[PATCH v3] lockdep: Fix wait context check on softirq for PREEMPT_RT

[Ryo Takakura <ryotkkr98@gmail.com>]

Since commit 0c1d7a2c2d32 ("lockdep: Remove softirq accounting on
PREEMPT_RT."), the wait context test for mutex usage within
"in softirq context" fails as it references @softirq_context.

[    0.184549]   | wait context tests |
[    0.184549]   --------------------------------------------------------------------------
[    0.184549]                                  | rcu  | raw  | spin |mutex |
[    0.184549]   --------------------------------------------------------------------------
[    0.184550]                in hardirq context:  ok  |  ok  |  ok  |  ok  |
[    0.185083] in hardirq context (not threaded):  ok  |  ok  |  ok  |  ok  |
[    0.185606]                in softirq context:  ok  |  ok  |  ok  |FAILED|

As a fix, add lockdep map for BH disabled section. This fixes the
issue by letting us catch cases when local_bh_disable() gets called
with preemption disabled where local_lock doesn't get acquired.
In the case of "in softirq context" selftest, local_bh_disable() was
being called with preemption disable as it's early in the boot.

Signed-off-by: Ryo Takakura <ryotkkr98@gmail.com>
---

Hi!

This version uses CONFIG_DEBUG_LOCK_ALLOC instead of CONFIG_LOCKDEP.
Thanks Waiman for the advise!

v1:
https://lore.kernel.org/lkml/20241202012017.14910-1-ryotkkr98@gmail.com/

v2:
https://lore.kernel.org/lkml/20241227040824.83626-1-ryotkkr98@gmail.com/

Boqun, let me know in case if I should add you as <suggested-by> tag.
(Please forgive me and ignore if not what the tag intends for... 
I thought its appropriate reading the document[0].)

Sincerely,
Ryo Takakura

[0] https://www.kernel.org/doc/html/v6.12/process/submitting-patches.html#using-reported-by-tested-by-reviewed-by-suggested-by-and-fixes

---
 include/linux/bottom_half.h |  8 ++++++++
 kernel/softirq.c            | 12 ++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/include/linux/bottom_half.h b/include/linux/bottom_half.h
index fc53e0ad5..0640a147b 100644
--- a/include/linux/bottom_half.h
+++ b/include/linux/bottom_half.h
@@ -4,6 +4,7 @@
 
 #include <linux/instruction_pointer.h>
 #include <linux/preempt.h>
+#include <linux/lockdep.h>
 
 #if defined(CONFIG_PREEMPT_RT) || defined(CONFIG_TRACE_IRQFLAGS)
 extern void __local_bh_disable_ip(unsigned long ip, unsigned int cnt);
@@ -15,8 +16,13 @@ static __always_inline void __local_bh_disable_ip(unsigned long ip, unsigned int
 }
 #endif
 
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+extern struct lockdep_map bh_lock_map;
+#endif
+
 static inline void local_bh_disable(void)
 {
+	lock_map_acquire_read(&bh_lock_map);
 	__local_bh_disable_ip(_THIS_IP_, SOFTIRQ_DISABLE_OFFSET);
 }
 
@@ -25,11 +31,13 @@ extern void __local_bh_enable_ip(unsigned long ip, unsigned int cnt);
 
 static inline void local_bh_enable_ip(unsigned long ip)
 {
+	lock_map_release(&bh_lock_map);
 	__local_bh_enable_ip(ip, SOFTIRQ_DISABLE_OFFSET);
 }
 
 static inline void local_bh_enable(void)
 {
+	lock_map_release(&bh_lock_map);
 	__local_bh_enable_ip(_THIS_IP_, SOFTIRQ_DISABLE_OFFSET);
 }
 
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 8c4524ce6..f0edb0abc 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -1012,3 +1012,15 @@ unsigned int __weak arch_dynirq_lower_bound(unsigned int from)
 {
 	return from;
 }
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+static struct lock_class_key bh_lock_key;
+struct lockdep_map bh_lock_map = {
+	.name = "local_bh",
+	.key = &bh_lock_key,
+	.wait_type_outer = LD_WAIT_FREE,
+	.wait_type_inner = LD_WAIT_CONFIG, /* PREEMPT_RT makes BH preemptible. */
+	.lock_type = LD_LOCK_PERCPU,
+};
+EXPORT_SYMBOL_GPL(bh_lock_map);
+#endif
-- 
2.34.1