On Fri, Dec 02, 2022 at 02:18:37PM +0100, Uladzislau Rezki (Sony) wrote:
> A need_offload_krc() function is now lock-free. A compiler
> can optimize readers in way that they see an old value even
> though writers already updated the krcp->head from another
> path.
>
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Queued, thank you!!!
With the usual wordsmithing, so please let me know if I messed something
up.
Thanx, Paul
------------------------------------------------------------------------
commit 9615ca28bc2c94cf2e092f06baace941fbf3b7e8
Author: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Date: Fri Dec 2 14:18:37 2022 +0100
rcu/kvfree: Use READ_ONCE() when access to krcp->head
The need_offload_krc() function is now lock-free, which gives the
compiler freedom to load old values from plain C-language loads from
the kfree_rcu_cpu struture's ->head pointer. This commit therefore
applied READ_ONCE() to these loads.
Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 2d16a0eee792d..ee8a6a711719a 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3029,7 +3029,7 @@ need_offload_krc(struct kfree_rcu_cpu *krcp)
if (!list_empty(&krcp->bulk_head[i]))
return true;
- return !!krcp->head;
+ return !!READ_ONCE(krcp->head);
}
static void
@@ -3070,7 +3070,7 @@ static void kfree_rcu_monitor(struct work_struct *work)
// in that case the monitor work is rearmed.
if ((!list_empty(&krcp->bulk_head[0]) && list_empty(&krwp->bulk_head_free[0])) ||
(!list_empty(&krcp->bulk_head[1]) && list_empty(&krwp->bulk_head_free[1])) ||
- (krcp->head && !krwp->head_free)) {
+ (READ_ONCE(krcp->head) && !krwp->head_free)) {
// Channel 1 corresponds to the SLAB-pointer bulk path.
// Channel 2 corresponds to vmalloc-pointer bulk path.
