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Subject[PATCH 2/5] posix-cpu-timers: Remove unnecessary locking around cpu_clock_sample_group

As of e78c3496790e ("time, signal: Protect resource use statistics
with seqlock") cpu_clock_sample_group no longers needs siglock
protection. Unfortunately no one realized it at the time.

Remove the extra locking that is for cpu_clock_sample_group and not
for cpu_clock_sample. This significantly simplifies the code.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
kernel/time/posix-cpu-timers.c | 55 +++++-----------------------------
1 file changed, 7 insertions(+), 48 deletions(-)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 46cc188bf5ab..3b27710f9505 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -721,27 +721,7 @@ static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp
if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
now = cpu_clock_sample(clkid, p);
} else {
- 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.
- * Disarm the timer, nothing else to do.
- */
- cpu_timer_setexpires(ctmr, 0);
- return;
- } else {
- now = cpu_clock_sample_group(clkid, p, false);
- unlock_task_sighand(p, &flags);
- }
+ now = cpu_clock_sample_group(clkid, p, false);
}

if (now < expires) {
@@ -988,41 +968,20 @@ static void posix_cpu_timer_rearm(struct k_itimer *timer)
*/
if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
now = cpu_clock_sample(clkid, p);
- bump_cpu_timer(timer, now);
- if (unlikely(p->exit_state))
- return;
-
- /* Protect timer list r/w in arm_timer() */
- sighand = lock_task_sighand(p, &flags);
- if (!sighand)
- return;
} else {
- /*
- * 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.
- */
- cpu_timer_setexpires(ctmr, 0);
- return;
- } else if (unlikely(p->exit_state) && thread_group_empty(p)) {
- /* If the process is dying, no need to rearm */
- goto unlock;
- }
now = cpu_clock_sample_group(clkid, p, true);
- bump_cpu_timer(timer, now);
- /* Leave the sighand locked for the call below. */
}
+ bump_cpu_timer(timer, now);
+
+ /* Protect timer list r/w in arm_timer() */
+ sighand = lock_task_sighand(p, &flags);
+ if (unlikely(sighand == NULL))
+ return;

/*
* Now re-arm for the new expiry time.
*/
arm_timer(timer);
-unlock:
unlock_task_sighand(p, &flags);
}

--
2.25.0
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