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authorThomas Gleixner <tglx@linutronix.de>2020-03-21 12:25:58 +0100
committerPeter Zijlstra <peterz@infradead.org>2020-03-21 16:00:23 +0100
commite5d4d1756b07d9490a0269a9e68c1e05ee1feb9b (patch)
tree27a6cf91053169846adab85b04a84cb9e763d2fb /kernel/time/jiffies.c
parent919e9e6395cfac23b7e71ed88930367459055daf (diff)
timekeeping: Split jiffies seqlock
seqlock consists of a sequence counter and a spinlock_t which is used to serialize the writers. spinlock_t is substituted by a "sleeping" spinlock on PREEMPT_RT enabled kernels which breaks the usage in the timekeeping code as the writers are executed in hard interrupt and therefore non-preemptible context even on PREEMPT_RT. The spinlock in seqlock cannot be unconditionally replaced by a raw_spinlock_t as many seqlock users have nesting spinlock sections or other code which is not suitable to run in truly atomic context on RT. Instead of providing a raw_seqlock API for a single use case, open code the seqlock for the jiffies use case and implement it with a raw_spinlock_t and a sequence counter. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20200321113242.120587764@linutronix.de
Diffstat (limited to 'kernel/time/jiffies.c')
-rw-r--r--kernel/time/jiffies.c7
1 files changed, 4 insertions, 3 deletions
diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
index d23b434c2ca7..eddcf4970444 100644
--- a/kernel/time/jiffies.c
+++ b/kernel/time/jiffies.c
@@ -58,7 +58,8 @@ static struct clocksource clocksource_jiffies = {
.max_cycles = 10,
};
-__cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock);
+__cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(jiffies_lock);
+__cacheline_aligned_in_smp seqcount_t jiffies_seq;
#if (BITS_PER_LONG < 64)
u64 get_jiffies_64(void)
@@ -67,9 +68,9 @@ u64 get_jiffies_64(void)
u64 ret;
do {
- seq = read_seqbegin(&jiffies_lock);
+ seq = read_seqcount_begin(&jiffies_seq);
ret = jiffies_64;
- } while (read_seqretry(&jiffies_lock, seq));
+ } while (read_seqcount_retry(&jiffies_seq, seq));
return ret;
}
EXPORT_SYMBOL(get_jiffies_64);