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rxrpc: peer->mtu_lock is redundant

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The peer->mtu_lock is only used to lock around writes to peer->max_data -
and nothing else; further, all such writes take place in the I/O thread and
the lock is only ever write-locked and never read-locked.

In a couple of places, the write_seqcount_begin() is wrapped in
preempt_disable/enable(), but not in all places.  This can cause lockdep to
complain:

WARNING: CPU: 0 PID: 1549 at include/linux/seqlock.h:221 rxrpc_input_ack_trailer+0x305/0x430
...
RIP: 0010:rxrpc_input_ack_trailer+0x305/0x430

Fix this by just getting rid of the lock.

Fixes: eeaedc5449d9 ("rxrpc: Implement path-MTU probing using padded PING ACKs (RFC8899)")
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/20250218192250.296870-3-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
David Howells 2025-02-18 19:22:45 +00:00 committed by Jakub Kicinski
parent c34d999ca3
commit 833fefa074
4 changed files with 1 additions and 12 deletions
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1
net/rxrpc/ar-internal.h
View File

@ -360,7 +360,6 @@ struct rxrpc_peer {
u8 pmtud_jumbo; /* Max jumbo packets for the MTU */
bool ackr_adv_pmtud; /* T if the peer advertises path-MTU */
unsigned int ackr_max_data; /* Maximum data advertised by peer */
seqcount_t mtu_lock; /* Lockless MTU access management */
unsigned int if_mtu; /* Local interface MTU (- hdrsize) for this peer */
unsigned int max_data; /* Maximum packet data capacity for this peer */
unsigned short hdrsize; /* header size (IP + UDP + RxRPC) */

2
net/rxrpc/input.c
View File

@ -810,9 +810,7 @@ static void rxrpc_input_ack_trailer(struct rxrpc_call *call, struct sk_buff *skb
if (max_mtu < peer->max_data) {
trace_rxrpc_pmtud_reduce(peer, sp->hdr.serial, max_mtu,
rxrpc_pmtud_reduce_ack);
write_seqcount_begin(&peer->mtu_lock);
peer->max_data = max_mtu;
write_seqcount_end(&peer->mtu_lock);
}
max_data = umin(max_mtu, peer->max_data);

9
net/rxrpc/peer_event.c
View File

@ -130,9 +130,7 @@ static void rxrpc_adjust_mtu(struct rxrpc_peer *peer, unsigned int mtu)
peer->pmtud_bad = max_data + 1;
trace_rxrpc_pmtud_reduce(peer, 0, max_data, rxrpc_pmtud_reduce_icmp);
write_seqcount_begin(&peer->mtu_lock);
peer->max_data = max_data;
write_seqcount_end(&peer->mtu_lock);
}
}
@ -408,13 +406,8 @@ void rxrpc_input_probe_for_pmtud(struct rxrpc_connection *conn, rxrpc_serial_t a
}
max_data = umin(max_data, peer->ackr_max_data);
if (max_data != peer->max_data) {
preempt_disable();
write_seqcount_begin(&peer->mtu_lock);
if (max_data != peer->max_data)
peer->max_data = max_data;
write_seqcount_end(&peer->mtu_lock);
preempt_enable();
}
jumbo = max_data + sizeof(struct rxrpc_jumbo_header);
jumbo /= RXRPC_JUMBO_SUBPKTLEN;

1
net/rxrpc/peer_object.c
View File

@ -235,7 +235,6 @@ struct rxrpc_peer *rxrpc_alloc_peer(struct rxrpc_local *local, gfp_t gfp,
peer->service_conns = RB_ROOT;
seqlock_init(&peer->service_conn_lock);
spin_lock_init(&peer->lock);
seqcount_init(&peer->mtu_lock);
peer->debug_id = atomic_inc_return(&rxrpc_debug_id);
peer->recent_srtt_us = UINT_MAX;
peer->cong_ssthresh = RXRPC_TX_MAX_WINDOW;