linux-kernel - [PATCH] rcutorture: Fix rcutorture_one_extend

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Message-Id: <20250507112605.20910-1-qiang.zhang1211@gmail.com>
Date: Wed,  7 May 2025 19:26:03 +0800
From: Zqiang <qiang.zhang1211@...il.com>
To: paulmck@...nel.org,
	frederic@...nel.org,
	neeraj.upadhyay@...nel.org,
	joel@...lfernandes.org,
	urezki@...il.com,
	boqun.feng@...il.com
Cc: qiang.zhang1211@...il.com,
	rcu@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] rcutorture: Fix rcutorture_one_extend_check() splat in RT kernels

For built with CONFIG_PREEMPT_RT=y kernels, running rcutorture
tests resulted in the following splat:

[   68.797425] rcutorture_one_extend_check during change: Current 0x1  To add 0x1  To remove 0x0  preempt_count() 0x0
[   68.797533] WARNING: CPU: 2 PID: 512 at kernel/rcu/rcutorture.c:1993 rcutorture_one_extend_check+0x419/0x560 [rcutorture]
[   68.797601] Call Trace:
[   68.797602]  <TASK>
[   68.797619]  ? lockdep_softirqs_off+0xa5/0x160
[   68.797631]  rcutorture_one_extend+0x18e/0xcc0 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c]
[   68.797646]  ? local_clock+0x19/0x40
[   68.797659]  rcu_torture_one_read+0xf0/0x280 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c]
[   68.797678]  ? __pfx_rcu_torture_one_read+0x10/0x10 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c]
[   68.797804]  ? __pfx_rcu_torture_timer+0x10/0x10 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c]
[   68.797815] rcu-torture: rcu_torture_reader task started
[   68.797824] rcu-torture: Creating rcu_torture_reader task
[   68.797824]  rcu_torture_reader+0x238/0x580 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c]
[   68.797836]  ? kvm_sched_clock_read+0x15/0x30

Disable BH does not change the SOFTIRQ corresponding bits in
preempt_count() for RT kernels, this commit therefore use
softirq_count() to check the if BH is disabled.

Signed-off-by: Zqiang <qiang.zhang1211@...il.com>
---
 kernel/rcu/rcutorture.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 373c65a6e103..ef439569f979 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -471,7 +471,7 @@ rcu_read_delay(struct torture_random_state *rrsp, struct rt_read_seg *rtrsp)
 	    !(torture_random(rrsp) % (nrealreaders * 2000 * longdelay_ms))) {
 		started = cur_ops->get_gp_seq();
 		ts = rcu_trace_clock_local();
-		if (preempt_count() & (SOFTIRQ_MASK | HARDIRQ_MASK))
+		if ((preempt_count() & HARDIRQ_MASK) || softirq_count())
 			longdelay_ms = 5; /* Avoid triggering BH limits. */
 		mdelay(longdelay_ms);
 		rtrsp->rt_delay_ms = longdelay_ms;
@@ -1990,7 +1990,7 @@ static void rcutorture_one_extend_check(char *s, int curstate, int new, int old,
 		return;
 
 	WARN_ONCE((curstate & (RCUTORTURE_RDR_BH | RCUTORTURE_RDR_RBH)) &&
-		  !(preempt_count() & SOFTIRQ_MASK), ROEC_ARGS);
+		  !softirq_count(), ROEC_ARGS);
 	WARN_ONCE((curstate & (RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED)) &&
 		  !(preempt_count() & PREEMPT_MASK), ROEC_ARGS);
 	WARN_ONCE(cur_ops->readlock_nesting &&
@@ -2004,7 +2004,7 @@ static void rcutorture_one_extend_check(char *s, int curstate, int new, int old,
 
 	WARN_ONCE(cur_ops->extendables &&
 		  !(curstate & (RCUTORTURE_RDR_BH | RCUTORTURE_RDR_RBH)) &&
-		  (preempt_count() & SOFTIRQ_MASK), ROEC_ARGS);
+		  softirq_count(), ROEC_ARGS);
 
 	/*
 	 * non-preemptible RCU in a preemptible kernel uses preempt_disable()
@@ -2025,6 +2025,9 @@ static void rcutorture_one_extend_check(char *s, int curstate, int new, int old,
 	if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
 		mask |= RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED;
 
+	if (IS_ENABLED(CONFIG_PREEMPT_RT) && softirq_count())
+		mask |= RCUTORTURE_RDR_BH | RCUTORTURE_RDR_RBH;
+
 	WARN_ONCE(cur_ops->readlock_nesting && !(curstate & mask) &&
 		  cur_ops->readlock_nesting() > 0, ROEC_ARGS);
 }
-- 
2.17.1