From a542d116bab28b4bcade2f41488f4617373c620f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 7 Mar 2024 20:11:21 -0800 Subject: rcu: Mark writes to rcu_sync ->gp_count field The rcu_sync structure's ->gp_count field is updated under the protection of ->rss_lock, but read locklessly, and KCSAN noted the data race. This commit therefore uses WRITE_ONCE() to do this update to clearly document its racy nature. Signed-off-by: Paul E. McKenney Cc: Oleg Nesterov Cc: Peter Zijlstra Signed-off-by: Uladzislau Rezki (Sony) --- kernel/rcu/sync.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c index 86df878a2fee..6c2bd9001adc 100644 --- a/kernel/rcu/sync.c +++ b/kernel/rcu/sync.c @@ -122,7 +122,7 @@ void rcu_sync_enter(struct rcu_sync *rsp) * we are called at early boot time but this shouldn't happen. */ } - rsp->gp_count++; + WRITE_ONCE(rsp->gp_count, rsp->gp_count + 1); spin_unlock_irq(&rsp->rss_lock); if (gp_state == GP_IDLE) { @@ -151,11 +151,15 @@ void rcu_sync_enter(struct rcu_sync *rsp) */ void rcu_sync_exit(struct rcu_sync *rsp) { + int gpc; + WARN_ON_ONCE(READ_ONCE(rsp->gp_state) == GP_IDLE); WARN_ON_ONCE(READ_ONCE(rsp->gp_count) == 0); spin_lock_irq(&rsp->rss_lock); - if (!--rsp->gp_count) { + gpc = rsp->gp_count - 1; + WRITE_ONCE(rsp->gp_count, gpc); + if (!gpc) { if (rsp->gp_state == GP_PASSED) { WRITE_ONCE(rsp->gp_state, GP_EXIT); rcu_sync_call(rsp); -- cgit v1.2.3