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Commit 0e6601ee authored by Ingo Molnar's avatar Ingo Molnar
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Merge branch 'timers/posix-timers-for-tip-v2' of... 

Merge branch 'timers/posix-timers-for-tip-v2' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks into timers/core

Pull posix cpu timer changes for v3.14 from Frederic Weisbecker:

 * Remove dying thread/process timers caching that was complicating the code
   for no significant win.

 * Remove early task reference release on dying timer sample read. Again it was
   not worth the code complication. The other timer's resources aren't released
   until timer_delete() is called anyway (or when the whole process dies).

 * Remove leftover arguments in reaped target cleanup

 * Consolidate some timer sampling code

 * Remove use of tasklist lock

 * Robustify sighand locking against exec and exit by using the safer
   lock_task_sighand() API instead of sighand raw locking.

 * Convert some unnecessary BUG_ON() to WARN_ON()
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parents a934a56e 531f64fd
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Showing with 129 additions and 183 deletions
kernel/posix-cpu-timers.c
View file @ 0e6601ee
......@@ -233,7 +233,8 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
/*
* Sample a process (thread group) clock for the given group_leader task.
* Must be called with tasklist_lock held for reading.
* Must be called with task sighand lock held for safe while_each_thread()
* traversal.
*/
static int cpu_clock_sample_group(const clockid_t which_clock,
struct task_struct *p,
......@@ -260,30 +261,53 @@ static int cpu_clock_sample_group(const clockid_t which_clock,
return 0;
}
static int posix_cpu_clock_get_task(struct task_struct *tsk,
const clockid_t which_clock,
struct timespec *tp)
{
int err = -EINVAL;
unsigned long long rtn;
if (CPUCLOCK_PERTHREAD(which_clock)) {
if (same_thread_group(tsk, current))
err = cpu_clock_sample(which_clock, tsk, &rtn);
} else {
unsigned long flags;
struct sighand_struct *sighand;
/*
* while_each_thread() is not yet entirely RCU safe,
* keep locking the group while sampling process
* clock for now.
*/
sighand = lock_task_sighand(tsk, &flags);
if (!sighand)
return err;
if (tsk == current || thread_group_leader(tsk))
err = cpu_clock_sample_group(which_clock, tsk, &rtn);
unlock_task_sighand(tsk, &flags);
}
if (!err)
sample_to_timespec(which_clock, rtn, tp);
return err;
}
static int posix_cpu_clock_get(const clockid_t which_clock, struct timespec *tp)
{
const pid_t pid = CPUCLOCK_PID(which_clock);
int error = -EINVAL;
unsigned long long rtn;
int err = -EINVAL;
if (pid == 0) {
/*
* Special case constant value for our own clocks.
* We don't have to do any lookup to find ourselves.
*/
if (CPUCLOCK_PERTHREAD(which_clock)) {
/*
* Sampling just ourselves we can do with no locking.
*/
error = cpu_clock_sample(which_clock,
current, &rtn);
} else {
read_lock(&tasklist_lock);
error = cpu_clock_sample_group(which_clock,
current, &rtn);
read_unlock(&tasklist_lock);
}
err = posix_cpu_clock_get_task(current, which_clock, tp);
} else {
/*
* Find the given PID, and validate that the caller
......@@ -292,29 +316,12 @@ static int posix_cpu_clock_get(const clockid_t which_clock, struct timespec *tp)
struct task_struct *p;
rcu_read_lock();
p = find_task_by_vpid(pid);
if (p) {
if (CPUCLOCK_PERTHREAD(which_clock)) {
if (same_thread_group(p, current)) {
error = cpu_clock_sample(which_clock,
p, &rtn);
}
} else {
read_lock(&tasklist_lock);
if (thread_group_leader(p) && p->sighand) {
error =
cpu_clock_sample_group(which_clock,
p, &rtn);
}
read_unlock(&tasklist_lock);
}
}
if (p)
err = posix_cpu_clock_get_task(p, which_clock, tp);
rcu_read_unlock();
