From: "Paul E. McKenney" <paulmck@kernel.org>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
rostedt@goodmis.org, "Paul E. McKenney" <paulmck@kernel.org>,
Neeraj Upadhyay <quic_neeraju@quicinc.com>
Subject: [PATCH rcu 13/21] srcu: Avoid NULL dereference in srcu_torture_stats_print()
Date: Mon, 18 Apr 2022 17:03:14 -0700 [thread overview]
Message-ID: <20220419000322.3948903-13-paulmck@kernel.org> (raw)
In-Reply-To: <20220419000315.GA3948789@paulmck-ThinkPad-P17-Gen-1>
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>
---
kernel/rcu/srcutree.c | 62 ++++++++++++++++++++++++-------------------
1 file changed, 34 insertions(+), 28 deletions(-)
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 9dd048989027..b7138dbe1a2d 100644
--- 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);
}
--
2.31.1.189.g2e36527f23
next prev parent reply other threads:[~2022-04-19 0:03 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-19 0:03 [PATCH rcu 0/21] SRCU updates for v5.19 Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 01/21] srcu: Tighten cleanup_srcu_struct() GP checks Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 02/21] srcu: Fix s/is/if/ typo in srcu_node comment Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 03/21] srcu: Make srcu_funnel_gp_start() cache ->mynode in snp_leaf Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 04/21] srcu: Make Tree SRCU able to operate without snp_node array Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 05/21] srcu: Dynamically allocate srcu_node array Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 06/21] srcu: Add size-state transitioning code Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 07/21] srcu: Make rcutorture dump the SRCU size state Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 08/21] srcu: Compute snp_seq earlier in srcu_funnel_gp_start() Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 09/21] srcu: Use invalid initial value for srcu_node GP sequence numbers Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 10/21] srcu: Ensure snp nodes tree is fully initialized before traversal Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 11/21] srcu: Add boot-time control over srcu_node array allocation Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 12/21] srcu: Use export for srcu_struct defined by DEFINE_STATIC_SRCU() Paul E. McKenney
2022-04-19 0:03 ` Paul E. McKenney [this message]
2022-04-19 0:03 ` [PATCH rcu 14/21] srcu: Prevent cleanup_srcu_struct() from freeing non-dynamic ->sda Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 15/21] srcu: Explain srcu_funnel_gp_start() call to list_add() is safe Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 16/21] srcu: Create concurrency-safe helper for initiating size transition Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 17/21] srcu: Add contention-triggered addition of srcu_node tree Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 18/21] srcu: Automatically determine size-transition strategy at boot Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 19/21] srcu: Add contention check to call_srcu() srcu_data ->lock acquisition Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 20/21] srcu: Prevent expedited GPs and blocking readers from consuming CPU Paul E. McKenney
2022-04-19 0:03 ` [PATCH rcu 21/21] srcu: Drop needless initialization of sdp in srcu_gp_start() Paul E. McKenney
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