[PATCH v2 5/6] lockdep: Prepare for NMI IRQ state tracking

Peter Zijlstra
2020-05-28T14:17:29Z

There is no reason not to always, accurately, track IRQ state.

This change also makes IRQ state tracking ignore lockdep_off().

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/locking/lockdep.c | 33 ++++++++++++++++++++++++++++++---
1 file changed, 30 insertions(+), 3 deletions(-)

--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3646,7 +3646,13 @@ static void __trace_hardirqs_on_caller(v
*/
void lockdep_hardirqs_on_prepare(unsigned long ip)
{
- if (unlikely(!debug_locks || current->lockdep_recursion))
+ /*
+ * NMIs do not (and cannot) track lock dependencies, nothing to do.
+ */
+ if (in_nmi())
+ return;
+
+ if (DEBUG_LOCKS_WARN_ON(current->lockdep_recursion & LOCKDEP_RECURSION_MASK))
return;

if (unlikely(lockdep_hardirqs_enabled())) {
@@ -3692,7 +3698,24 @@ void noinstr lockdep_hardirqs_on(unsigne
{
struct task_struct *curr = current;

- if (unlikely(!debug_locks || curr->lockdep_recursion))
+ /*
+ * NMIs can happen in the middle of local_irq_{en,dis}able() where the
+ * tracking state and hardware state are out of sync.
+ *
+ * NMIs must save lockdep_hardirqs_enabled() to restore IRQ state from,
+ * and not rely on hardware state like normal interrupts.
+ */
+ if (in_nmi()) {
+ /*
+ * Skip:
+ * - recursion check, because NMI can hit lockdep;
+ * - hardware state check, because above;
+ * - chain_key check, see lockdep_hardirqs_on_prepare().
+ */
+ goto skip_checks;
+ }
+
+ if (DEBUG_LOCKS_WARN_ON(curr->lockdep_recursion & LOCKDEP_RECURSION_MASK))
return;

if (lockdep_hardirqs_enabled()) {
@@ -3720,6 +3743,7 @@ void noinstr lockdep_hardirqs_on(unsigne
DEBUG_LOCKS_WARN_ON(current->hardirq_chain_key !=
current->curr_chain_key);

+skip_checks:
/* we'll do an OFF -> ON transition: */
this_cpu_write(hardirqs_enabled, 1);
curr->hardirq_enable_ip = ip;
@@ -3735,7 +3759,10 @@ void noinstr lockdep_hardirqs_off(unsign
{
struct task_struct *curr = current;

- if (unlikely(!debug_locks || curr->lockdep_recursion))
+ /*
+ * NMIs can happen in lockdep.
+ */
+ if (!in_nmi() && DEBUG_LOCKS_WARN_ON(curr->lockdep_recursion & LOCKDEP_RECURSION_MASK))
return;

/*