posix-timers: Remove remaining uses of tasklist_lock
The remaining uses of tasklist_lock were mostly about synchronizing
against sighand modifications, getting coherent and safe group samples
and also thread/process wide timers list handling.
All of this is already safely synchronizable with the target's
sighand lock. Let's use it on these places instead.
Also update the comments about locking.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 9641958..d9dc5ed 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -233,7 +233,8 @@
/*
* 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,
@@ -455,8 +456,7 @@
/*
* 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)
{
@@ -547,7 +547,8 @@
/*
* 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,
@@ -610,9 +611,11 @@
* 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;
@@ -621,14 +624,16 @@
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);
+ if (unlikely(sighand == NULL)) {
return -ESRCH;
}
@@ -639,7 +644,6 @@
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;
@@ -696,12 +700,11 @@
* 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;
}
@@ -715,9 +718,7 @@
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.
@@ -779,8 +780,16 @@
if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
cpu_clock_sample(timer->it_clock, p, &now);
} 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.
@@ -789,11 +798,10 @@
timer->it.cpu.expires = 0;
sample_to_timespec(timer->it_clock, timer->it.cpu.expires,
&itp->it_value);
- read_unlock(&tasklist_lock);
} else {
cpu_timer_sample_group(timer->it_clock, p, &now);
+ unlock_task_sighand(p, &flags);
}
- read_unlock(&tasklist_lock);
}
if (now < timer->it.cpu.expires) {
@@ -1007,6 +1015,8 @@
*/
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;
@@ -1021,27 +1031,31 @@
if (unlikely(p->exit_state))
goto out;
- read_lock(&tasklist_lock); /* arm_timer needs it. */
- spin_lock(&p->sighand->siglock);
+ /* Protect timer list r/w in arm_timer() */
+ sighand = lock_task_sighand(p, &flags);
+ if (!sighand)
+ goto out;
} 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.
*/
timer->it.cpu.expires = 0;
- read_unlock(&tasklist_lock);
goto out;
} else if (unlikely(p->exit_state) && thread_group_empty(p)) {
- 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. */
}
/*
@@ -1049,12 +1063,10 @@
*/
BUG_ON(!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;
