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Subject[PATCH net] tipc: eliminate possible recursive locking detected by LOCKDEP
Date
When booting kernel with LOCKDEP option, below warning info was found:

WARNING: possible recursive locking detected
4.19.0-rc7+ #14 Not tainted
--------------------------------------------
swapper/0/1 is trying to acquire lock:
00000000dcfc0fc8 (&(&list->lock)->rlock#4){+...}, at: spin_lock_bh
include/linux/spinlock.h:334 [inline]
00000000dcfc0fc8 (&(&list->lock)->rlock#4){+...}, at:
tipc_link_reset+0x125/0xdf0 net/tipc/link.c:850

but task is already holding lock:
00000000cbb9b036 (&(&list->lock)->rlock#4){+...}, at: spin_lock_bh
include/linux/spinlock.h:334 [inline]
00000000cbb9b036 (&(&list->lock)->rlock#4){+...}, at:
tipc_link_reset+0xfa/0xdf0 net/tipc/link.c:849

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

CPU0
----
lock(&(&list->lock)->rlock#4);
lock(&(&list->lock)->rlock#4);

*** DEADLOCK ***

May be due to missing lock nesting notation

2 locks held by swapper/0/1:
#0: 00000000f7539d34 (pernet_ops_rwsem){+.+.}, at:
register_pernet_subsys+0x19/0x40 net/core/net_namespace.c:1051
#1: 00000000cbb9b036 (&(&list->lock)->rlock#4){+...}, at:
spin_lock_bh include/linux/spinlock.h:334 [inline]
#1: 00000000cbb9b036 (&(&list->lock)->rlock#4){+...}, at:
tipc_link_reset+0xfa/0xdf0 net/tipc/link.c:849

stack backtrace:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.19.0-rc7+ #14
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1af/0x295 lib/dump_stack.c:113
print_deadlock_bug kernel/locking/lockdep.c:1759 [inline]
check_deadlock kernel/locking/lockdep.c:1803 [inline]
validate_chain kernel/locking/lockdep.c:2399 [inline]
__lock_acquire+0xf1e/0x3c60 kernel/locking/lockdep.c:3411
lock_acquire+0x1db/0x520 kernel/locking/lockdep.c:3900
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
_raw_spin_lock_bh+0x31/0x40 kernel/locking/spinlock.c:168
spin_lock_bh include/linux/spinlock.h:334 [inline]
tipc_link_reset+0x125/0xdf0 net/tipc/link.c:850
tipc_link_bc_create+0xb5/0x1f0 net/tipc/link.c:526
tipc_bcast_init+0x59b/0xab0 net/tipc/bcast.c:521
tipc_init_net+0x472/0x610 net/tipc/core.c:82
ops_init+0xf7/0x520 net/core/net_namespace.c:129
__register_pernet_operations net/core/net_namespace.c:940 [inline]
register_pernet_operations+0x453/0xac0 net/core/net_namespace.c:1011
register_pernet_subsys+0x28/0x40 net/core/net_namespace.c:1052
tipc_init+0x83/0x104 net/tipc/core.c:140
do_one_initcall+0x109/0x70a init/main.c:885
do_initcall_level init/main.c:953 [inline]
do_initcalls init/main.c:961 [inline]
do_basic_setup init/main.c:979 [inline]
kernel_init_freeable+0x4bd/0x57f init/main.c:1144
kernel_init+0x13/0x180 init/main.c:1063
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:413

The reason why the noise above was complained by LOCKDEP is because we
nested to hold l->wakeupq.lock and l->inputq->lock in tipc_link_reset
function. In fact it's unnecessary to move skb buffer from l->wakeupq
queue to l->inputq queue while holding the two locks at the same time.
Instead, we can move skb buffers in l->wakeupq queue to a temporary
list first and then move the buffers of the temporary list to l->inputq
queue, which is also safe for us.

Fixes: 3f32d0be6c16 ("tipc: lock wakeup & inputq at tipc_link_reset()")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Ying Xue <ying.xue@windriver.com>
---
net/tipc/link.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/tipc/link.c b/net/tipc/link.c
index fb886b5..1d21ae4 100644
--- a/net/tipc/link.c
+++ b/net/tipc/link.c
@@ -843,14 +843,21 @@ static void link_prepare_wakeup(struct tipc_link *l)

void tipc_link_reset(struct tipc_link *l)
{
+ struct sk_buff_head list;
+
+ __skb_queue_head_init(&list);
+
l->in_session = false;
l->session++;
l->mtu = l->advertised_mtu;
+
spin_lock_bh(&l->wakeupq.lock);
+ skb_queue_splice_init(&l->wakeupq, &list);
+ spin_unlock_bh(&l->wakeupq.lock);
+
spin_lock_bh(&l->inputq->lock);
- skb_queue_splice_init(&l->wakeupq, l->inputq);
+ skb_queue_splice_init(&list, l->inputq);
spin_unlock_bh(&l->inputq->lock);
- spin_unlock_bh(&l->wakeupq.lock);

__skb_queue_purge(&l->transmq);
__skb_queue_purge(&l->deferdq);
--
2.7.4
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