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lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions

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nmi_enter() does lockdep_off() and hence lockdep ignores everything.

And NMI context makes it impossible to do full IN-NMI tracking like we
do IN-HARDIRQ, that could result in graph_lock recursion.

However, since look_up_lock_class() is lockless, we can find the class
of a lock that has prior use and detect IN-NMI after USED, just not
USED after IN-NMI.

NOTE: By shifting the lockdep_off() recursion count to bit-16, we can
easily differentiate between actual recursion and off.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Link: https://lkml.kernel.org/r/20200221134215.090538203@infradead.org
This commit is contained in:
Peter Zijlstra 2020-02-20 09:45:02 +01:00
parent 248efb2158
commit f6f48e1804
1 changed files with 59 additions and 3 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

62
kernel/locking/lockdep.c
View file

@ -393,15 +393,22 @@ void lockdep_init_task(struct task_struct *task)
task->lockdep_recursion = 0;
}
/*
* Split the recrursion counter in two to readily detect 'off' vs recursion.
*/
#define LOCKDEP_RECURSION_BITS 16
#define LOCKDEP_OFF (1U << LOCKDEP_RECURSION_BITS)
#define LOCKDEP_RECURSION_MASK (LOCKDEP_OFF - 1)
void lockdep_off(void)
{
current->lockdep_recursion++;
current->lockdep_recursion += LOCKDEP_OFF;
}
EXPORT_SYMBOL(lockdep_off);
void lockdep_on(void)
{
current->lockdep_recursion--;
current->lockdep_recursion -= LOCKDEP_OFF;
}
EXPORT_SYMBOL(lockdep_on);
@ -597,6 +604,7 @@ static const char *usage_str[] =
#include "lockdep_states.h"
#undef LOCKDEP_STATE
[LOCK_USED] = "INITIAL USE",
[LOCK_USAGE_STATES] = "IN-NMI",
};
#endif
@ -809,6 +817,7 @@ static int count_matching_names(struct lock_class *new_class)
return count + 1;
}
/* used from NMI context -- must be lockless */
static inline struct lock_class *
look_up_lock_class(const struct lockdep_map *lock, unsigned int subclass)
{
@ -4720,6 +4729,36 @@ void lock_downgrade(struct lockdep_map *lock, unsigned long ip)
}
EXPORT_SYMBOL_GPL(lock_downgrade);
/* NMI context !!! */
static void verify_lock_unused(struct lockdep_map *lock, struct held_lock *hlock, int subclass)
{
#ifdef CONFIG_PROVE_LOCKING
struct lock_class *class = look_up_lock_class(lock, subclass);
/* if it doesn't have a class (yet), it certainly hasn't been used yet */
if (!class)
return;
if (!(class->usage_mask & LOCK_USED))
return;
hlock->class_idx = class - lock_classes;
print_usage_bug(current, hlock, LOCK_USED, LOCK_USAGE_STATES);
#endif
}
static bool lockdep_nmi(void)
{
if (current->lockdep_recursion & LOCKDEP_RECURSION_MASK)
return false;
if (!in_nmi())
return false;
return true;
}
/*
* We are not always called with irqs disabled - do that here,
* and also avoid lockdep recursion:
@ -4730,8 +4769,25 @@ void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
{
unsigned long flags;
if (unlikely(current->lockdep_recursion))
if (unlikely(current->lockdep_recursion)) {
/* XXX allow trylock from NMI ?!? */
if (lockdep_nmi() && !trylock) {
struct held_lock hlock;
hlock.acquire_ip = ip;
hlock.instance = lock;
hlock.nest_lock = nest_lock;
hlock.irq_context = 2; // XXX
hlock.trylock = trylock;
hlock.read = read;
hlock.check = check;
hlock.hardirqs_off = true;
hlock.references = 0;
verify_lock_unused(lock, &hlock, subclass);
}
return;
}
raw_local_irq_save(flags);
check_flags(flags);