[PATCH net-next v3 1/2] lockdep: Introduce in_softirq lockdep assert

[Yunsheng Lin]

The current semantic for napi_consume_skb() is that caller need
to provide non-zero budget when calling from NAPI context, and
breaking this semantic will cause hard to debug problem, because
_kfree_skb_defer() need to run in atomic context in order to push
the skb to the particular cpu' napi_alloc_cache atomically.

So add the lockdep_assert_in_softirq() to assert when the running
context is not in_softirq, in_softirq means softirq is serving or
BH is disabled, which has a ambiguous semantics due to the BH
disabled confusion, so add a comment to emphasize that.

And the softirq context can be interrupted by hard IRQ or NMI
context, lockdep_assert_in_softirq() need to assert about hard
IRQ or NMI context too.

Suggested-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx>
---
V3: add comment to emphasize the ambiguous semantics.
---
 include/linux/lockdep.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index f559487..8d60f46 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -594,6 +594,13 @@ do {									\
 		      this_cpu_read(hardirqs_enabled)));		\
 } while (0)
 
+/* Much like in_softirq() - semantics are ambiguous, use carefully. */
+#define lockdep_assert_in_softirq()					\
+do {									\
+	WARN_ON_ONCE(__lockdep_enabled			&&		\
+		     (!in_softirq() || in_irq() || in_nmi()));		\
+} while (0)
+
 #else
 # define might_lock(lock) do { } while (0)
 # define might_lock_read(lock) do { } while (0)
@@ -605,6 +612,7 @@ 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)
 #endif
 
 #ifdef CONFIG_PROVE_RAW_LOCK_NESTING
-- 
2.8.1