[PATCH net] rxrpc, afs: Fix peer hash locking vs RCU callback

David Howells
2025-01-23T08:59:24Z

In its address list, afs now retains pointers to and refs on one or more
rxrpc_peer objects. The address list is freed under RCU and at this time,
it puts the refs on those peers.

Now, when an rxrpc_peer object runs out of refs, it gets removed from the
peer hash table and, for that, rxrpc has to take a spinlock. However, it
is now being called from afs's RCU cleanup, which takes place in BH
context - but it is just taking an ordinary spinlock.

The put may also be called from non-BH context, and so there exists the
possibility of deadlock if the BH-based RCU cleanup happens whilst the hash
spinlock is held. This led to the attached lockdep complaint.

Fix this by changing spinlocks of rxnet->peer_hash_lock back to
BH-disabling locks.

================================
WARNING: inconsistent lock state
6.13.0-rc5-build2+ #1223 Tainted: G E
--------------------------------
inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
swapper/1/0 [HC0[0]:SC1[1]:HE1:SE0] takes:
ffff88810babe228 (&rxnet->peer_hash_lock){+.?.}-{3:3}, at: rxrpc_put_peer+0xcb/0x180
{SOFTIRQ-ON-W} state was registered at:
mark_usage+0x164/0x180
__lock_acquire+0x544/0x990
lock_acquire.part.0+0x103/0x280
_raw_spin_lock+0x2f/0x40
rxrpc_peer_keepalive_worker+0x144/0x440
process_one_work+0x486/0x7c0
process_scheduled_works+0x73/0x90
worker_thread+0x1c8/0x2a0
kthread+0x19b/0x1b0
ret_from_fork+0x24/0x40
ret_from_fork_asm+0x1a/0x30
irq event stamp: 972402
hardirqs last enabled at (972402): [<ffffffff8244360e>] _raw_spin_unlock_irqrestore+0x2e/0x50
hardirqs last disabled at (972401): [<ffffffff82443328>] _raw_spin_lock_irqsave+0x18/0x60
softirqs last enabled at (972300): [<ffffffff810ffbbe>] handle_softirqs+0x3ee/0x430
softirqs last disabled at (972313): [<ffffffff810ffc54>] __irq_exit_rcu+0x44/0x110

other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&rxnet->peer_hash_lock);
<Interrupt>
lock(&rxnet->peer_hash_lock);

*** DEADLOCK ***
1 lock held by swapper/1/0:
#0: ffffffff83576be0 (rcu_callback){....}-{0:0}, at: rcu_lock_acquire+0x7/0x30

stack backtrace:
CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Tainted: G E 6.13.0-rc5-build2+ #1223
Tainted: [E]=UNSIGNED_MODULE
Hardware name: ASUS All Series/H97-PLUS, BIOS 2306 10/09/2014
Call Trace:
<IRQ>
dump_stack_lvl+0x57/0x80
print_usage_bug.part.0+0x227/0x240
valid_state+0x53/0x70
mark_lock_irq+0xa5/0x2f0
mark_lock+0xf7/0x170
mark_usage+0xe1/0x180
__lock_acquire+0x544/0x990
lock_acquire.part.0+0x103/0x280
_raw_spin_lock+0x2f/0x40
rxrpc_put_peer+0xcb/0x180
afs_free_addrlist+0x46/0x90 [kafs]
rcu_do_batch+0x2d2/0x640
rcu_core+0x2f7/0x350
handle_softirqs+0x1ee/0x430
__irq_exit_rcu+0x44/0x110
irq_exit_rcu+0xa/0x30
sysvec_apic_timer_interrupt+0x7f/0xa0
</IRQ>

Fixes: 72904d7b9bfb ("rxrpc, afs: Allow afs to pin rxrpc_peer objects")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: netdev@vger.kernel.org
---
net/rxrpc/peer_event.c | 16 ++++++++--------
net/rxrpc/peer_object.c | 12 ++++++------
2 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/net/rxrpc/peer_event.c b/net/rxrpc/peer_event.c
index d82e44a3901b..e874c31fa901 100644
--- a/net/rxrpc/peer_event.c
+++ b/net/rxrpc/peer_event.c
@@ -246,7 +246,7 @@ static void rxrpc_peer_keepalive_dispatch(struct rxrpc_net *rxnet,
bool use;
int slot;

