rxrpc, afs: Fix peer hash locking vs RCU callback

JIRA: https://issues.redhat.com/browse/RHEL-78388

commit 79d458c
Author: David Howells <dhowells@redhat.com>
Date:   Thu Jan 23 08:59:12 2025 +0000

    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>

Signed-off-by: Marc Dionne <mdionne@redhat.com>

Author: mdionne

net/rxrpc/peer_event.c

@@ -238,7 +238,7 @@ 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,
@@ -249,7 +249,7 @@ 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;
@@ -269,17 +269,17 @@ 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);
 }
 
 /*
@@ -309,7 +309,7 @@ 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);
@@ -321,7 +321,7 @@ 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

@@ -313,10 +313,10 @@ 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);
 }
 
 /*
@@ -348,7 +348,7 @@ 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);
@@ -361,7 +361,7 @@ 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);
@@ -411,10 +411,10 @@ 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);
 }