Commit-ID: 3d18469a2bb3988e669d67e097eff42dd40663d4 Gitweb: https://git.kernel.org/tip/3d18469a2bb3988e669d67e097eff42dd40663d4 Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> AuthorDate: Tue, 15 May 2018 16:47:30 -0700 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Thu, 12 Jul 2018 15:38:56 -0700 rcu: Regularize resetting of rcu_data wrap indicator The rcu_data structure's ->gpwrap indicator is currently reset only when the CPU in question detects a new grace period. This is in theory sufficient because any CPU that has been out of action for long enough that its ->gpwrap indicator is set is guaranteed to see both the end of an old grace period and the start of a new one. However, the current code leaves a short window during which the ->gpwrap indicator has been reset but the corresponding ->gp_seq counter has not yet been brought up to date. This is harmless because interrupts are disabled, but it is likely to (at the very least) cause confusion. This commit therefore moves the resetting of ->gpwrap to follow the updating of ->gp_seq. While in the area, it also resets ->gp_seq_needed. Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> --- kernel/rcu/tree.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index fa219eea0ae7..161e8fb8b83f 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1807,10 +1807,12 @@ static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp, rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr); rdp->core_needs_qs = need_gp; zero_cpu_stall_ticks(rdp); - WRITE_ONCE(rdp->gpwrap, false); - rcu_gpnum_ovf(rnp, rdp); } rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */ + if (ULONG_CMP_GE(rnp->gp_seq_needed, rdp->gp_seq_needed) || rdp->gpwrap) + rdp->gp_seq_needed = rnp->gp_seq_needed; + WRITE_ONCE(rdp->gpwrap, false); + rcu_gpnum_ovf(rnp, rdp); return ret; } -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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