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Date:   Mon, 9 Aug 2021 15:59:09 -0500
From:   Clark Williams <williams@redhat.com>
To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org
Subject: [PATCH PREEMPT_RT] kcov:  fix locking splat from
 kcov_remote_start()
Message-ID: <20210809155909.333073de@theseus.lan>
Organization: Red Hat, Inc
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Precedence: bulk

Saw the following splat on 5.14-rc4-rt5 with:

CONFIG_KCOV=y
CONFIG_KCOV_INSTRUMENT_ALL=y
CONFIG_KCOV_IRQ_AREA_SIZE=0x40000
CONFIG_RUNTIME_TESTING_MENU=y

kernel: ehci-pci 0000:00:1d.0: USB 2.0 started, EHCI 1.00
kernel: BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:35
kernel: in_atomic(): 0, irqs_disabled(): 1, non_block: 0, pid: 34, name: ksoftirqd/3
kernel: 4 locks held by ksoftirqd/3/34:
kernel:  #0: ffff944376d989f8 ((softirq_ctrl.lock).lock){+.+.}-{2:2}, at: __local_bh_disable_ip+0xe0/0x190
kernel:  #1: ffffffffbbfb61e0 (rcu_read_lock){....}-{1:2}, at: rt_spin_lock+0x5/0xd0
kernel:  #2: ffffffffbbfb61e0 (rcu_read_lock){....}-{1:2}, at: __local_bh_disable_ip+0xbd/0x190
kernel:  #3: ffffffffbc086518 (kcov_remote_lock){....}-{2:2}, at: kcov_remote_start+0x119/0x4a0
kernel: irq event stamp: 4653
kernel: hardirqs last  enabled at (4652): [<ffffffffbafb85ce>] _raw_spin_unlock_irqrestore+0x6e/0x80
kernel: hardirqs last disabled at (4653): [<ffffffffba2517c8>] kcov_remote_start+0x298/0x4a0
kernel: softirqs last  enabled at (4638): [<ffffffffba110a5b>] run_ksoftirqd+0x9b/0x100
kernel: softirqs last disabled at (4644): [<ffffffffba149f12>] smpboot_thread_fn+0x2b2/0x410
kernel: CPU: 3 PID: 34 Comm: ksoftirqd/3 Not tainted 5.14.0-rc4-rt5+ #3
kernel: Hardware name:  /NUC5i7RYB, BIOS RYBDWi35.86A.0359.2016.0906.1028 09/06/2016
kernel: Call Trace:
kernel:  dump_stack_lvl+0x7a/0x9b
kernel:  ___might_sleep.cold+0xf3/0x107
kernel:  rt_spin_lock+0x3a/0xd0
kernel:  ? kcov_remote_start+0x119/0x4a0
kernel:  kcov_remote_start+0x119/0x4a0
kernel:  ? led_trigger_blink_oneshot+0x83/0xa0
kernel:  __usb_hcd_giveback_urb+0x161/0x1e0
kernel:  usb_giveback_urb_bh+0xb6/0x110
kernel:  tasklet_action_common.constprop.0+0xe8/0x110
kernel:  __do_softirq+0xe2/0x525
kernel:  ? smpboot_thread_fn+0x31/0x410
kernel:  run_ksoftirqd+0x8c/0x100
kernel:  smpboot_thread_fn+0x2b2/0x410
kernel:  ? smpboot_register_percpu_thread+0x130/0x130
kernel:  kthread+0x1de/0x210
kernel:  ? set_kthread_struct+0x60/0x60
kernel:  ret_from_fork+0x22/0x30
kernel: usb usb1: New USB device found, idVendor=1d6b, idProduct=0002, bcdDevice= 5.14


Change kcov_remote_lock from regular spinlock_t to raw_spinlock_t so that
we don't get "sleeping function called from invalid context" on PREEMPT_RT kernel.

Signed-off-by: Clark Williams <williams@redhat.com>
---
 kernel/kcov.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 80bfe71bbe13..60f903f8a46c 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -82,7 +82,7 @@ struct kcov_remote {
 	struct hlist_node	hnode;
 };
 
-static DEFINE_SPINLOCK(kcov_remote_lock);
+static DEFINE_RAW_SPINLOCK(kcov_remote_lock);
 static DEFINE_HASHTABLE(kcov_remote_map, 4);
 static struct list_head kcov_remote_areas = LIST_HEAD_INIT(kcov_remote_areas);
 
@@ -375,7 +375,7 @@ static void kcov_remote_reset(struct kcov *kcov)
 	struct hlist_node *tmp;
 	unsigned long flags;
 
