Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH tip/core/rcu 37/40] rcu: Regularize resetting of rcu_data wrap indicator | Date | Mon, 25 Jun 2018 17:08:56 -0700 |
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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@linux.vnet.ibm.com> --- 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 fa82f0413d2c..ad76aeade637 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; } -- 2.17.1
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