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Subject[tip: timers/core] posix-cpu-timers: Remove unnecessary locking around cpu_clock_sample_group
The following commit has been merged into the timers/core branch of tip:

Commit-ID: 60f2ceaa8111d9ec51af87bde4a6809f2b3235e4
Gitweb: https://git.kernel.org/tip/60f2ceaa8111d9ec51af87bde4a6809f2b3235e4
Author: Eric W. Biederman <ebiederm@xmission.com>
AuthorDate: Fri, 28 Feb 2020 11:09:19 -06:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Sun, 01 Mar 2020 11:21:44 +01:00

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>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/878skmvdts.fsf@x220.int.ebiederm.org

---
kernel/time/posix-cpu-timers.c | 66 ++++++---------------------------
1 file changed, 12 insertions(+), 54 deletions(-)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 46cc188..40c2d83 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -718,31 +718,10 @@ static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp
/*
* Sample the clock to take the difference with the expiry time.
*/
- if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
+ 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);
- }
- }
+ else
+ now = cpu_clock_sample_group(clkid, p, false);

if (now < expires) {
itp->it_value = ns_to_timespec64(expires - now);
@@ -986,43 +965,22 @@ static void posix_cpu_timer_rearm(struct k_itimer *timer)
/*
* Fetch the current sample and update the timer's expiry time.
*/
- if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
+ 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;
- }
+ else
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);
}

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