[PATCH 06/16] rcu: Clear gp_flags only when actually starting new gp

[Pranith Kumar <bobby.prani@gmail.com>]

We are clearing the gp_flags before we check if a grace period is in progress.
If a grace period is in progress, we return after incorrectly clearing the
gp_flags. The code comments say that this is highly unlikely, but just to be
safe this commit moves the clearing of gp_flags to after the check for grace
period in progress.

Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
---
 kernel/rcu/tree.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 044946e..b14cecd 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1605,7 +1605,6 @@ static int rcu_gp_init(struct rcu_state *rsp)
 		raw_spin_unlock_irq(&rnp->lock);
 		return 0;
 	}
-	ACCESS_ONCE(rsp->gp_flags) = 0; /* Clear all flags: New grace period. */
 
 	if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
 		/*
@@ -1616,6 +1615,8 @@ static int rcu_gp_init(struct rcu_state *rsp)
 		return 0;
 	}
 
+	ACCESS_ONCE(rsp->gp_flags) = 0; /* Clear all flags: New grace period. */
+
 	/* Advance to a new grace period and initialize state. */
 	record_gp_stall_check_time(rsp);
 	/* Record GP times before starting GP, hence smp_store_release(). */
-- 
2.0.0.rc2