Add a packetdrill test that drives sk->sk_forward_alloc negative via tcp_collapse() on the receive queue while sk->sk_wmem_queued exceeds sysctl_tcp_wmem[0], and verifies that a subsequent non-blocking write() under TCP memory pressure fails with EAGAIN rather than returning a negative copy length from tcp_wmem_schedule() and failing with EFAULT.
Assisted-by: LLM Signed-off-by: Octavian Purdila <[email protected]> --- .../testing/selftests/net/packetdrill/config | 1 + .../tcp_wmem_schedule_negative_fwd_alloc.pkt | 116 ++++++++++++++++++ 2 files changed, 117 insertions(+) create mode 100644 tools/testing/selftests/net/packetdrill/tcp_wmem_schedule_negative_fwd_alloc.pkt diff --git a/tools/testing/selftests/net/packetdrill/config b/tools/testing/selftests/net/packetdrill/config index b7df8bf309200..dc3cd72a8da8c 100644 --- a/tools/testing/selftests/net/packetdrill/config +++ b/tools/testing/selftests/net/packetdrill/config @@ -1,6 +1,7 @@ CONFIG_HZ=1000 CONFIG_HZ_1000=y CONFIG_IPV6=y +CONFIG_MEMCG=y CONFIG_NET_NS=y CONFIG_NET_SCH_FIFO=y CONFIG_NET_SCH_FQ=y diff --git a/tools/testing/selftests/net/packetdrill/tcp_wmem_schedule_negative_fwd_alloc.pkt b/tools/testing/selftests/net/packetdrill/tcp_wmem_schedule_negative_fwd_alloc.pkt new file mode 100644 index 0000000000000..db232b54c554e --- /dev/null +++ b/tools/testing/selftests/net/packetdrill/tcp_wmem_schedule_negative_fwd_alloc.pkt @@ -0,0 +1,116 @@ +// SPDX-License-Identifier: GPL-2.0 +// Test that tcp_wmem_schedule() clamps negative sk->sk_forward_alloc to 0 +// when sk_wmem_schedule() fails under memory pressure and +// sk->sk_wmem_queued >= sysctl_tcp_wmem[0], returning EAGAIN rather than EFAULT. + +--mtu=65535 +--tolerance_usecs=100000 + +`set -e +./defaults.sh +ip link set dev tun0 mtu 65535 +sysctl -q net.ipv4.tcp_rmem="4096 131072 6291456" +sysctl -q net.ipv4.tcp_wmem="4096 16384 4194304" +cgroot=$(mount -t cgroup2 | head -1 | awk '{print $3}') +[ -n "$cgroot" ] +echo +memory > "${cgroot}/cgroup.subtree_control" +mkdir -p "${cgroot}/pkt_${PPID}" +echo $PPID > "${cgroot}/pkt_${PPID}/cgroup.procs" +` + +// Create listening socket in pkt_${PPID} memcg and establish connection +0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 ++0.000 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 ++0.000 bind(3, ..., ...) = 0 ++0.000 listen(3, 1) = 0 + ++0.000 < S 0:0(0) win 65535 <mss 36000,nop,wscale 7> ++0.000 > S. 0:0(0) ack 1 <...> ++0.000 < . 1:1(0) ack 1 win 512 ++0.000 accept(3, ..., ...) = 4 + +// Move packetdrill back to its original cgroup so only the sockets remain charged to pkt_${PPID} ++0.000 `cgroot=$(mount -t cgroup2 | head -1 | awk '{print $3}') +runner_pid=$(awk '/^PPid:/ {print $2}' /proc/$PPID/status) +orig_cg=$(sed -n 's/^0:://p' /proc/$runner_pid/cgroup) +echo $PPID > "${cgroot}${orig_cg}/cgroup.procs"` + ++0.000 setsockopt(4, SOL_SOCKET, SO_SNDBUF, [2097152], 4) = 0 ++0.000 setsockopt(4, SOL_SOCKET, SO_RCVBUF, [145536], 4) = 0 + +// 1. Warm up rcv_ssthresh to full window (~256 KB) ++0.000 < P. 1:36001(36000) ack 1 win 512 ++0.000 > . 1:1(0) ack 36001 ++0.000 read(4, ..., 36000) = 36000 + ++0.000 < P. 36001:72001(36000) ack 1 win 512 ++0.000 > . 