-	spin_lock_irqsave(&kcov_remote_lock, flags);
+	raw_spin_lock_irqsave(&kcov_remote_lock, flags);
 	hash_for_each_safe(kcov_remote_map, bkt, tmp, remote, hnode) {
 		if (remote->kcov != kcov)
 			continue;
@@ -384,7 +384,7 @@ static void kcov_remote_reset(struct kcov *kcov)
 	}
 	/* Do reset before unlock to prevent races with kcov_remote_start(). */
 	kcov_reset(kcov);
-	spin_unlock_irqrestore(&kcov_remote_lock, flags);
+	raw_spin_unlock_irqrestore(&kcov_remote_lock, flags);
 }
 
 static void kcov_disable(struct task_struct *t, struct kcov *kcov)
@@ -638,18 +638,18 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
 		kcov->t = t;
 		kcov->remote = true;
 		kcov->remote_size = remote_arg->area_size;
-		spin_lock_irqsave(&kcov_remote_lock, flags);
+		raw_spin_lock_irqsave(&kcov_remote_lock, flags);
 		for (i = 0; i < remote_arg->num_handles; i++) {
 			if (!kcov_check_handle(remote_arg->handles[i],
 						false, true, false)) {
-				spin_unlock_irqrestore(&kcov_remote_lock,
+				raw_spin_unlock_irqrestore(&kcov_remote_lock,
 							flags);
 				kcov_disable(t, kcov);
 				return -EINVAL;
 			}
 			remote = kcov_remote_add(kcov, remote_arg->handles[i]);
 			if (IS_ERR(remote)) {
-				spin_unlock_irqrestore(&kcov_remote_lock,
+				raw_spin_unlock_irqrestore(&kcov_remote_lock,
 							flags);
 				kcov_disable(t, kcov);
 				return PTR_ERR(remote);
@@ -658,7 +658,7 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
 		if (remote_arg->common_handle) {
 			if (!kcov_check_handle(remote_arg->common_handle,
 						true, false, false)) {
-				spin_unlock_irqrestore(&kcov_remote_lock,
+				raw_spin_unlock_irqrestore(&kcov_remote_lock,
 							flags);
 				kcov_disable(t, kcov);
 				return -EINVAL;
@@ -666,14 +666,14 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
 			remote = kcov_remote_add(kcov,
 					remote_arg->common_handle);
 			if (IS_ERR(remote)) {
-				spin_unlock_irqrestore(&kcov_remote_lock,
+				raw_spin_unlock_irqrestore(&kcov_remote_lock,
 							flags);
 				kcov_disable(t, kcov);
 				return PTR_ERR(remote);
 			}
 			t->kcov_handle = remote_arg->common_handle;
 		}
-		spin_unlock_irqrestore(&kcov_remote_lock, flags);
+		raw_spin_unlock_irqrestore(&kcov_remote_lock, flags);
 		/* Put either in kcov_task_exit() or in KCOV_DISABLE. */
 		kcov_get(kcov);
 		return 0;
@@ -845,10 +845,10 @@ void kcov_remote_start(u64 handle)
 		return;
 	}
 
-	spin_lock(&kcov_remote_lock);
+	raw_spin_lock(&kcov_remote_lock);
 	remote = kcov_remote_find(handle);
 	if (!remote) {
-		spin_unlock_irqrestore(&kcov_remote_lock, flags);
+		raw_spin_unlock_irqrestore(&kcov_remote_lock, flags);
 		return;
 	}
 	kcov_debug("handle = %llx, context: %s\n", handle,
@@ -869,7 +869,7 @@ void kcov_remote_start(u64 handle)
 		size = CONFIG_KCOV_IRQ_AREA_SIZE;
 		area = this_cpu_ptr(&kcov_percpu_data)->irq_area;
 	}
-	spin_unlock_irqrestore(&kcov_remote_lock, flags);
+	raw_spin_unlock_irqrestore(&kcov_remote_lock, flags);
 
 	/* Can only happen when in_task(). */
 	if (!area) {
@@ -1008,9 +1008,9 @@ void kcov_remote_stop(void)
 	spin_unlock(&kcov->lock);
 
 	if (in_task()) {
-		spin_lock(&kcov_remote_lock);
+		raw_spin_lock(&kcov_remote_lock);
 		kcov_remote_area_put(area, size);
-		spin_unlock(&kcov_remote_lock);
+		raw_spin_unlock(&kcov_remote_lock);
 	}
 
 	local_irq_restore(flags);
-- 
2.31.1


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