[PATCH net v2 0/2] kcm: don't sleep in softirq when the lower socket uses kTLS

[Rishikesh Jethwani <rjethwani@purestorage.com>]

When a TCP socket with software kTLS RX is attached to a KCM mux,
psock_data_ready() calls strp_data_ready() from softirq, which calls the
socket's read_sock(). For kTLS that is tls_sw_read_sock(), which can
sleep, and CONFIG_DEBUG_ATOMIC_SLEEP reports it on every run of a
loopback reproducer.

Patch 1 is the fix: KCM parses inline only when read_sock is
tcp_read_sock() and otherwise defers to the strparser work, which runs
under lock_sock(). It applies and builds on its own, including on
stable kernels.

Patch 2 addresses review feedback on v1 and is needed by patch 1.
kstrp, the workqueue that deferred work runs on, is an ordered
workqueue shared by every strparser user (KCM, sockmap, espintcp,
ovpn). With patch 1 alone, a KCM psock decrypting kTLS records in
software on kstrp would delay parsing and message timeouts for every
other strparser socket on the system. Patch 2 makes kstrp per-CPU. It
has no Fixes tag: the ordered workqueue is as old as strparser, and it
only becomes a real problem for KCM over kTLS with patch 1.

Other strparser users are not affected by the bug fixed in patch 1:
espintcp is itself a TCP ULP and cannot be combined with kTLS, ovpn
installs its own ops built from inet_stream_ops, and sockmap reads
through tcp_bpf_strp_read_sock() and is mutually exclusive with kTLS
RX (do_tls_setsockopt_conf() rejects sockets with a psock).

Testing: with patch 1, 5/5 runs of the reproducer produce no splat and
full datagram delivery; without it every run hits "BUG: sleeping
function called from invalid context" in strp_data_ready ->
tls_sw_read_sock. Multi-record messages (>16 KiB each) also deliver
completely with kTLS RX installed before the KCM attach and the whole
stream queued before the reader starts. With patch 2, test_sockmap and the ovpn TCP selftests
pass, strparser work runs concurrently across sockets, and dmesg shows
no warnings.

v2:
 - add patch 2 (kstrp per-CPU), per review
 - read sock->ops with READ_ONCE(), pairing with update_sk_prot()

v1: https://lore.kernel.org/netdev/20261013033920.2069285-1-rjethwani@purestorage.com/

Rishikesh Jethwani (2):
  kcm: defer receive parsing when the lower socket's read_sock may sleep
  strparser: don't serialize all parser work on one ordered workqueue

 net/kcm/kcmsock.c         | 33 +++++++++++++++++++++++++++++++--
 net/strparser/strparser.c |  2 +-
 2 files changed, 32 insertions(+), 3 deletions(-)

-- 
2.50.1