1:1(0) ack 72001 ++0.000 read(4, ..., 36000) = 36000 + ++0.000 < P. 72001:108001(36000) ack 1 win 512 ++0.000 > . 1:1(0) ack 108001 ++0.000 read(4, ..., 36000) = 36000 + ++0.000 < P. 108001:144001(36000) ack 1 win 512 ++0.000 > . 1:1(0) ack 144001 ++0.000 read(4, ..., 36000) = 36000 + +// 2. Queue 500 KB on TX so sk_wmem_queued >= sysctl_tcp_wmem[0] ++0.000 write(4, ..., 500000) = 500000 + +// 3a. Inject 6 high-density 36 KB segments (216 KB payload, 222.7 KB truesize) +// and read 100 bytes from the head SKB so before(skb->seq, tp->copied_seq) is true. ++0.000 < P. 144001:180001(36000) ack 1 win 512 ++0.000 read(4, ..., 100) = 100 + ++0.000 < P. 180001:216001(36000) ack 1 win 512 ++0.000 < P. 216001:252001(36000) ack 1 win 512 ++0.000 < P. 252001:288001(36000) ack 1 win 512 ++0.000 < P. 288001:324001(36000) ack 1 win 512 ++0.000 < P. 324001:360001(36000) ack 1 win 512 + +// 3b. Inject 22 smaller 1000-byte segments into the remaining advertised rcv_wnd. +// Their higher truesize pushes sk_rmem_alloc > sk_rcvbuf (291072), +// triggering tcp_prune_queue -> tcp_collapse on the 216 KB of 36 KB SKBs +// and driving sk->sk_forward_alloc negative (-32768). ++0.000 < P. 360001:361001(1000) ack 1 win 512 ++0.000 < P. 361001:362001(1000) ack 1 win 512 ++0.000 < P. 362001:363001(1000) ack 1 win 512 ++0.000 < P. 363001:364001(1000) ack 1 win 512 ++0.000 < P. 364001:365001(1000) ack 1 win 512 ++0.000 < P. 365001:366001(1000) ack 1 win 512 ++0.000 < P. 366001:367001(1000) ack 1 win 512 ++0.000 < P. 367001:368001(1000) ack 1 win 512 ++0.000 < P. 368001:369001(1000) ack 1 win 512 ++0.000 < P. 369001:370001(1000) ack 1 win 512 ++0.000 < P. 370001:371001(1000) ack 1 win 512 ++0.000 < P. 371001:372001(1000) ack 1 win 512 ++0.000 < P. 372001:373001(1000) ack 1 win 512 ++0.000 < P. 373001:374001(1000) ack 1 win 512 ++0.000 < P. 374001:375001(1000) ack 1 win 512 ++0.000 < P. 375001:376001(1000) ack 1 win 512 ++0.000 < P. 376001:377001(1000) ack 1 win 512 ++0.000 < P. 377001:378001(1000) ack 1 win 512 ++0.000 < P. 378001:379001(1000) ack 1 win 512 ++0.000 < P. 379001:380001(1000) ack 1 win 512 ++0.000 < P. 380001:381001(1000) ack 1 win 512 ++0.000 < P. 381001:382001(1000) ack 1 win 512 + +// 4. Cap the socket memcg at its current usage and expect -EAGAIN on non-blocking write. ++0.010 `cgroot=$(mount -t cgroup2 | head -1 | awk '{print $3}') +echo 0 > "${cgroot}/pkt_${PPID}/memory.high" +cat "${cgroot}/pkt_${PPID}/memory.current" > "${cgroot}/pkt_${PPID}/memory.max"` ++0.000 fcntl(4, F_SETFL, O_RDWR|O_NONBLOCK) = 0 ++0.000 write(4, ..., 16384) = -1 EAGAIN (Resource temporarily unavailable) + ++0.000 close(4) = 0 ++0.000 close(3) = 0 + +// Untimed cleanup command executed by packetdrill on both pass and early failure. +`cgroot=$(mount -t cgroup2 | head -1 | awk '{print $3}') +[ -n "$cgroot" ] || exit 0 +runner_pid=$(awk '/^PPid:/ {print $2}' /proc/$PPID/status) +orig_cg=$(sed -n 's/^0:://p' /proc/$runner_pid/cgroup) +echo $PPID > "${cgroot}${orig_cg}/cgroup.procs" 2>/dev/null || true +echo $$ > "${cgroot}${orig_cg}/cgroup.procs" 2>/dev/null || true +rmdir "${cgroot}/pkt_${PPID}"` -- 2.56.0.176.g3575e65682-goog
