4.14-stable review patch. If anyone has any objections, please let me know.
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From: Anna-Maria Gleixner anna-maria@linutronix.de
commit ced6d5c11d3e7b342f1a80f908e6756ebd4b8ddd upstream.
During boot and before base::nohz_active is set in the timer bases, deferrable timers are enqueued into the standard timer base. This works correctly as long as base::nohz_active is false.
Once it base::nohz_active is set and a timer which was enqueued before that is accessed the lock selector code choses the lock of the deferred base. This causes unlocked access to the standard base and in case the timer is removed it does not clear the pending flag in the standard base bitmap which causes get_next_timer_interrupt() to return bogus values.
To prevent that, the deferrable timers must be enqueued in the deferrable base, even when base::nohz_active is not set. Those deferrable timers also need to be expired unconditional.
Fixes: 500462a9de65 ("timers: Switch to a non-cascading wheel") Signed-off-by: Anna-Maria Gleixner anna-maria@linutronix.de Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Frederic Weisbecker fweisbec@gmail.com Cc: Peter Zijlstra peterz@infradead.org Cc: Sebastian Siewior bigeasy@linutronix.de Cc: rt@linutronix.de Cc: Paul McKenney paulmck@linux.vnet.ibm.com Link: https://lkml.kernel.org/r/20171222145337.633328378@linutronix.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/time/timer.c | 16 +++++++--------- 1 file changed, 7 insertions(+), 9 deletions(-)
--- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -814,11 +814,10 @@ static inline struct timer_base *get_tim struct timer_base *base = per_cpu_ptr(&timer_bases[BASE_STD], cpu);
/* - * If the timer is deferrable and nohz is active then we need to use - * the deferrable base. + * If the timer is deferrable and NO_HZ_COMMON is set then we need + * to use the deferrable base. */ - if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && base->nohz_active && - (tflags & TIMER_DEFERRABLE)) + if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && (tflags & TIMER_DEFERRABLE)) base = per_cpu_ptr(&timer_bases[BASE_DEF], cpu); return base; } @@ -828,11 +827,10 @@ static inline struct timer_base *get_tim struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
/* - * If the timer is deferrable and nohz is active then we need to use - * the deferrable base. + * If the timer is deferrable and NO_HZ_COMMON is set then we need + * to use the deferrable base. */ - if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && base->nohz_active && - (tflags & TIMER_DEFERRABLE)) + if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && (tflags & TIMER_DEFERRABLE)) base = this_cpu_ptr(&timer_bases[BASE_DEF]); return base; } @@ -1644,7 +1642,7 @@ static __latent_entropy void run_timer_s base->must_forward_clk = false;
__run_timers(base); - if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && base->nohz_active) + if (IS_ENABLED(CONFIG_NO_HZ_COMMON)) __run_timers(this_cpu_ptr(&timer_bases[BASE_DEF])); }