tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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ipv6: np->rxpmtu race annotation

Add READ_ONCE() annotations because np->rxpmtu can be changed
while udpv6_recvmsg() and rawv6_recvmsg() read it.

Since this is a very rarely used feature, and that udpv6_recvmsg()
and rawv6_recvmsg() read np->rxopt anyway, change the test order
so that np->rxpmtu does not need to be in a hot cache line.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20250916160951.541279-4-edumazet@google.com
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

authored by

Eric Dumazet and committed by
Paolo Abeni 9fba1eb3 5489f333

+2 -2
+1 -1
net/ipv6/raw.c
··· 445 445 if (flags & MSG_ERRQUEUE) 446 446 return ipv6_recv_error(sk, msg, len, addr_len); 447 447 448 - if (np->rxpmtu && np->rxopt.bits.rxpmtu) 448 + if (np->rxopt.bits.rxpmtu && READ_ONCE(np->rxpmtu)) 449 449 return ipv6_recv_rxpmtu(sk, msg, len, addr_len); 450 450 451 451 skb = skb_recv_datagram(sk, flags, &err);
+1 -1
net/ipv6/udp.c
··· 479 479 if (flags & MSG_ERRQUEUE) 480 480 return ipv6_recv_error(sk, msg, len, addr_len); 481 481 482 - if (np->rxpmtu && np->rxopt.bits.rxpmtu) 482 + if (np->rxopt.bits.rxpmtu && READ_ONCE(np->rxpmtu)) 483 483 return ipv6_recv_rxpmtu(sk, msg, len, addr_len); 484 484 485 485 try_again: