[PATCH] lockdep: Fix subclass resource leak in lockdep_unregister_key()

[Nilay Shroff]

When a dynamic lock key is unregistered using lockdep_unregister_key(),
lockdep routes the cleanup sequence through __lockdep_free_key_range()
with a hardcoded size of 1.

This layout model assumes that a dynamic key only occupies its base
registration address (subclass 0). However, when a lock utilizes
nested acquisitions—either implicitly via networking paths (e.g.,
bh_lock_sock_nested() passing SINGLE_DEPTH_NESTING) or explicitly via
mutex_lock_nested()—lockdep calculates virtual class tracking nodes
using pointer math offsets:

    Virtual Class Pointer = Base Address of Key + Subclass Index

Because the unregister range size is strictly constrained to 1, lockdep
completely skips evaluating adjacent virtual subclass slots (key + 1
through key + 7). Consequently, when dynamic structures (such as per-
queue network sockets) are repeatedly created, teardowned, and allocated
at fresh memory blocks, the subclass /1 structures and their historical
dependency chains are permanently orphaned in the global graph. Over
prolonged runtime and frequent reconnect loops, this asymmetry leads to
the absolute exhaustion of MAX_LOCKDEP_CHAIN_HLOCKS.

Fix this by instructing lockdep_unregister_key() to look ahead across
the entire valid subclass allocation block range
(MAX_LOCKDEP_SUBCLASSES), ensuring that all related subclass matrix
definitions are completely zapped alongside the primary key.

Cc: Shin'ichiro Kawasaki <shinichiro.kawasaki@xxxxxxx>
Reported-by: Geliang Tang <geliang@xxxxxxxxxx>
Tested-by: Geliang Tang <geliang@xxxxxxxxxx>
Signed-off-by: Nilay Shroff <nilay@xxxxxxxxxxxxx>
---
 kernel/locking/lockdep.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 2d4c5bab5af8..490904bee63e 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -6606,7 +6606,7 @@ void lockdep_unregister_key(struct lock_class_key *key)
 	WARN_ON_ONCE(!found && debug_locks);
 	if (found) {
 		pf = get_pending_free();
-		__lockdep_free_key_range(pf, key, 1);
+		__lockdep_free_key_range(pf, key, MAX_LOCKDEP_SUBCLASSES);
 		need_callback = prepare_call_rcu_zapped(pf);
 		nr_dynamic_keys--;
 	}
-- 
2.53.0