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A samll set of timer related fixes:

Browse source 
- Plug a race between rearm and process tick in the posix CPU timers code
 
  - Make the optimization to avoid recalculation of the next timer interrupt
    work correctly when there are no timers pending.
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Merge tag 'timers-urgent-2021-07-25' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timer fixes from Thomas Gleixner:
 "A small set of timer related fixes:

   - Plug a race between rearm and process tick in the posix CPU timers
     code

   - Make the optimization to avoid recalculation of the next timer
     interrupt work correctly when there are no timers pending"

* tag 'timers-urgent-2021-07-25' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  timers: Fix get_next_timer_interrupt() with no timers pending
  posix-cpu-timers: Fix rearm racing against process tick
This commit is contained in:
Linus Torvalds 2021-07-25 10:27:44 -07:00
commit 12e9bd168c
2 changed files with 10 additions and 8 deletions
Download patch file Download diff file Expand all files Collapse all files

10
kernel/time/posix-cpu-timers.c
View file

@ -991,6 +991,11 @@ static void posix_cpu_timer_rearm(struct k_itimer *timer)
if (!p)
goto out;
/* Protect timer list r/w in arm_timer() */
sighand = lock_task_sighand(p, &flags);
if (unlikely(sighand == NULL))
goto out;
/*
* Fetch the current sample and update the timer's expiry time.
*/
@ -1001,11 +1006,6 @@ static void posix_cpu_timer_rearm(struct k_itimer *timer)
bump_cpu_timer(timer, now);
/* Protect timer list r/w in arm_timer() */
sighand = lock_task_sighand(p, &flags);
if (unlikely(sighand == NULL))
goto out;
/*
* Now re-arm for the new expiry time.
*/

8
kernel/time/timer.c
View file

@ -207,6 +207,7 @@ struct timer_base {
unsigned int cpu;
bool next_expiry_recalc;
bool is_idle;
bool timers_pending;
DECLARE_BITMAP(pending_map, WHEEL_SIZE);
struct hlist_head vectors[WHEEL_SIZE];
} ____cacheline_aligned;
@ -595,6 +596,7 @@ static void enqueue_timer(struct timer_base *base, struct timer_list *timer,
* can reevaluate the wheel:
*/
base->next_expiry = bucket_expiry;
base->timers_pending = true;
base->next_expiry_recalc = false;
trigger_dyntick_cpu(base, timer);
}
@ -1582,6 +1584,7 @@ static unsigned long __next_timer_interrupt(struct timer_base *base)
}
base->next_expiry_recalc = false;
base->timers_pending = !(next == base->clk + NEXT_TIMER_MAX_DELTA);
return next;
}
@ -1633,7 +1636,6 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
u64 expires = KTIME_MAX;
unsigned long nextevt;
bool is_max_delta;
/*
* Pretend that there is no timer pending if the cpu is offline.
@ -1646,7 +1648,6 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
if (base->next_expiry_recalc)
base->next_expiry = __next_timer_interrupt(base);
nextevt = base->next_expiry;
is_max_delta = (nextevt == base->clk + NEXT_TIMER_MAX_DELTA);
/*
* We have a fresh next event. Check whether we can forward the
@ -1664,7 +1665,7 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
expires = basem;
base->is_idle = false;
} else {
if (!is_max_delta)
if (base->timers_pending)
expires = basem + (u64)(nextevt - basej) * TICK_NSEC;
/*
* If we expect to sleep more than a tick, mark the base idle.
@ -1947,6 +1948,7 @@ int timers_prepare_cpu(unsigned int cpu)
base = per_cpu_ptr(&timer_bases[b], cpu);
base->clk = jiffies;
base->next_expiry = base->clk + NEXT_TIMER_MAX_DELTA;
base->timers_pending = false;
base->is_idle = false;
}
return 0;