rxrpc, afs: Fix peer hash locking vs RCU callback

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: 72904d7 ("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: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
Link: https://patch.msgid.link/2095618.1737622752@warthog.procyon.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: dhowells

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;

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);
 }