Merge branch 'hash-rethink'

Akhmat Karakotov says:

====================
Make hash rethink configurable

As it was shown in the report by Alexander Azimov, hash rethink at the
client-side may lead to connection timeout toward stateful anycast
services. Tom Herbert created a patchset to address this issue by applying
hash rethink only after a negative routing event (3RTOs) [1]. This change
also affects server-side behavior, which we found undesirable. This
patchset changes defaults in a way to make them safe: hash rethink at the
client-side is disabled and enabled at the server-side upon each RTO
event or in case of duplicate acknowledgments.

This patchset provides two options to change default behaviour. The hash
rethink may be disabled at the server-side by the new sysctl option.
Changes in the sysctl option don't affect default behavior at the
client-side.

Hash rethink can also be enabled/disabled with socket option or bpf
syscalls which ovewrite both default and sysctl settings. This socket
option is available on both client and server-side. This should provide
mechanics to enable hash rethink inside administrative domain, such as DC,
where hash rethink at the client-side can be desirable.

[1] https://lore.kernel.org/netdev/[email protected]/

v2:
	- Changed sysctl default to ENABLED in all patches. Reduced sysctl
	  and socket option size to u8. Fixed netns bug reported by kernel
	  test robot.

v3:
	- Fixed bug with bad u8 comparison. Moved sk_txrehash to use less
	  bytes in struct. Added WRITE_ONCE() in setsockopt in and
	  READ_ONCE() in tcp_rtx_synack.

v4:
	- Rebase and add documentation for sysctl option.

v5:
	- Move sk_txrehash out of busy poll ifdef.
====================

Signed-off-by: David S. Miller <[email protected]>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/uapi/linux/socket.h b/include/uapi/linux/socket.h
index eb0a9a5b6e71..51d6bb2f6765 100644
--- a/include/uapi/linux/socket.h
+++ b/include/uapi/linux/socket.h
@@ -31,4 +31,8 @@ struct __kernel_sockaddr_storage {
 
 #define SOCK_BUF_LOCK_MASK (SOCK_SNDBUF_LOCK | SOCK_RCVBUF_LOCK)
 
+#define SOCK_TXREHASH_DEFAULT	((u8)-1)
+#define SOCK_TXREHASH_DISABLED	0
+#define SOCK_TXREHASH_ENABLED	1
+
 #endif /* _UAPI_LINUX_SOCKET_H */