From: Paul E. McKenney Date: Fri, 3 Jan 2020 19:38:51 +0000 (-0800) Subject: rcu: Add WRITE_ONCE() to rcu_node ->qsmask update X-Git-Tag: v5.7-rc1~183^2^2^2~24 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=7672d647ddae37d2ea267159950bcc311e962434;p=thirdparty%2Flinux.git rcu: Add WRITE_ONCE() to rcu_node ->qsmask update The rcu_node structure's ->qsmask field is read locklessly, so this commit adds the WRITE_ONCE() to an update in order to provide proper documentation and READ_ONCE()/WRITE_ONCE() pairing. This data race was reported by KCSAN. Not appropriate for backporting due to failure being unlikely. Signed-off-by: Paul E. McKenney --- diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index d91c9156fab2e..bb57c24dbe9a5 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1881,7 +1881,7 @@ static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp, WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */ WARN_ON_ONCE(!rcu_is_leaf_node(rnp) && rcu_preempt_blocked_readers_cgp(rnp)); - rnp->qsmask &= ~mask; + WRITE_ONCE(rnp->qsmask, rnp->qsmask & ~mask); trace_rcu_quiescent_state_report(rcu_state.name, rnp->gp_seq, mask, rnp->qsmask, rnp->level, rnp->grplo, rnp->grphi,