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tcp: fix mid stream window clamp.

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After the blamed commit below, if the user-space application performs
window clamping when tp->rcv_wnd is 0, the TCP socket will never be
able to announce a non 0 receive window, even after completely emptying
the receive buffer and re-setting the window clamp to higher values.

Refactor tcp_set_window_clamp() to address the issue: when the user
decreases the current clamp value, set rcv_ssthresh according to the
same logic used at buffer initialization, but ensuring reserved mem
provisioning.

To avoid code duplication factor-out the relevant bits from
tcp_adjust_rcv_ssthresh() in a new helper and reuse it in the above
scenario.

When increasing the clamp value, give the rcv_ssthresh a chance to grow
according to previously implemented heuristic.

Fixes: 3aa7857fe1 ("tcp: enable mid stream window clamp")
Reported-by: David Gibson <david@gibson.dropbear.id.au>
Reported-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/705dad54e6e6e9a010e571bf58e0b35a8ae70503.1701706073.git.pabeni@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Paolo Abeni 2023-12-04 17:08:05 +01:00 committed by Jakub Kicinski
parent d007caaaf0
commit 58d3aade20
2 changed files with 26 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
include/net/tcp.h
View File

@ -1514,17 +1514,22 @@ static inline int tcp_full_space(const struct sock *sk)
return tcp_win_from_space(sk, READ_ONCE(sk->sk_rcvbuf));
}
static inline void tcp_adjust_rcv_ssthresh(struct sock *sk)
static inline void __tcp_adjust_rcv_ssthresh(struct sock *sk, u32 new_ssthresh)
{
int unused_mem = sk_unused_reserved_mem(sk);
struct tcp_sock *tp = tcp_sk(sk);
tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
tp->rcv_ssthresh = min(tp->rcv_ssthresh, new_ssthresh);
if (unused_mem)
tp->rcv_ssthresh = max_t(u32, tp->rcv_ssthresh,
tcp_win_from_space(sk, unused_mem));
}
static inline void tcp_adjust_rcv_ssthresh(struct sock *sk)
{
__tcp_adjust_rcv_ssthresh(sk, 4U * tcp_sk(sk)->advmss);
}
void tcp_cleanup_rbuf(struct sock *sk, int copied);
void __tcp_cleanup_rbuf(struct sock *sk, int copied);

22
net/ipv4/tcp.c
View File

@ -3368,9 +3368,25 @@ int tcp_set_window_clamp(struct sock *sk, int val)
return -EINVAL;
tp->window_clamp = 0;
} else {
tp->window_clamp = val < SOCK_MIN_RCVBUF / 2 ?
SOCK_MIN_RCVBUF / 2 : val;
tp->rcv_ssthresh = min(tp->rcv_wnd, tp->window_clamp);
u32 new_rcv_ssthresh, old_window_clamp = tp->window_clamp;
u32 new_window_clamp = val < SOCK_MIN_RCVBUF / 2 ?
SOCK_MIN_RCVBUF / 2 : val;
if (new_window_clamp == old_window_clamp)
return 0;
tp->window_clamp = new_window_clamp;
if (new_window_clamp < old_window_clamp) {
/* need to apply the reserved mem provisioning only
* when shrinking the window clamp
*/
__tcp_adjust_rcv_ssthresh(sk, tp->window_clamp);
} else {
new_rcv_ssthresh = min(tp->rcv_wnd, tp->window_clamp);
tp->rcv_ssthresh = max(new_rcv_ssthresh,
tp->rcv_ssthresh);
}
}
return 0;
}