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authorPeter Zijlstra <peterz@infradead.org>2020-02-20 09:45:02 +0100
committerPeter Zijlstra <peterz@infradead.org>2020-03-20 13:06:25 +0100
commitf6f48e18040402136874a6a71611e081b4d0788a (patch)
tree494c4d17ab3f9744cc60647470b10ff45aefaf47 /kernel/locking
parent248efb2158f1e23750728e92ad9db3ab60c14485 (diff)
lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions
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
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/lockdep.c62
1 files changed, 59 insertions, 3 deletions
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 47e3acb6b5c9..4c3b1ccc6c2d 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -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);