unimore/kernel-hacking-2024-linux-steffo
unimore/kernel-hacking-2024-linux-steffo
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locking/local_lock: Add local nested BH locking infrastructure.

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Add local_lock_nested_bh() locking. It is based on local_lock_t and the
naming follows the preempt_disable_nested() example.

For !PREEMPT_RT + !LOCKDEP it is a per-CPU annotation for locking
assumptions based on local_bh_disable(). The macro is optimized away
during compilation.
For !PREEMPT_RT + LOCKDEP the local_lock_nested_bh() is reduced to
the usual lock-acquire plus lockdep_assert_in_softirq() - ensuring that
BH is disabled.

For PREEMPT_RT local_lock_nested_bh() acquires the specified per-CPU
lock. It does not disable CPU migration because it relies on
local_bh_disable() disabling CPU migration.
With LOCKDEP it performans the usual lockdep checks as with !PREEMPT_RT.
Due to include hell the softirq check has been moved spinlock.c.

The intention is to use this locking in places where locking of a per-CPU
variable relies on BH being disabled. Instead of treating disabled
bottom halves as a big per-CPU lock, PREEMPT_RT can use this to reduce
the locking scope to what actually needs protecting.
A side effect is that it also documents the protection scope of the
per-CPU variables.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20240620132727.660738-3-bigeasy@linutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Sebastian Andrzej Siewior 2024-06-20 15:21:52 +02:00 committed by Jakub Kicinski
parent 07e4fd4c05
commit c5bcab7558
4 changed files with 52 additions and 0 deletions
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10
include/linux/local_lock.h
View file

@ -62,4 +62,14 @@ DEFINE_LOCK_GUARD_1(local_lock_irqsave, local_lock_t __percpu,
local_unlock_irqrestore(_T->lock, _T->flags),
unsigned long flags)
#define local_lock_nested_bh(_lock) \
__local_lock_nested_bh(_lock)
#define local_unlock_nested_bh(_lock) \
__local_unlock_nested_bh(_lock)
DEFINE_GUARD(local_lock_nested_bh, local_lock_t __percpu*,
local_lock_nested_bh(_T),
local_unlock_nested_bh(_T))
#endif

31
include/linux/local_lock_internal.h
View file

@ -62,6 +62,17 @@ do { \
local_lock_debug_init(lock); \
} while (0)
#define __spinlock_nested_bh_init(lock) \
do { \
static struct lock_class_key __key; \
\
debug_check_no_locks_freed((void *)lock, sizeof(*lock));\
lockdep_init_map_type(&(lock)->dep_map, #lock, &__key, \
0, LD_WAIT_CONFIG, LD_WAIT_INV, \
LD_LOCK_NORMAL); \
local_lock_debug_init(lock); \
} while (0)
#define __local_lock(lock) \
do { \
preempt_disable(); \
@ -98,6 +109,15 @@ do { \
local_irq_restore(flags); \
} while (0)
#define __local_lock_nested_bh(lock) \
do { \
lockdep_assert_in_softirq(); \
local_lock_acquire(this_cpu_ptr(lock)); \
} while (0)
#define __local_unlock_nested_bh(lock) \
local_lock_release(this_cpu_ptr(lock))
#else /* !CONFIG_PREEMPT_RT */
/*
@ -138,4 +158,15 @@ typedef spinlock_t local_lock_t;
#define __local_unlock_irqrestore(lock, flags) __local_unlock(lock)
#define __local_lock_nested_bh(lock) \
do { \
lockdep_assert_in_softirq_func(); \
spin_lock(this_cpu_ptr(lock)); \
} while (0)
#define __local_unlock_nested_bh(lock) \
do { \
spin_unlock(this_cpu_ptr((lock))); \
} while (0)
#endif /* CONFIG_PREEMPT_RT */

3
include/linux/lockdep.h
View file

@ -600,6 +600,8 @@ do { \
(!in_softirq() || in_irq() || in_nmi())); \
} while (0)
extern void lockdep_assert_in_softirq_func(void);
#else
# define might_lock(lock) do { } while (0)
# define might_lock_read(lock) do { } while (0)
@ -613,6 +615,7 @@ do { \
# define lockdep_assert_preemption_enabled() do { } while (0)
# define lockdep_assert_preemption_disabled() do { } while (0)
# define lockdep_assert_in_softirq() do { } while (0)
# define lockdep_assert_in_softirq_func() do { } while (0)
#endif
#ifdef CONFIG_PROVE_RAW_LOCK_NESTING

8
kernel/locking/spinlock.c
View file

@ -413,3 +413,11 @@ notrace int in_lock_functions(unsigned long addr)
&& addr < (unsigned long)__lock_text_end;
}
EXPORT_SYMBOL(in_lock_functions);
#if defined(CONFIG_PROVE_LOCKING) && defined(CONFIG_PREEMPT_RT)
void notrace lockdep_assert_in_softirq_func(void)
{
lockdep_assert_in_softirq();
}
EXPORT_SYMBOL(lockdep_assert_in_softirq_func);
#endif