5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Eric Dumazet edumazet@google.com
[ Upstream commit 853c3bd7b7917670224c9fe5245bd045cac411dd ]
I noticed flakes in a packetdrill test, expecting an epoll_wait() to return EPOLLERR | EPOLLHUP on a failed connect() attempt, after multiple SYN retransmits. It sometimes return EPOLLERR only.
The issue is that tcp_write_err(): 1) writes an error in sk->sk_err, 2) calls sk_error_report(), 3) then calls tcp_done().
tcp_done() is writing SHUTDOWN_MASK into sk->sk_shutdown, among other things.
Problem is that the awaken user thread (from 2) sk_error_report()) might call tcp_poll() before tcp_done() has written sk->sk_shutdown.
tcp_poll() only sees a non zero sk->sk_err and returns EPOLLERR.
This patch fixes the issue by making sure to call sk_error_report() after tcp_done().
tcp_write_err() also lacks an smp_wmb().
We can reuse tcp_done_with_error() to factor out the details, as Neal suggested.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Eric Dumazet edumazet@google.com Acked-by: Neal Cardwell ncardwell@google.com Link: https://lore.kernel.org/r/20240528125253.1966136-3-edumazet@google.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/tcp_timer.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-)
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index ed01b775b8947..1a3a84992b9be 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -67,11 +67,7 @@ u32 tcp_clamp_probe0_to_user_timeout(const struct sock *sk, u32 when)
static void tcp_write_err(struct sock *sk) { - WRITE_ONCE(sk->sk_err, READ_ONCE(sk->sk_err_soft) ? : ETIMEDOUT); - sk_error_report(sk); - - tcp_write_queue_purge(sk); - tcp_done(sk); + tcp_done_with_error(sk, READ_ONCE(sk->sk_err_soft) ? : ETIMEDOUT); __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT); }