diff options
Diffstat (limited to 'kernel/rcu/rcu.h')
| -rw-r--r-- | kernel/rcu/rcu.h | 15 |
1 files changed, 14 insertions, 1 deletions
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index 89f13fffac73..d5e0294b8580 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -158,7 +158,20 @@ static inline bool rcu_seq_new_gp(unsigned long old, unsigned long new) */ static inline unsigned long rcu_seq_diff(unsigned long new, unsigned long old) { - return (new - old) >> RCU_SEQ_CTR_SHIFT; + unsigned long rnd_diff; + + if (old == new) + return 0; + /* + * Compute the number of grace periods (still shifted up), plus + * one if either of new and old is not an exact grace period. + */ + rnd_diff = (new & ~RCU_SEQ_STATE_MASK) - + ((old + RCU_SEQ_STATE_MASK) & ~RCU_SEQ_STATE_MASK) + + ((new & RCU_SEQ_STATE_MASK) || (old & RCU_SEQ_STATE_MASK)); + if (ULONG_CMP_GE(RCU_SEQ_STATE_MASK, rnd_diff)) + return 1; /* Definitely no grace period has elapsed. */ + return ((rnd_diff - RCU_SEQ_STATE_MASK - 1) >> RCU_SEQ_CTR_SHIFT) + 2; } /* |