| Message ID | 20180618144741.339763-1-arnd@arndb.de |
|---|---|
| State | Superseded |
| Headers | show |
| Series | rcutorture: use monotonic timestamp for stall detection | expand |
On Mon, Jun 18, 2018 at 04:47:34PM +0200, Arnd Bergmann wrote: > The get_seconds() call is deprecated because it overflows on 32-bit > architectures. The algorithm in rcu_torture_stall() can deal with > the overflow, but another problem here is that using a CLOCK_REALTIME > stamp can lead to a false-positive stall warning when a settimeofday() > happens concurrently. > > Using ktime_get_seconds() instead avoids those issues and will never > overflow. The added cast to 'unsigned long' however is necessary to > make ULONG_CMP_LT() work correctly. > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> Queued for testing and review, thank you! If things go well, I expect this to be ready for the v4.19 merge window. Thanx, Paul > --- > kernel/rcu/rcutorture.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c > index 42fcb7f05fac..f42cf69ef539 100644 > --- a/kernel/rcu/rcutorture.c > +++ b/kernel/rcu/rcutorture.c > @@ -1446,7 +1446,7 @@ static int rcu_torture_stall(void *args) > VERBOSE_TOROUT_STRING("rcu_torture_stall end holdoff"); > } > if (!kthread_should_stop()) { > - stop_at = get_seconds() + stall_cpu; > + stop_at = ktime_get_seconds() + stall_cpu; > /* RCU CPU stall is expected behavior in following code. */ > rcu_read_lock(); > if (stall_cpu_irqsoff) > @@ -1455,7 +1455,8 @@ static int rcu_torture_stall(void *args) > preempt_disable(); > pr_alert("rcu_torture_stall start on CPU %d.\n", > smp_processor_id()); > - while (ULONG_CMP_LT(get_seconds(), stop_at)) > + while (ULONG_CMP_LT((unsigned long)ktime_get_seconds(), > + stop_at)) > continue; /* Induce RCU CPU stall warning. */ > if (stall_cpu_irqsoff) > local_irq_enable(); > -- > 2.9.0 >
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index 42fcb7f05fac..f42cf69ef539 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -1446,7 +1446,7 @@ static int rcu_torture_stall(void *args) VERBOSE_TOROUT_STRING("rcu_torture_stall end holdoff"); } if (!kthread_should_stop()) { - stop_at = get_seconds() + stall_cpu; + stop_at = ktime_get_seconds() + stall_cpu; /* RCU CPU stall is expected behavior in following code. */ rcu_read_lock(); if (stall_cpu_irqsoff) @@ -1455,7 +1455,8 @@ static int rcu_torture_stall(void *args) preempt_disable(); pr_alert("rcu_torture_stall start on CPU %d.\n", smp_processor_id()); - while (ULONG_CMP_LT(get_seconds(), stop_at)) + while (ULONG_CMP_LT((unsigned long)ktime_get_seconds(), + stop_at)) continue; /* Induce RCU CPU stall warning. */ if (stall_cpu_irqsoff) local_irq_enable();
The get_seconds() call is deprecated because it overflows on 32-bit architectures. The algorithm in rcu_torture_stall() can deal with the overflow, but another problem here is that using a CLOCK_REALTIME stamp can lead to a false-positive stall warning when a settimeofday() happens concurrently. Using ktime_get_seconds() instead avoids those issues and will never overflow. The added cast to 'unsigned long' however is necessary to make ULONG_CMP_LT() work correctly. Signed-off-by: Arnd Bergmann <arnd@arndb.de> --- kernel/rcu/rcutorture.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) -- 2.9.0