srcu: Avoid NULL dereference in srcu_torture_stats_print()

You really shouldn't invoke srcu_torture_stats_print() after invoking
cleanup_srcu_struct(), but there is really no reason to get a
compiler-obfuscated per-CPU-variable NULL pointer dereference as the
diagnostic.  This commit therefore checks for NULL ->sda and makes a
more polite console-message complaint in that case.

Co-developed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 9dd048989027c7f99c1ca941fa2188bd00b4cf67..b7138dbe1a2d2afa74fe295bd04ac10d58164b92 100644 (file)
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -1477,37 +1477,43 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
        idx = ssp->srcu_idx & 0x1;
        if (ss_state < 0 || ss_state >= ARRAY_SIZE(srcu_size_state_name))
                ss_state_idx = ARRAY_SIZE(srcu_size_state_name) - 1;
-       pr_alert("%s%s Tree SRCU g%ld state %d (%s) per-CPU(idx=%d):",
+       pr_alert("%s%s Tree SRCU g%ld state %d (%s)",
                 tt, tf, rcu_seq_current(&ssp->srcu_gp_seq), ss_state,
-                srcu_size_state_name[ss_state_idx], idx);
-       for_each_possible_cpu(cpu) {
-               unsigned long l0, l1;
-               unsigned long u0, u1;
-               long c0, c1;
-               struct srcu_data *sdp;
-
-               sdp = per_cpu_ptr(ssp->sda, cpu);
-               u0 = data_race(sdp->srcu_unlock_count[!idx]);
-               u1 = data_race(sdp->srcu_unlock_count[idx]);
+                srcu_size_state_name[ss_state_idx]);
+       if (!ssp->sda) {
+               // Called after cleanup_srcu_struct(), perhaps.
+               pr_cont(" No per-CPU srcu_data structures (->sda == NULL).\n");
+       } else {
+               pr_cont(" per-CPU(idx=%d):", idx);
+               for_each_possible_cpu(cpu) {
+                       unsigned long l0, l1;
+                       unsigned long u0, u1;
+                       long c0, c1;
+                       struct srcu_data *sdp;
 
-               /*
-                * Make sure that a lock is always counted if the corresponding
-                * unlock is counted.
-                */
-               smp_rmb();
-
-               l0 = data_race(sdp->srcu_lock_count[!idx]);
-               l1 = data_race(sdp->srcu_lock_count[idx]);
-
-               c0 = l0 - u0;
-               c1 = l1 - u1;
-               pr_cont(" %d(%ld,%ld %c)",
-                       cpu, c0, c1,
-                       "C."[rcu_segcblist_empty(&sdp->srcu_cblist)]);
-               s0 += c0;
-               s1 += c1;
+                       sdp = per_cpu_ptr(ssp->sda, cpu);
+                       u0 = data_race(sdp->srcu_unlock_count[!idx]);
+                       u1 = data_race(sdp->srcu_unlock_count[idx]);
+
+                       /*
+                        * Make sure that a lock is always counted if the corresponding
+                        * unlock is counted.
+                        */
+                       smp_rmb();
+
+                       l0 = data_race(sdp->srcu_lock_count[!idx]);
+                       l1 = data_race(sdp->srcu_lock_count[idx]);
+
+                       c0 = l0 - u0;
+                       c1 = l1 - u1;
+                       pr_cont(" %d(%ld,%ld %c)",
+                               cpu, c0, c1,
+                               "C."[rcu_segcblist_empty(&sdp->srcu_cblist)]);
+                       s0 += c0;
+                       s1 += c1;
+               }
+               pr_cont(" T(%ld,%ld)\n", s0, s1);
        }
-       pr_cont(" T(%ld,%ld)\n", s0, s1);
        if (READ_ONCE(ssp->srcu_size_state) == SRCU_SIZE_SMALL && convert_to_big == 2)
                WRITE_ONCE(ssp->srcu_size_state, SRCU_SIZE_ALLOC);
 }