linux-kernel - [PATCH rcu 2/3] rcu: Stop stall warning from dumping stacks if grace period ends

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20241009180509.778133-2-paulmck@kernel.org>
Date: Wed,  9 Oct 2024 11:05:08 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: frederic@...nel.org,
	rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	rostedt@...dmis.org,
	"Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 2/3] rcu: Stop stall warning from dumping stacks if grace period ends

Currently, once an RCU CPU stall warning decides to dump the stalling
CPUs' stacks, the rcu_dump_cpu_stacks() function persists until it
has gone through the full list.  Unfortunately, if the stalled grace
periods ends midway through, this function will be dumping stacks of
innocent-bystander CPUs that happen to be blocking not the old grace
period, but instead the new one.  This can cause serious confusion.

This commit therefore stops dumping stacks if and when the stalled grace
period ends.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tree_stall.h | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index d7cdd535e50b1..9d79133377ff6 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -335,13 +335,17 @@ static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags)
  * that don't support NMI-based stack dumps.  The NMI-triggered stack
  * traces are more accurate because they are printed by the target CPU.
  */
-static void rcu_dump_cpu_stacks(void)
+static void rcu_dump_cpu_stacks(unsigned long gp_seq)
 {
 	int cpu;
 	unsigned long flags;
 	struct rcu_node *rnp;
 
 	rcu_for_each_leaf_node(rnp) {
+		if (gp_seq != rcu_state.gp_seq) {
+			pr_err("INFO: Stall ended during stack backtracing.\n");
+			return;
+		}
 		printk_deferred_enter();
 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
 		for_each_leaf_node_possible_cpu(rnp, cpu)
@@ -608,7 +612,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 	       (long)rcu_seq_current(&rcu_state.gp_seq), totqlen,
 	       data_race(rcu_state.n_online_cpus)); // Diagnostic read
 	if (ndetected) {
-		rcu_dump_cpu_stacks();
+		rcu_dump_cpu_stacks(gp_seq);
 
 		/* Complain about tasks blocking the grace period. */
 		rcu_for_each_leaf_node(rnp)
@@ -640,7 +644,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 	rcu_force_quiescent_state();  /* Kick them all. */
 }
 
-static void print_cpu_stall(unsigned long gps)
+static void print_cpu_stall(unsigned long gp_seq, unsigned long gps)
 {
 	int cpu;
 	unsigned long flags;
@@ -677,7 +681,7 @@ static void print_cpu_stall(unsigned long gps)
 	rcu_check_gp_kthread_expired_fqs_timer();
 	rcu_check_gp_kthread_starvation();
 
-	rcu_dump_cpu_stacks();
+	rcu_dump_cpu_stacks(gp_seq);
 
 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
 	/* Rewrite if needed in case of slow consoles. */
@@ -759,7 +763,8 @@ static void check_cpu_stall(struct rcu_data *rdp)
 	gs2 = READ_ONCE(rcu_state.gp_seq);
 	if (gs1 != gs2 ||
 	    ULONG_CMP_LT(j, js) ||
-	    ULONG_CMP_GE(gps, js))
+	    ULONG_CMP_GE(gps, js) ||
+	    !rcu_seq_state(gs2))
 		return; /* No stall or GP completed since entering function. */
 	rnp = rdp->mynode;
 	jn = jiffies + ULONG_MAX / 2;
@@ -780,7 +785,7 @@ static void check_cpu_stall(struct rcu_data *rdp)
 			pr_err("INFO: %s detected stall, but suppressed full report due to a stuck CSD-lock.\n", rcu_state.name);
 		} else if (self_detected) {
 			/* We haven't checked in, so go dump stack. */
-			print_cpu_stall(gps);
+			print_cpu_stall(gs2, gps);
 		} else {
 			/* They had a few time units to dump stack, so complain. */
 			print_other_cpu_stall(gs2, gps);
-- 
2.40.1