28f..03deeac1e8 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2179,7 +2179,7 @@ static const struct file_operations proc_map_files_operations = {
.llseek = generic_file_llseek,
};

-#ifdef CONFIG_CHECKPOINT_RESTORE
+#if defined(CONFIG_CHECKPOINT_RESTORE) && defined(CONFIG_POSIX_TIMERS)
struct timers_private {
struct pid *pid;
struct task_struct *task;
@@ -2936,7 +2936,7 @@ static const struct pid_entry tgid_base_stuff[] = {
REG("projid_map", S_IRUGO|S_IWUSR, proc_projid_map_operations),
REG("setgroups", S_IRUGO|S_IWUSR, proc_setgroups_operations),
#endif
-#ifdef CONFIG_CHECKPOINT_RESTORE
+#if defined(CONFIG_CHECKPOINT_RESTORE) && defined(CONFIG_POSIX_TIMERS)
REG("timers", S_IRUGO, proc_timers_operations),
#endif
REG("timerslack_ns", S_IRUGO|S_IWUGO, proc_pid_set_timerslack_ns_operations),
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 325f649d77..3a85d61f76 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -42,6 +42,27 @@ extern struct fs_struct init_fs;
#define INIT_PREV_CPUTIME(x)
#endif

+#ifdef CONFIG_POSIX_TIMERS
+#define INIT_POSIX_TIMERS(s) \
+ .posix_timers = LIST_HEAD_INIT(s.posix_timers),
+#define INIT_CPU_TIMERS(s) \
+ .cpu_timers = { \
+ LIST_HEAD_INIT(s.cpu_timers[0]), \
+ LIST_HEAD_INIT(s.cpu_timers[1]), \
+ LIST_HEAD_INIT(s.cpu_timers[2]), \
+ },
+#define INIT_CPUTIMER(s) \
+ .cputimer = { \
+ .cputime_atomic = INIT_CPUTIME_ATOMIC, \
+ .running = false, \
+ .checking_timer = false, \
+ },
+#else
+#define INIT_POSIX_TIMERS(s)
+#define INIT_CPU_TIMERS(s)
+#define INIT_CPUTIMER(s)
+#endif
+
#define INIT_SIGNALS(sig) { \
.nr_threads = 1, \
.thread_head = LIST_HEAD_INIT(init_task.thread_node), \
@@ -49,14 +70,10 @@ extern struct fs_struct init_fs;
.shared_pending = { \
.list = LIST_HEAD_INIT(sig.shared_pending.list), \
.signal = {{0}}}, \
- .posix_timers = LIST_HEAD_INIT(sig.posix_timers), \
- .cpu_timers = INIT_CPU_TIMERS(sig.cpu_timers), \
+ INIT_POSIX_TIMERS(sig) \
+ INIT_CPU_TIMERS(sig) \
.rlim = INIT_RLIMITS, \
- .cputimer = { \
- .cputime_atomic = INIT_CPUTIME_ATOMIC, \
- .running = false, \
- .checking_timer = false, \
- }, \
+ INIT_CPUTIMER(sig) \
INIT_PREV_CPUTIME(sig) \
.cred_guard_mutex = \
__MUTEX_INITIALIZER(sig.cred_guard_mutex), \
@@ -247,7 +264,7 @@ extern struct task_group root_task_group;
.blocked = {{0}}, \
.alloc_lock = __SPIN_LOCK_UNLOCKED(tsk.alloc_lock), \
.journal_info = NULL, \
- .cpu_timers = INIT_CPU_TIMERS(tsk.cpu_timers), \
+ INIT_CPU_TIMERS(tsk) \
.pi_lock = __RAW_SPIN_LOCK_UNLOCKED(tsk.pi_lock), \
.timer_slack_ns = 50000, /* 50 usec default slack */ \
.pids = { \
@@ -274,13 +291,6 @@ extern struct task_group root_task_group;
}


-#define INIT_CPU_TIMERS(cpu_timers) \
-{ \
- LIST_HEAD_INIT(cpu_timers[0]), \
- LIST_HEAD_INIT(cpu_timers[1]), \
- LIST_HEAD_INIT(cpu_timers[2]), \
-}
-
/* Attach to the init_task data structure for proper alignment */
#define __init_task_data __attribute__((__section__(".data..init_task")))

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4d1905245c..e8f6af5972 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -734,13 +734,14 @@ struct signal_struct {
unsigned int is_child_subreaper:1;
unsigned int has_child_subreaper:1;

+#ifdef CONFIG_POSIX_TIMERS
+
/* POSIX.1b Interval Timers */
int posix_timer_id;
struct list_head posix_timers;

/* ITIMER_REAL timer for the process */
struct hrtimer real_timer;
- struct pid *leader_pid;
ktime_t it_real_incr;

/*
@@ -759,12 +760,16 @@ struct signal_struct {
/* Earliest-expiration cache. */
struct task_cputime cputime_expires;

+ struct list_head cpu_timers[3];
+
+#endif
+
+ struct pid *leader_pid;
+
#ifdef CONFIG_NO_HZ_FULL
atomic_t tick_dep_mask;
#endif

- struct list_head cpu_timers[3];
-
struct pid *tty_old_pgrp;

/* boolean value for session group leader */
@@ -1681,8 +1686,10 @@ struct task_struct {
/* mm fault and swap info: this can arguably be seen as either mm-specific or thread-specific */
unsigned long min_flt, maj_flt;