}
if (error)
return error;
sample_to_timespec(which_clock, rtn, tp);
return 0;
return err;
}
......@@ -371,36 +378,40 @@ static int posix_cpu_timer_create(struct k_itimer *new_timer)
*/
static int posix_cpu_timer_del(struct k_itimer *timer)
{
struct task_struct *p = timer->it.cpu.task;
int ret = 0;
unsigned long flags;
struct sighand_struct *sighand;
struct task_struct *p = timer->it.cpu.task;
if (likely(p != NULL)) {
read_lock(&tasklist_lock);
if (unlikely(p->sighand == NULL)) {
/*
* We raced with the reaping of the task.
* The deletion should have cleared us off the list.
*/
BUG_ON(!list_empty(&timer->it.cpu.entry));
} else {
spin_lock(&p->sighand->siglock);
if (timer->it.cpu.firing)
ret = TIMER_RETRY;
else
list_del(&timer->it.cpu.entry);
spin_unlock(&p->sighand->siglock);
}
read_unlock(&tasklist_lock);
WARN_ON_ONCE(p == NULL);
if (!ret)
put_task_struct(p);
/*
* Protect against sighand release/switch in exit/exec and process/
* thread timer list entry concurrent read/writes.
*/
sighand = lock_task_sighand(p, &flags);
if (unlikely(sighand == NULL)) {
/*
* We raced with the reaping of the task.
* The deletion should have cleared us off the list.
*/
WARN_ON_ONCE(!list_empty(&timer->it.cpu.entry));
} else {
if (timer->it.cpu.firing)
ret = TIMER_RETRY;
else
list_del(&timer->it.cpu.entry);
unlock_task_sighand(p, &flags);
}
if (!ret)
put_task_struct(p);
return ret;
}
static void cleanup_timers_list(struct list_head *head,
unsigned long long curr)
static void cleanup_timers_list(struct list_head *head)
{
struct cpu_timer_list *timer, *next;
......@@ -414,16 +425,11 @@ static void cleanup_timers_list(struct list_head *head,
* time for later timer_gettime calls to return.
* This must be called with the siglock held.
*/
static void cleanup_timers(struct list_head *head,
cputime_t utime, cputime_t stime,
unsigned long long sum_exec_runtime)
static void cleanup_timers(struct list_head *head)
{
cputime_t ptime = utime + stime;
cleanup_timers_list(head, cputime_to_expires(ptime));
cleanup_timers_list(++head, cputime_to_expires(utime));
cleanup_timers_list(++head, sum_exec_runtime);
cleanup_timers_list(head);
cleanup_timers_list(++head);
cleanup_timers_list(++head);
}
/*
......@@ -433,41 +439,14 @@ static void cleanup_timers(struct list_head *head,
*/
void posix_cpu_timers_exit(struct task_struct *tsk)
{
cputime_t utime, stime;
add_device_randomness((const void*) &tsk->se.sum_exec_runtime,
sizeof(unsigned long long));
task_cputime(tsk, &utime, &stime);
cleanup_timers(tsk->cpu_timers,
utime, stime, tsk->se.sum_exec_runtime);
cleanup_timers(tsk->cpu_timers);
}
void posix_cpu_timers_exit_group(struct task_struct *tsk)
{
struct signal_struct *const sig = tsk->signal;
cputime_t utime, stime;
task_cputime(tsk, &utime, &stime);
cleanup_timers(tsk->signal->cpu_timers,
utime + sig->utime, stime + sig->stime,
tsk->se.sum_exec_runtime + sig->sum_sched_runtime);
}
static void clear_dead_task(struct k_itimer *itimer, unsigned long long now)
{
struct cpu_timer_list *timer = &itimer->it.cpu;
/*
* That's all for this thread or process.
* We leave our residual in expires to be reported.
*/
put_task_struct(timer->task);
timer->task = NULL;
if (timer->expires < now) {
timer->expires = 0;
} else {
timer->expires -= now;
}
cleanup_timers(tsk->signal->cpu_timers);
}
static inline int expires_gt(cputime_t expires, cputime_t new_exp)
......@@ -477,8 +456,7 @@ static inline int expires_gt(cputime_t expires, cputime_t new_exp)
/*
* Insert the timer on the appropriate list before any timers that
* expire later. This must be called with the tasklist_lock held
* for reading, interrupts disabled and p->sighand->siglock taken.
* expire later. This must be called with the sighand lock held.
*/
static void arm_timer(struct k_itimer *timer)
{
