On Fri, Feb 14, 2020 at 04:29:29PM -0800, paulmck@xxxxxxxxxx wrote: > From: "Paul E. McKenney" <paulmck@xxxxxxxxxx> > > The srcu_node structure's ->srcu_gp_seq_needed_exp field is accessed > locklessly, so updates must use WRITE_ONCE(). This commit therefore > adds the needed WRITE_ONCE() invocations. > > This data race was reported by KCSAN. Not appropriate for backporting > due to failure being unlikely. This does indeed look like there can be a failure; but this Changelog fails to describe an actual problem. > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > --- > kernel/rcu/srcutree.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > index 657e6a7..b1edac9 100644 > --- a/kernel/rcu/srcutree.c > +++ b/kernel/rcu/srcutree.c > @@ -550,7 +550,7 @@ static void srcu_gp_end(struct srcu_struct *ssp) > snp->srcu_have_cbs[idx] = gpseq; > rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1); > if (ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, gpseq)) > - snp->srcu_gp_seq_needed_exp = gpseq; > + WRITE_ONCE(snp->srcu_gp_seq_needed_exp, gpseq); > mask = snp->srcu_data_have_cbs[idx]; > snp->srcu_data_have_cbs[idx] = 0; > spin_unlock_irq_rcu_node(snp); > @@ -660,7 +660,7 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp, > if (snp == sdp->mynode) > snp->srcu_data_have_cbs[idx] |= sdp->grpmask; > if (!do_norm && ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, s)) > - snp->srcu_gp_seq_needed_exp = s; > + WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s); > spin_unlock_irqrestore_rcu_node(snp, flags); > } > > -- > 2.9.5 >