+#ifdef CONFIG_POSIX_TIMERS
struct task_cputime cputime_expires;
struct list_head cpu_timers[3];
+#endif

/* process credentials */
const struct cred __rcu *ptracer_cred; /* Tracer's credentials at attach */
diff --git a/kernel/fork.c b/kernel/fork.c
index 11c5c8ab82..105c6676d9 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1304,6 +1304,7 @@ void __cleanup_sighand(struct sighand_struct *sighand)
}
}

+#ifdef CONFIG_POSIX_TIMERS
/*
* Initialize POSIX timer handling for a thread group.
*/
@@ -1322,6 +1323,9 @@ static void posix_cpu_timers_init_group(struct signal_struct *sig)
INIT_LIST_HEAD(&sig->cpu_timers[1]);
INIT_LIST_HEAD(&sig->cpu_timers[2]);
}
+#else
+static inline void posix_cpu_timers_init_group(struct signal_struct *sig) { }
+#endif

static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
{
@@ -1346,11 +1350,11 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
init_waitqueue_head(&sig->wait_chldexit);
sig->curr_target = tsk;
init_sigpending(&sig->shared_pending);
- INIT_LIST_HEAD(&sig->posix_timers);
seqlock_init(&sig->stats_lock);
prev_cputime_init(&sig->prev_cputime);

#ifdef CONFIG_POSIX_TIMERS
+ INIT_LIST_HEAD(&sig->posix_timers);
hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
sig->real_timer.function = it_real_fn;
#endif
@@ -1425,6 +1429,7 @@ static void rt_mutex_init_task(struct task_struct *p)
#endif
}

+#ifdef CONFIG_POSIX_TIMERS
/*
* Initialize POSIX timer handling for a single task.
*/
@@ -1437,6 +1442,9 @@ static void posix_cpu_timers_init(struct task_struct *tsk)
INIT_LIST_HEAD(&tsk->cpu_timers[1]);
INIT_LIST_HEAD(&tsk->cpu_timers[2]);
}
+#else
+static inline void posix_cpu_timers_init(struct task_struct *tsk) { }
+#endif

static inline void
init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 2516b8df6d..a688a82067 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2246,6 +2246,7 @@ prio_changed_rt(struct rq *rq, struct task_struct *p, int oldprio)
}
}

+#ifdef CONFIG_POSIX_TIMERS
static void watchdog(struct rq *rq, struct task_struct *p)
{
unsigned long soft, hard;
@@ -2267,6 +2268,9 @@ static void watchdog(struct rq *rq, struct task_struct *p)
p->cputime_expires.sched_exp = p->se.sum_exec_runtime;
}
}
+#else
+static inline void watchdog(struct rq *rq, struct task_struct *p) { }
+#endif

static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
{
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index 34659a8535..c69a9870ab 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -172,18 +172,19 @@ sched_info_switch(struct rq *rq,
*/

/**
- * cputimer_running - return true if cputimer is running
+ * get_running_cputimer - return &tsk->signal->cputimer if cputimer is running
*
* @tsk: Pointer to target task.
*/
-static inline bool cputimer_running(struct task_struct *tsk)
-
+#ifdef CONFIG_POSIX_TIMERS
+static inline
+struct thread_group_cputimer *get_running_cputimer(struct task_struct *tsk)
{
struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;

/* Check if cputimer isn't running. This is accessed without locking. */
if (!READ_ONCE(cputimer->running))
- return false;
+ return NULL;

/*
* After we flush the task's sum_exec_runtime to sig->sum_sched_runtime
@@ -200,10 +201,17 @@ static inline bool cputimer_running(struct task_struct *tsk)
* clock delta is behind the expiring timer value.
*/
if (unlikely(!tsk->sighand))
- return false;
+ return NULL;

- return true;
+ return cputimer;
+}
+#else
+static inline
+struct thread_group_cputimer *get_running_cputimer(struct task_struct *tsk)
+{
+ return NULL;
}
+#endif

/**
* account_group_user_time - Maintain utime for a thread group.
@@ -218,9 +226,9 @@ static inline bool cputimer_running(struct task_struct *tsk)
static inline void account_group_user_time(struct task_struct *tsk,
cputime_t cputime)
{
- struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
+ struct thread_group_cputimer *cputimer = get_running_cputimer(tsk);

- if (!cputimer_running(tsk))
+ if (!cputimer)
return;

atomic64_add(cputime, &cputimer->cputime_atomic.utime);
@@ -239,9 +247,9 @@ static inline void account_group_user_time(struct task_struct *tsk,
static inline void account_group_system_time(struct task_struct *tsk,
cputime_t cputime)
{
- struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
+ struct thread_group_cputimer *cputimer = get_running_cputimer(tsk);

- if (!cputimer_running(tsk))
+ if (!cputimer)
return;

atomic64_add(cputime, &cputimer->cputime_atomic.stime);
@@ -260,9 +268,9 @@ static inline void account_group_system_time(struct task_struct *tsk,
static inline void account_group_exec_runtime(struct task_struct *tsk,
unsigned long long ns)
{
- struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
+ struct thread_group_cputimer *cputimer = get_running_cputimer(tsk);

- if (!cputimer_running(tsk))
+ if (!cputimer)
return;

atomic64_add(ns, &cputimer->cputime_atomic.sum_exec_runtime);