The rxrpc_assess_MTU_size() function calls down into the IP layer to find out the MTU size for a route. When accepting an incoming call, this is called from rxrpc_new_incoming_call() which holds interrupts disabled across the code that calls down to it. Unfortunately, the IP layer uses local_bh_enable() which, config dependent, throws a warning if IRQs are enabled:

WARNING: CPU: 1 PID: 5544 at kernel/softirq.c:387 __local_bh_enable_ip+0x43/0xd0 ... RIP: 0010:__local_bh_enable_ip+0x43/0xd0 ... Call Trace: <TASK> rt_cache_route+0x7e/0xa0 rt_set_nexthop.isra.0+0x3b3/0x3f0 __mkroute_output+0x43a/0x460 ip_route_output_key_hash+0xf7/0x140 ip_route_output_flow+0x1b/0x90 rxrpc_assess_MTU_size.isra.0+0x2a0/0x590 rxrpc_new_incoming_peer+0x46/0x120 rxrpc_alloc_incoming_call+0x1b1/0x400 rxrpc_new_incoming_call+0x1da/0x5e0 rxrpc_input_packet+0x827/0x900 rxrpc_io_thread+0x403/0xb60 kthread+0x2f7/0x310 ret_from_fork+0x2a/0x230 ret_from_fork_asm+0x1a/0x30 ... hardirqs last enabled at (23): _raw_spin_unlock_irq+0x24/0x50 hardirqs last disabled at (24): _raw_read_lock_irq+0x17/0x70 softirqs last enabled at (0): copy_process+0xc61/0x2730 softirqs last disabled at (25): rt_add_uncached_list+0x3c/0x90

Fix this by moving the call to rxrpc_assess_MTU_size() out of rxrpc_init_peer() and further up the stack where it can be done without interrupts disabled.

It shouldn't be a problem for rxrpc_new_incoming_call() to do it after the locks are dropped as pmtud is going to be performed by the I/O thread - and we're in the I/O thread at this point.

Fixes: a2ea9a907260 ("rxrpc: Use irq-disabling spinlocks between app and I/O thread") Signed-off-by: David Howells dhowells@redhat.com Reviewed-by: Jeffrey Altman jaltman@auristor.com cc: Marc Dionne marc.dionne@auristor.com cc: Junvyyang, Tencent Zhuque Lab zhuque@tencent.com cc: LePremierHomme kwqcheii@proton.me cc: Jakub Kicinski kuba@kernel.org cc: Paolo Abeni pabeni@redhat.com cc: "David S. Miller" davem@davemloft.net cc: Eric Dumazet edumazet@google.com cc: Simon Horman horms@kernel.org cc: linux-afs@lists.infradead.org cc: netdev@vger.kernel.org cc: stable@vger.kernel.org --- net/rxrpc/ar-internal.h | 1 + net/rxrpc/call_accept.c | 1 + net/rxrpc/peer_object.c | 6 ++---- 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h index 376e33dce8c1..df1a618dbf7d 100644 --- a/net/rxrpc/ar-internal.h +++ b/net/rxrpc/ar-internal.h @@ -1383,6 +1383,7 @@ struct rxrpc_peer *rxrpc_lookup_peer_rcu(struct rxrpc_local *, const struct sockaddr_rxrpc *); struct rxrpc_peer *rxrpc_lookup_peer(struct rxrpc_local *local, struct sockaddr_rxrpc *srx, gfp_t gfp); +void rxrpc_assess_MTU_size(struct rxrpc_local *local, struct rxrpc_peer *peer); struct rxrpc_peer *rxrpc_alloc_peer(struct rxrpc_local *, gfp_t, enum rxrpc_peer_trace); void rxrpc_new_incoming_peer(struct rxrpc_local *local, struct rxrpc_peer *peer); diff --git a/net/rxrpc/call_accept.c b/net/rxrpc/call_accept.c index 49fccee1a726..226b4bf82747 100644 --- a/net/rxrpc/call_accept.c +++ b/net/rxrpc/call_accept.c @@ -406,6 +406,7 @@ bool rxrpc_new_incoming_call(struct rxrpc_local *local,

spin_unlock(&rx->incoming_lock); read_unlock_irq(&local->services_lock); + rxrpc_assess_MTU_size(local, call->peer);

if (hlist_unhashed(&call->error_link)) { spin_lock_irq(&call->peer->lock); diff --git a/net/rxrpc/peer_object.c b/net/rxrpc/peer_object.c index e2f35e6c04d6..366431b0736c 100644 --- a/net/rxrpc/peer_object.c +++ b/net/rxrpc/peer_object.c @@ -149,8 +149,7 @@ struct rxrpc_peer *rxrpc_lookup_peer_rcu(struct rxrpc_local *local, * assess the MTU size for the network interface through which this peer is * reached */ -static void rxrpc_assess_MTU_size(struct rxrpc_local *local, - struct rxrpc_peer *peer) +void rxrpc_assess_MTU_size(struct rxrpc_local *local, struct rxrpc_peer *peer) { struct net *net = local->net; struct dst_entry *dst; @@ -277,8 +276,6 @@ static void rxrpc_init_peer(struct rxrpc_local *local, struct rxrpc_peer *peer,

peer->hdrsize += sizeof(struct rxrpc_wire_header); peer->max_data = peer->if_mtu - peer->hdrsize; - - rxrpc_assess_MTU_size(local, peer); }

/* @@ -297,6 +294,7 @@ static struct rxrpc_peer *rxrpc_create_peer(struct rxrpc_local *local, if (peer) { memcpy(&peer->srx, srx, sizeof(*srx)); rxrpc_init_peer(local, peer, hash_key); + rxrpc_assess_MTU_size(local, peer); }

_leave(" = %p", peer);