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| author | Paul E. McKenney <paulmck@kernel.org> | 2020-01-04 11:33:17 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2020-02-20 15:58:22 -0800 |
| commit | 8ff37290d6622e130553a38ec2662a728e46cdba (patch) | |
| tree | 5e44a2a33b07485e0657433245613c0c1692fbce /kernel/rcu/tree_stall.h | |
| parent | bfeebe24212d374f82bbf5b005371fe13acabb93 (diff) | |
| download | lwn-8ff37290d6622e130553a38ec2662a728e46cdba.tar.gz lwn-8ff37290d6622e130553a38ec2662a728e46cdba.zip | |
rcu: Add *_ONCE() for grace-period progress indicators
The various RCU structures' ->gp_seq, ->gp_seq_needed, ->gp_req_activity,
and ->gp_activity fields are read locklessly, so they must be updated with
WRITE_ONCE() and, when read locklessly, with READ_ONCE(). This commit makes
these changes.
This data race was reported by KCSAN. Not appropriate for backporting
due to failure being unlikely.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu/tree_stall.h')
| -rw-r--r-- | kernel/rcu/tree_stall.h | 26 |
1 files changed, 15 insertions, 11 deletions
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 55f9b84790d3..43dc688c3785 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -592,21 +592,22 @@ void show_rcu_gp_kthreads(void) (long)READ_ONCE(rcu_get_root()->gp_seq_needed), READ_ONCE(rcu_state.gp_flags)); rcu_for_each_node_breadth_first(rnp) { - if (ULONG_CMP_GE(rcu_state.gp_seq, rnp->gp_seq_needed)) + if (ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq), + READ_ONCE(rnp->gp_seq_needed))) continue; pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n", - rnp->grplo, rnp->grphi, (long)rnp->gp_seq, - (long)rnp->gp_seq_needed); + rnp->grplo, rnp->grphi, (long)READ_ONCE(rnp->gp_seq), + (long)READ_ONCE(rnp->gp_seq_needed)); if (!rcu_is_leaf_node(rnp)) continue; for_each_leaf_node_possible_cpu(rnp, cpu) { rdp = per_cpu_ptr(&rcu_data, cpu); if (rdp->gpwrap || - ULONG_CMP_GE(rcu_state.gp_seq, - rdp->gp_seq_needed)) + ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq), + READ_ONCE(rdp->gp_seq_needed))) continue; pr_info("\tcpu %d ->gp_seq_needed %ld\n", - cpu, (long)rdp->gp_seq_needed); + cpu, (long)READ_ONCE(rdp->gp_seq_needed)); } } for_each_possible_cpu(cpu) { @@ -631,7 +632,8 @@ static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, static atomic_t warned = ATOMIC_INIT(0); if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() || - ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed)) + ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq), + READ_ONCE(rnp_root->gp_seq_needed))) return; j = jiffies; /* Expensive access, and in common case don't get here. */ if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) || @@ -642,7 +644,8 @@ static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, raw_spin_lock_irqsave_rcu_node(rnp, flags); j = jiffies; if (rcu_gp_in_progress() || - ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) || + ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq), + READ_ONCE(rnp_root->gp_seq_needed)) || time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) || time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) || atomic_read(&warned)) { @@ -655,9 +658,10 @@ static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */ j = jiffies; if (rcu_gp_in_progress() || - ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) || - time_before(j, rcu_state.gp_req_activity + gpssdelay) || - time_before(j, rcu_state.gp_activity + gpssdelay) || + ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq), + READ_ONCE(rnp_root->gp_seq_needed)) || + time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) || + time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) || atomic_xchg(&warned, 1)) { if (rnp_root != rnp) /* irqs remain disabled. */ |