......@@ -569,7 +547,8 @@ static void cpu_timer_fire(struct k_itimer *timer)
/*
* Sample a process (thread group) timer for the given group_leader task.
* Must be called with tasklist_lock held for reading.
* Must be called with task sighand lock held for safe while_each_thread()
* traversal.
*/
static int cpu_timer_sample_group(const clockid_t which_clock,
struct task_struct *p,
......@@ -632,43 +611,39 @@ static inline void posix_cpu_timer_kick_nohz(void) { }
* If we return TIMER_RETRY, it's necessary to release the timer's lock
* and try again. (This happens when the timer is in the middle of firing.)
*/
static int posix_cpu_timer_set(struct k_itimer *timer, int flags,
static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
struct itimerspec *new, struct itimerspec *old)
{
unsigned long flags;
struct sighand_struct *sighand;
struct task_struct *p = timer->it.cpu.task;
unsigned long long old_expires, new_expires, old_incr, val;
int ret;
if (unlikely(p == NULL)) {
/*
* Timer refers to a dead task's clock.
*/
return -ESRCH;
}
WARN_ON_ONCE(p == NULL);
new_expires = timespec_to_sample(timer->it_clock, &new->it_value);
read_lock(&tasklist_lock);
/*
* We need the tasklist_lock to protect against reaping that
* clears p->sighand. If p has just been reaped, we can no
* Protect against sighand release/switch in exit/exec and p->cpu_timers
* and p->signal->cpu_timers read/write in arm_timer()
*/
sighand = lock_task_sighand(p, &flags);
/*
* If p has just been reaped, we can no
* longer get any information about it at all.
*/
if (unlikely(p->sighand == NULL)) {
read_unlock(&tasklist_lock);
put_task_struct(p);
timer->it.cpu.task = NULL;
if (unlikely(sighand == NULL)) {
return -ESRCH;
}
/*
* Disarm any old timer after extracting its expiry time.
*/
BUG_ON(!irqs_disabled());
WARN_ON_ONCE(!irqs_disabled());
ret = 0;
old_incr = timer->it.cpu.incr;
spin_lock(&p->sighand->siglock);
old_expires = timer->it.cpu.expires;
if (unlikely(timer->it.cpu.firing)) {
timer->it.cpu.firing = -1;
......@@ -725,12 +700,11 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int flags,
* disable this firing since we are already reporting
* it as an overrun (thanks to bump_cpu_timer above).
*/
spin_unlock(&p->sighand->siglock);
read_unlock(&tasklist_lock);
unlock_task_sighand(p, &flags);
goto out;
}
if (new_expires != 0 && !(flags & TIMER_ABSTIME)) {
if (new_expires != 0 && !(timer_flags & TIMER_ABSTIME)) {
new_expires += val;
}
......@@ -744,9 +718,7 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int flags,
arm_timer(timer);
}
spin_unlock(&p->sighand->siglock);
read_unlock(&tasklist_lock);
unlock_task_sighand(p, &flags);
/*
* Install the new reload setting, and
* set up the signal and overrun bookkeeping.
......@@ -788,7 +760,8 @@ static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec *itp)
{
unsigned long long now;
struct task_struct *p = timer->it.cpu.task;
int clear_dead;
WARN_ON_ONCE(p == NULL);
/*
* Easy part: convert the reload time.
......@@ -801,52 +774,34 @@ static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec *itp)
return;
}
if (unlikely(p == NULL)) {
/*
* This task already died and the timer will never fire.
* In this case, expires is actually the dead value.
*/
dead:
sample_to_timespec(timer->it_clock, timer->it.cpu.expires,
&itp->it_value);
return;
}
/*
* Sample the clock to take the difference with the expiry time.
*/
if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
cpu_clock_sample(timer->it_clock, p, &now);
clear_dead = p->exit_state;
} else {
read_lock(&tasklist_lock);
if (unlikely(p->sighand == NULL)) {
struct sighand_struct *sighand;
unsigned long flags;
/*
* Protect against sighand release/switch in exit/exec and
* also make timer sampling safe if it ends up calling
* thread_group_cputime().
