[PATCH] mm: vmalloc: annotate find_vmap_area_exceed_addr_lock() for lockdep

[Jens Axboe <axboe@kernel.dk>]

lockdep gets confused with the nested locking:

============================================
WARNING: possible recursive locking detected
6.9.0-rc1-00060-ged3ccc57b108-dirty #6140 Not tainted
--------------------------------------------
drgn/455 is trying to acquire lock:
ffff0000c00131d0 (&vn->busy.lock/1){+.+.}-{2:2}, at: find_vmap_area_exceed_addr_lock+0x64/0x124

but task is already holding lock:
ffff0000c0011878 (&vn->busy.lock/1){+.+.}-{2:2}, at: find_vmap_area_exceed_addr_lock+0x64/0x124

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&vn->busy.lock/1);
  lock(&vn->busy.lock/1);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by drgn/455:
 #0: ffff800081ecbba8 (kclist_lock){++++}-{3:3}, at: read_kcore_iter+0x5c/0xa24
 #1: ffff800081ea7688 (page_offline_rwsem){.+.+}-{3:3}, at: page_offline_freeze+0x14/0x1c
 #2: ffff0000c0011878 (&vn->busy.lock/1){+.+.}-{2:2}, at: find_vmap_area_exceed_addr_lock+0x64/0x124

stack backtrace:
CPU: 5 PID: 455 Comm: drgn Not tainted 6.9.0-rc1-00060-ged3ccc57b108-dirty #6140
Hardware name: linux,dummy-virt (DT)
Call trace:
 dump_backtrace+0x90/0xe4
 show_stack+0x14/0x1c
 dump_stack_lvl+0x84/0xc0
 dump_stack+0x14/0x1c
 print_deadlock_bug+0x24c/0x334
 __lock_acquire+0xdf4/0x20e0
 lock_acquire+0x204/0x330
 _raw_spin_lock_nested+0x40/0x54
 find_vmap_area_exceed_addr_lock+0x64/0x124
 vread_iter+0x44/0x428
 read_kcore_iter+0x170/0xa24
 proc_reg_read_iter+0x7c/0xcc
 vfs_read+0x220/0x2c4
 ksys_pread64+0x74/0xb4
 __arm64_sys_pread64+0x1c/0x24
 invoke_syscall+0x44/0x104
 el0_svc_common.constprop.0+0xb4/0xd4
 do_el0_svc+0x18/0x20
 el0_svc+0x44/0x108
 el0t_64_sync_handler+0x118/0x124
 el0t_64_sync+0x168/0x16c

which seems to be because it's missing the proper nested annotation.
Add the level annotation to make lockdep happy about this use case.

Fixes: 53becf32aec1 ("mm: vmalloc: support multiple nodes in vread_iter")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

---

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 22aa63f4ef63..26a69fa6809c 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1032,7 +1032,7 @@ find_vmap_area_exceed_addr_lock(unsigned long addr, struct vmap_area **va)
 	for (i = 0; i < nr_vmap_nodes; i++) {
 		vn = &vmap_nodes[i];
 
-		spin_lock(&vn->busy.lock);
+		spin_lock_nested(&vn->busy.lock, i);
 		va_lowest = __find_vmap_area_exceed_addr(addr, &vn->busy.root);
 		if (va_lowest) {
 			if (!va_node || va_lowest->va_start < (*va)->va_start) {
-- 
Jens Axboe