From 8fe8ff09ce3b5750e1f3e45a1f4a81d59c7ff1f1 Mon Sep 17 00:00:00 2001 From: Kevin Hilman Date: Wed, 15 Jan 2014 14:51:38 +0100 Subject: [PATCH] sched/nohz: Fix overflow error in scheduler_tick_max_deferment() While calculating the scheduler tick max deferment, the delta is converted from microseconds to nanoseconds through a multiplication against NSEC_PER_USEC. But this microseconds operand is an unsigned int, thus the result may likely overflow. The result is cast to u64 but only once the operation is completed, which is too late to avoid overflown result. This is currently not a problem because the scheduler tick max deferment is 1 second. But this may become an issue as we plan to make this value tunable. So lets fix this by casting the usecs value to u64 before multiplying by NSECS_PER_USEC. Also to prevent from this kind of mistake to happen again, move this ad-hoc jiffies -> nsecs conversion to a new helper. Signed-off-by: Kevin Hilman Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Alex Shi Cc: Steven Rostedt Cc: Paul E. McKenney Cc: John Stultz Cc: Kevin Hilman Link: http://lkml.kernel.org/r/1387315388-31676-2-git-send-email-khilman@linaro.org [move ad-hoc conversion to jiffies_to_nsecs helper] Signed-off-by: Frederic Weisbecker --- include/linux/jiffies.h | 6 ++++++ kernel/sched/core.c | 2 +- 2 files changed, 7 insertions(+), 1 deletion(-) diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h index d235e88cfd7c..1f44466c1e9d 100644 --- a/include/linux/jiffies.h +++ b/include/linux/jiffies.h @@ -294,6 +294,12 @@ extern unsigned long preset_lpj; */ extern unsigned int jiffies_to_msecs(const unsigned long j); extern unsigned int jiffies_to_usecs(const unsigned long j); + +static inline u64 jiffies_to_nsecs(const unsigned long j) +{ + return (u64)jiffies_to_usecs(j) * NSEC_PER_USEC; +} + extern unsigned long msecs_to_jiffies(const unsigned int m); extern unsigned long usecs_to_jiffies(const unsigned int u); extern unsigned long timespec_to_jiffies(const struct timespec *value); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index a88f4a485c5e..61e601fc2b1e 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2325,7 +2325,7 @@ u64 scheduler_tick_max_deferment(void) if (time_before_eq(next, now)) return 0; - return jiffies_to_usecs(next - now) * NSEC_PER_USEC; + return jiffies_to_nsecs(next - now); } #endif -- 2.25.1