*/
sighand = lock_task_sighand(p, &flags);
if (unlikely(sighand == NULL)) {
/*
* The process has been reaped.
* We can't even collect a sample any more.
* Call the timer disarmed, nothing else to do.
*/
put_task_struct(p);
timer->it.cpu.task = NULL;
timer->it.cpu.expires = 0;
read_unlock(&tasklist_lock);
goto dead;
sample_to_timespec(timer->it_clock, timer->it.cpu.expires,
&itp->it_value);
} else {
cpu_timer_sample_group(timer->it_clock, p, &now);
clear_dead = (unlikely(p->exit_state) &&
thread_group_empty(p));
unlock_task_sighand(p, &flags);
}
read_unlock(&tasklist_lock);
}
if (unlikely(clear_dead)) {
/*
* We've noticed that the thread is dead, but
* not yet reaped. Take this opportunity to
* drop our task ref.
*/
clear_dead_task(timer, now);
goto dead;
}
if (now < timer->it.cpu.expires) {
......@@ -1060,14 +1015,12 @@ static void check_process_timers(struct task_struct *tsk,
*/
void posix_cpu_timer_schedule(struct k_itimer *timer)
{
struct sighand_struct *sighand;
unsigned long flags;
struct task_struct *p = timer->it.cpu.task;
unsigned long long now;
if (unlikely(p == NULL))
/*
* The task was cleaned up already, no future firings.
*/
goto out;
WARN_ON_ONCE(p == NULL);
/*
* Fetch the current sample and update the timer's expiry time.
......@@ -1075,52 +1028,45 @@ void posix_cpu_timer_schedule(struct k_itimer *timer)
if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
cpu_clock_sample(timer->it_clock, p, &now);
bump_cpu_timer(timer, now);
if (unlikely(p->exit_state)) {
clear_dead_task(timer, now);
if (unlikely(p->exit_state))
goto out;
/* Protect timer list r/w in arm_timer() */
sighand = lock_task_sighand(p, &flags);
if (!sighand)
goto out;
}
read_lock(&tasklist_lock); /* arm_timer needs it. */
spin_lock(&p->sighand->siglock);
} else {
read_lock(&tasklist_lock);
if (unlikely(p->sighand == NULL)) {
/*
* Protect arm_timer() and timer sampling in case of call to
* thread_group_cputime().
*/
sighand = lock_task_sighand(p, &flags);
if (unlikely(sighand == NULL)) {
/*
* The process has been reaped.
* We can't even collect a sample any more.
*/
put_task_struct(p);
timer->it.cpu.task = p = NULL;
timer->it.cpu.expires = 0;
read_unlock(&tasklist_lock);
goto out;
} else if (unlikely(p->exit_state) && thread_group_empty(p)) {
/*
* We've noticed that the thread is dead, but
* not yet reaped. Take this opportunity to
* drop our task ref.
*/
cpu_timer_sample_group(timer->it_clock, p, &now);
clear_dead_task(timer, now);
read_unlock(&tasklist_lock);
unlock_task_sighand(p, &flags);
/* Optimizations: if the process is dying, no need to rearm */
goto out;
}
spin_lock(&p->sighand->siglock);
cpu_timer_sample_group(timer->it_clock, p, &now);
bump_cpu_timer(timer, now);
/* Leave the tasklist_lock locked for the call below. */
/* Leave the sighand locked for the call below. */
}
/*
* Now re-arm for the new expiry time.
*/
BUG_ON(!irqs_disabled());
WARN_ON_ONCE(!irqs_disabled());
arm_timer(timer);
spin_unlock(&p->sighand->siglock);
read_unlock(&tasklist_lock);
unlock_task_sighand(p, &flags);
/* Kick full dynticks CPUs in case they need to tick on the new timer */
posix_cpu_timer_kick_nohz();
out:
timer->it_overrun_last = timer->it_overrun;
timer->it_overrun = -1;
......@@ -1204,7 +1150,7 @@ void run_posix_cpu_timers(struct task_struct *tsk)
struct k_itimer *timer, *next;
unsigned long flags;
BUG_ON(!irqs_disabled());
WARN_ON_ONCE(!irqs_disabled());
/*
* The fast path checks that there are no expired thread or thread
......@@ -1271,7 +1217,7 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
{
unsigned long long now;
BUG_ON(clock_idx == CPUCLOCK_SCHED);
WARN_ON_ONCE(clock_idx == CPUCLOCK_SCHED);
cpu_timer_sample_group(clock_idx, tsk, &now);
if (oldval) {
......
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