summaryrefslogtreecommitdiffstats
path: root/debian/patches-rt/0070-notifier-Make-atomic_notifiers-use-raw_spinlock.patch
blob: 74ee5109b51dd6773622fca618f295864fed9bd4 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
From f603fbc6eaf37d836e3498b47cef43965730bcda Mon Sep 17 00:00:00 2001
From: Valentin Schneider <valentin.schneider@arm.com>
Date: Sun, 22 Nov 2020 20:19:04 +0000
Subject: [PATCH 070/323] notifier: Make atomic_notifiers use raw_spinlock
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz

Booting a recent PREEMPT_RT kernel (v5.10-rc3-rt7-rebase) on my arm64 Juno
leads to the idle task blocking on an RT sleeping spinlock down some
notifier path:

  [    1.809101] BUG: scheduling while atomic: swapper/5/0/0x00000002
  [    1.809116] Modules linked in:
  [    1.809123] Preemption disabled at:
  [    1.809125] secondary_start_kernel (arch/arm64/kernel/smp.c:227)
  [    1.809146] CPU: 5 PID: 0 Comm: swapper/5 Tainted: G        W         5.10.0-rc3-rt7 #168
  [    1.809153] Hardware name: ARM Juno development board (r0) (DT)
  [    1.809158] Call trace:
  [    1.809160] dump_backtrace (arch/arm64/kernel/stacktrace.c:100 (discriminator 1))
  [    1.809170] show_stack (arch/arm64/kernel/stacktrace.c:198)
  [    1.809178] dump_stack (lib/dump_stack.c:122)
  [    1.809188] __schedule_bug (kernel/sched/core.c:4886)
  [    1.809197] __schedule (./arch/arm64/include/asm/preempt.h:18 kernel/sched/core.c:4913 kernel/sched/core.c:5040)
  [    1.809204] preempt_schedule_lock (kernel/sched/core.c:5365 (discriminator 1))
  [    1.809210] rt_spin_lock_slowlock_locked (kernel/locking/rtmutex.c:1072)
  [    1.809217] rt_spin_lock_slowlock (kernel/locking/rtmutex.c:1110)
  [    1.809224] rt_spin_lock (./include/linux/rcupdate.h:647 kernel/locking/rtmutex.c:1139)
  [    1.809231] atomic_notifier_call_chain_robust (kernel/notifier.c:71 kernel/notifier.c:118 kernel/notifier.c:186)
  [    1.809240] cpu_pm_enter (kernel/cpu_pm.c:39 kernel/cpu_pm.c:93)
  [    1.809249] psci_enter_idle_state (drivers/cpuidle/cpuidle-psci.c:52 drivers/cpuidle/cpuidle-psci.c:129)
  [    1.809258] cpuidle_enter_state (drivers/cpuidle/cpuidle.c:238)
  [    1.809267] cpuidle_enter (drivers/cpuidle/cpuidle.c:353)
  [    1.809275] do_idle (kernel/sched/idle.c:132 kernel/sched/idle.c:213 kernel/sched/idle.c:273)
  [    1.809282] cpu_startup_entry (kernel/sched/idle.c:368 (discriminator 1))
  [    1.809288] secondary_start_kernel (arch/arm64/kernel/smp.c:273)

Two points worth noting:

1) That this is conceptually the same issue as pointed out in:
   313c8c16ee62 ("PM / CPU: replace raw_notifier with atomic_notifier")
2) Only the _robust() variant of atomic_notifier callchains suffer from
   this

AFAICT only the cpu_pm_notifier_chain really needs to be changed, but
singling it out would mean introducing a new (truly) non-blocking API. At
the same time, callers that are fine with any blocking within the call
chain should use blocking notifiers, so patching up all atomic_notifier's
doesn't seem *too* crazy to me.

Fixes: 70d932985757 ("notifier: Fix broken error handling pattern")
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Link: https://lkml.kernel.org/r/20201122201904.30940-1-valentin.schneider@arm.com
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/notifier.h |  6 +++---
 kernel/notifier.c        | 12 ++++++------
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index 2fb373a5c1ed..723bc2df6388 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -58,7 +58,7 @@ struct notifier_block {
 };
 
 struct atomic_notifier_head {
-	spinlock_t lock;
+	raw_spinlock_t lock;
 	struct notifier_block __rcu *head;
 };
 
@@ -78,7 +78,7 @@ struct srcu_notifier_head {
 };
 
 #define ATOMIC_INIT_NOTIFIER_HEAD(name) do {	\
-		spin_lock_init(&(name)->lock);	\
+		raw_spin_lock_init(&(name)->lock);	\
 		(name)->head = NULL;		\
 	} while (0)
 #define BLOCKING_INIT_NOTIFIER_HEAD(name) do {	\
@@ -95,7 +95,7 @@ extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
 		cleanup_srcu_struct(&(name)->srcu);
 
 #define ATOMIC_NOTIFIER_INIT(name) {				\
-		.lock = __SPIN_LOCK_UNLOCKED(name.lock),	\
+		.lock = __RAW_SPIN_LOCK_UNLOCKED(name.lock),	\
 		.head = NULL }
 #define BLOCKING_NOTIFIER_INIT(name) {				\
 		.rwsem = __RWSEM_INITIALIZER((name).rwsem),	\
diff --git a/kernel/notifier.c b/kernel/notifier.c
index 1b019cbca594..c20782f07643 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -142,9 +142,9 @@ int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
 	unsigned long flags;
 	int ret;
 
-	spin_lock_irqsave(&nh->lock, flags);
+	raw_spin_lock_irqsave(&nh->lock, flags);
 	ret = notifier_chain_register(&nh->head, n);
-	spin_unlock_irqrestore(&nh->lock, flags);
+	raw_spin_unlock_irqrestore(&nh->lock, flags);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(atomic_notifier_chain_register);
@@ -164,9 +164,9 @@ int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
 	unsigned long flags;
 	int ret;
 
-	spin_lock_irqsave(&nh->lock, flags);
+	raw_spin_lock_irqsave(&nh->lock, flags);
 	ret = notifier_chain_unregister(&nh->head, n);
-	spin_unlock_irqrestore(&nh->lock, flags);
+	raw_spin_unlock_irqrestore(&nh->lock, flags);
 	synchronize_rcu();
 	return ret;
 }
@@ -182,9 +182,9 @@ int atomic_notifier_call_chain_robust(struct atomic_notifier_head *nh,
 	 * Musn't use RCU; because then the notifier list can
 	 * change between the up and down traversal.
 	 */
-	spin_lock_irqsave(&nh->lock, flags);
+	raw_spin_lock_irqsave(&nh->lock, flags);
 	ret = notifier_call_chain_robust(&nh->head, val_up, val_down, v);
-	spin_unlock_irqrestore(&nh->lock, flags);
+	raw_spin_unlock_irqrestore(&nh->lock, flags);
 
 	return ret;
 }
-- 
2.43.0