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Date: Tue, 24 Mar 2020 09:16:51 -0000 From: "tip-bot2 for Paul E. McKenney" <tip-bot2@...utronix.de> To: linux-tip-commits@...r.kernel.org Cc: "Paul E. McKenney" <paulmck@...nel.org>, x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org> Subject: [tip: core/rcu] rcu: Add READ_ONCE() to rcu_data ->gpwrap The following commit has been merged into the core/rcu branch of tip: Commit-ID: a5b8950180f8e5acb802d1672e0b4d0ceee6126e Gitweb: https://git.kernel.org/tip/a5b8950180f8e5acb802d1672e0b4d0ceee6126e Author: Paul E. McKenney <paulmck@...nel.org> AuthorDate: Tue, 07 Jan 2020 15:48:39 -08:00 Committer: Paul E. McKenney <paulmck@...nel.org> CommitterDate: Thu, 20 Feb 2020 15:58:22 -08:00 rcu: Add READ_ONCE() to rcu_data ->gpwrap The rcu_data structure's ->gpwrap field is read locklessly, and so this commit adds the required READ_ONCE() to a pair of laods in order to avoid destructive compiler optimizations. This data race was reported by KCSAN. Signed-off-by: Paul E. McKenney <paulmck@...nel.org> --- kernel/rcu/tree.c | 2 +- kernel/rcu/tree_stall.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index a70f56b..e851a12 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1322,7 +1322,7 @@ static void rcu_accelerate_cbs_unlocked(struct rcu_node *rnp, rcu_lockdep_assert_cblist_protected(rdp); c = rcu_seq_snap(&rcu_state.gp_seq); - if (!rdp->gpwrap && ULONG_CMP_GE(rdp->gp_seq_needed, c)) { + if (!READ_ONCE(rdp->gpwrap) && ULONG_CMP_GE(rdp->gp_seq_needed, c)) { /* Old request still live, so mark recent callbacks. */ (void)rcu_segcblist_accelerate(&rdp->cblist, c); return; diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 43dc688..bca637b 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -602,7 +602,7 @@ void show_rcu_gp_kthreads(void) continue; for_each_leaf_node_possible_cpu(rnp, cpu) { rdp = per_cpu_ptr(&rcu_data, cpu); - if (rdp->gpwrap || + if (READ_ONCE(rdp->gpwrap) || ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq), READ_ONCE(rdp->gp_seq_needed))) continue;
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