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Jakub Kicinski 026dfef287 tcp: give up on stronger sk_rcvbuf checks (for now) 
We hit another corner case which leads to TcpExtTCPRcvQDrop

Connections which send RPCs in the 20-80kB range over loopback
experience spurious drops. The exact conditions for most of
the drops I investigated are that:
 - socket exchanged >1MB of data so its not completely fresh
 - rcvbuf is around 128kB (default, hasn't grown)
 - there is ~60kB of data in rcvq
 - skb > 64kB arrives

The sum of skb->len (!) of both of the skbs (the one already
in rcvq and the arriving one) is larger than rwnd.
My suspicion is that this happens because __tcp_select_window()
rounds the rwnd up to (1 << wscale) if less than half of
the rwnd has been consumed.

Eric suggests that given the number of Fixes we already have
pointing to 1d2fbaad7c it's probably time to give up on it,
until a bigger revamp of rmem management.

Also while we could risk tweaking the rwnd math, there are other
drops on workloads I investigated, after the commit in question,
not explained by this phenomenon.

Suggested-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/20260225122355.585fd57b@kernel.org
Fixes: 1d2fbaad7c ("tcp: stronger sk_rcvbuf checks")
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260227003359.2391017-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2026-02-28 07:55:39 -08:00
..
6lowpan net: replace ND_PRINTK with dynamic debug 2025-07-10 15:27:32 -07:00
9p Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
802 Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
8021q Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
appletalk Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
atm Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
ax25 Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
batman-adv Here is a batman-adv bugfix: 2026-02-26 19:15:09 -08:00
bluetooth Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
bpf Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
bridge bridge: Check relevant per-VLAN options in VLAN range grouping 2026-02-26 19:24:29 -08:00
caif Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
can Convert more 'alloc_obj' cases to default GFP_KERNEL arguments 2026-02-21 20:03:00 -08:00
ceph Convert more 'alloc_obj' cases to default GFP_KERNEL arguments 2026-02-21 20:03:00 -08:00
core net: annotate data-races around sk->sk_{data_ready,write_space} 2026-02-26 19:23:03 -08:00
dcb Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
devlink Convert 'alloc_flex' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
dns_resolver net/dns_resolver: use credential guards in dns_query() 2025-11-04 12:36:51 +01:00
dsa Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
ethernet net: optimize eth_type_trans() vs CONFIG_STACKPROTECTOR_STRONG=y 2025-11-24 19:27:31 -08:00
ethtool Convert more 'alloc_obj' cases to default GFP_KERNEL arguments 2026-02-21 20:03:00 -08:00
handshake treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
hsr Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
ieee802154 Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
ife
ipv4 tcp: give up on stronger sk_rcvbuf checks (for now) 2026-02-28 07:55:39 -08:00
ipv6 inet: annotate data-races around isk->inet_num 2026-02-27 17:16:59 -08:00
iucv Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
kcm kcm: fix zero-frag skb in frag_list on partial sendmsg error 2026-02-23 17:26:55 -08:00
key Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
l2tp Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
l3mdev net: fib_rules: Fix iif / oif matching on L3 master device 2025-04-15 17:54:56 -07:00
lapb treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
llc treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
mac80211 Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
mac802154 Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
mctp Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
mpls Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
mptcp Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
ncsi Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
netfilter Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
netlabel Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
netlink Convert more 'alloc_obj' cases to default GFP_KERNEL arguments 2026-02-21 20:03:00 -08:00
netrom Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
nfc Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
nsh
openvswitch Convert more 'alloc_obj' cases to default GFP_KERNEL arguments 2026-02-21 20:03:00 -08:00
packet Convert more 'alloc_obj' cases to default GFP_KERNEL arguments 2026-02-21 20:03:00 -08:00
phonet treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
psample treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
psp Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
qrtr Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
rds Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
rfkill Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
rose Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
rxrpc Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
sched net/sched: Only allow act_ct to bind to clsact/ingress qdiscs and shared blocks 2026-02-27 19:06:21 -08:00
sctp Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
shaper Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
smc Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
strparser Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2025-11-13 12:35:38 -08:00
sunrpc Convert more 'alloc_obj' cases to default GFP_KERNEL arguments 2026-02-21 20:03:00 -08:00
switchdev treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
tipc Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
tls Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
unix net: annotate data-races around sk->sk_{data_ready,write_space} 2026-02-26 19:23:03 -08:00
vmw_vsock Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
wireless Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
x25 treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
xdp Convert remaining multi-line kmalloc_obj/flex GFP_KERNEL uses 2026-02-22 08:26:33 -08:00
xfrm Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
compat.c socket: Unify getsockname and getpeername implementation 2025-11-26 13:45:23 -07:00
devres.c
Kconfig net: Kconfig: discourage drop_monitor enablement 2025-10-17 16:29:26 -07:00
Kconfig.debug
Makefile psp: base PSP device support 2025-09-18 12:32:06 +02:00
socket.c net: Drop the lock in skb_may_tx_timestamp() 2026-02-24 11:27:29 +01:00
sysctl_net.c