- spin_lock(&rxnet->peer_hash_lock);
+ spin_lock_bh(&rxnet->peer_hash_lock);

while (!list_empty(collector)) {
peer = list_entry(collector->next,
@@ -257,7 +257,7 @@ static void rxrpc_peer_keepalive_dispatch(struct rxrpc_net *rxnet,
continue;

use = __rxrpc_use_local(peer->local, rxrpc_local_use_peer_keepalive);
- spin_unlock(&rxnet->peer_hash_lock);
+ spin_unlock_bh(&rxnet->peer_hash_lock);

if (use) {
keepalive_at = peer->last_tx_at + RXRPC_KEEPALIVE_TIME;
@@ -277,17 +277,17 @@ static void rxrpc_peer_keepalive_dispatch(struct rxrpc_net *rxnet,
*/
slot += cursor;
slot &= mask;
- spin_lock(&rxnet->peer_hash_lock);
+ spin_lock_bh(&rxnet->peer_hash_lock);
list_add_tail(&peer->keepalive_link,
&rxnet->peer_keepalive[slot & mask]);
- spin_unlock(&rxnet->peer_hash_lock);
+ spin_unlock_bh(&rxnet->peer_hash_lock);
rxrpc_unuse_local(peer->local, rxrpc_local_unuse_peer_keepalive);
}
rxrpc_put_peer(peer, rxrpc_peer_put_keepalive);
- spin_lock(&rxnet->peer_hash_lock);
+ spin_lock_bh(&rxnet->peer_hash_lock);
}

- spin_unlock(&rxnet->peer_hash_lock);
+ spin_unlock_bh(&rxnet->peer_hash_lock);
}

/*
@@ -317,7 +317,7 @@ void rxrpc_peer_keepalive_worker(struct work_struct *work)
* second; the bucket at cursor + 1 goes at now + 1s and so
* on...
*/
- spin_lock(&rxnet->peer_hash_lock);
+ spin_lock_bh(&rxnet->peer_hash_lock);
list_splice_init(&rxnet->peer_keepalive_new, &collector);

stop = cursor + ARRAY_SIZE(rxnet->peer_keepalive);
@@ -329,7 +329,7 @@ void rxrpc_peer_keepalive_worker(struct work_struct *work)
}

base = now;
- spin_unlock(&rxnet->peer_hash_lock);
+ spin_unlock_bh(&rxnet->peer_hash_lock);

rxnet->peer_keepalive_base = base;
rxnet->peer_keepalive_cursor = cursor;
diff --git a/net/rxrpc/peer_object.c b/net/rxrpc/peer_object.c
index e1c63129586b..0fcc87f0409f 100644
--- a/net/rxrpc/peer_object.c
+++ b/net/rxrpc/peer_object.c
@@ -325,10 +325,10 @@ void rxrpc_new_incoming_peer(struct rxrpc_local *local, struct rxrpc_peer *peer)
hash_key = rxrpc_peer_hash_key(local, &peer->srx);
rxrpc_init_peer(local, peer, hash_key);

- spin_lock(&rxnet->peer_hash_lock);
+ spin_lock_bh(&rxnet->peer_hash_lock);
hash_add_rcu(rxnet->peer_hash, &peer->hash_link, hash_key);
list_add_tail(&peer->keepalive_link, &rxnet->peer_keepalive_new);
- spin_unlock(&rxnet->peer_hash_lock);
+ spin_unlock_bh(&rxnet->peer_hash_lock);
}

/*
@@ -360,7 +360,7 @@ struct rxrpc_peer *rxrpc_lookup_peer(struct rxrpc_local *local,
return NULL;
}

- spin_lock(&rxnet->peer_hash_lock);
+ spin_lock_bh(&rxnet->peer_hash_lock);

/* Need to check that we aren't racing with someone else */
peer = __rxrpc_lookup_peer_rcu(local, srx, hash_key);
@@ -373,7 +373,7 @@ struct rxrpc_peer *rxrpc_lookup_peer(struct rxrpc_local *local,
&rxnet->peer_keepalive_new);
}

- spin_unlock(&rxnet->peer_hash_lock);
+ spin_unlock_bh(&rxnet->peer_hash_lock);

if (peer)
rxrpc_free_peer(candidate);
@@ -423,10 +423,10 @@ static void __rxrpc_put_peer(struct rxrpc_peer *peer)

ASSERT(hlist_empty(&peer->error_targets));

- spin_lock(&rxnet->peer_hash_lock);
+ spin_lock_bh(&rxnet->peer_hash_lock);
hash_del_rcu(&peer->hash_link);
list_del_init(&peer->keepalive_link);
- spin_unlock(&rxnet->peer_hash_lock);
+ spin_unlock_bh(&rxnet->peer_hash_lock);

rxrpc_free_peer(peer);
}