[PATCH v2 bpf-next 2/7] tools/memory-model: add BPF ringbuf MPSC litmus tests

[Andrii Nakryiko <andriin@fb.com>]

Add 4 litmus tests for BPF ringbuf implementation, divided into two different
use cases.

First, two unbounded case, one with 1 producer and another with
2 producers, single consumer. All reservations are supposed to succeed.

Second, bounded case with only 1 record allowed in ring buffer at any given
time. Here failures to reserve space are expected. Again, 1- and 2- producer
cases, single consumer, are validated.

Just for the fun of it, I also wrote a 3-producer cases, it took *16 hours* to
validate, but came back successful as well. I'm not including it in this
patch, because it's not practical to run it. See output for all included
4 cases and one 3-producer one with bounded use case.

Each litmust test implements producer/consumer protocol for BPF ring buffer
implementation found in kernel/bpf/ringbuf.c. Due to limitations, all records
are assumed equal-sized and producer/consumer counters are incremented by 1.
This doesn't change the correctness of the algorithm, though.

Verification results:
/* 1p1c bounded case */
$ herd7 -unroll 0 -conf linux-kernel.cfg litmus-tests/mpsc-rb+1p1c+bounded.litmus
Test mpsc-rb+1p1c+bounded Allowed
States 2
0:rFail=0; 1:rFail=0; cx=0; dropped=0; len1=1; px=1;
0:rFail=0; 1:rFail=0; cx=1; dropped=0; len1=1; px=1;
Ok
Witnesses
Positive: 3 Negative: 0
Condition exists (0:rFail=0 /\ 1:rFail=0 /\ dropped=0 /\ px=1 /\ len1=1 /\ (cx=0 \/ cx=1))
Observation mpsc-rb+1p1c+bounded Always 3 0
Time mpsc-rb+1p1c+bounded 0.03
Hash=5bdad0f41557a641370e7fa6b8eb2f43

/* 2p1c bounded case */
$ herd7 -unroll 0 -conf linux-kernel.cfg litmus-tests/mpsc-rb+2p1c+bounded.litmus
Test mpsc-rb+2p1c+bounded Allowed
States 4
0:rFail=0; 1:rFail=0; 2:rFail=0; cx=0; dropped=1; len1=1; px=1;
0:rFail=0; 1:rFail=0; 2:rFail=0; cx=1; dropped=0; len1=1; px=2;
0:rFail=0; 1:rFail=0; 2:rFail=0; cx=1; dropped=1; len1=1; px=1;
0:rFail=0; 1:rFail=0; 2:rFail=0; cx=2; dropped=0; len1=1; px=2;
Ok
Witnesses
Positive: 22 Negative: 0
Condition exists (0:rFail=0 /\ 1:rFail=0 /\ 2:rFail=0 /\ len1=1 /\ (dropped=0 /\ px=2 /\ (cx=1 \/ cx=2) \/ dropped=1 /\ px=1 /\ (cx=0 \/ cx=1)))
Observation mpsc-rb+2p1c+bounded Always 22 0
Time mpsc-rb+2p1c+bounded 119.38
Hash=e2f8f442a02bf7d8c2988ba82cf002d2

/* 1p1c unbounded case */
$ herd7 -unroll 0 -conf linux-kernel.cfg litmus-tests/mpsc-rb+1p1c+unbound.litmus
Test mpsc-rb+1p1c+unbound Allowed
States 2
0:rFail=0; 1:rFail=0; cx=0; len1=1; px=1;
0:rFail=0; 1:rFail=0; cx=1; len1=1; px=1;
Ok
Witnesses
Positive: 3 Negative: 0
Condition exists (0:rFail=0 /\ 1:rFail=0 /\ px=1 /\ len1=1 /\ (cx=0 \/ cx=1))
Observation mpsc-rb+1p1c+unbound Always 3 0
Time mpsc-rb+1p1c+unbound 0.02
Hash=be9de6487d8e27c3d37802d122e4a87c

/* 2p1c unbounded case */
$ herd7 -unroll 0 -conf linux-kernel.cfg litmus-tests/mpsc-rb+2p1c+unbound.litmus
Test mpsc-rb+2p1c+unbound Allowed
States 3
0:rFail=0; 1:rFail=0; 2:rFail=0; cx=0; len1=1; len2=1; px=2;
0:rFail=0; 1:rFail=0; 2:rFail=0; cx=1; len1=1; len2=1; px=2;
0:rFail=0; 1:rFail=0; 2:rFail=0; cx=2; len1=1; len2=1; px=2;
Ok
Witnesses
Positive: 42 Negative: 0
Condition exists (0:rFail=0 /\ 1:rFail=0 /\ 2:rFail=0 /\ px=2 /\ len1=1 /\ len2=1 /\ (cx=0 \/ cx=1 \/ cx=2))
Observation mpsc-rb+2p1c+unbound Always 42 0
Time mpsc-rb+2p1c+unbound 39.19
Hash=f0352aba9bdc03dd0b1def7d0c4956fa

/* 3p1c bounded case */
$ herd7 -unroll 0 -conf linux-kernel.cfg mpsc-rb+3p1c+bounded.litmus
Test mpsc+ringbuf-spinlock Allowed
States 5
0:rFail=0; 1:rFail=0; 2:rFail=0; 3:rFail=0; cx=0; len1=1; len2=1; px=2;
0:rFail=0; 1:rFail=0; 2:rFail=0; 3:rFail=0; cx=1; len1=1; len2=1; px=2;
0:rFail=0; 1:rFail=0; 2:rFail=0; 3:rFail=0; cx=1; len1=1; len2=1; px=3;
0:rFail=0; 1:rFail=0; 2:rFail=0; 3:rFail=0; cx=2; len1=1; len2=1; px=2;
0:rFail=0; 1:rFail=0; 2:rFail=0; 3:rFail=0; cx=2; len1=1; len2=1; px=3;
Ok
Witnesses
Positive: 558 Negative: 0
Condition exists (0:rFail=0 /\ 1:rFail=0 /\ 2:rFail=0 /\ 3:rFail=0 /\ len1=1 /\ len2=1 /\ (px=2 /\ (cx=0 \/ cx=1 \/ cx=2) \/ px=3 /\ (cx=1 \/ cx=2)))
Observation mpsc+ringbuf-spinlock Always 558 0
Time mpsc+ringbuf-spinlock 57487.24
Hash=133977dba930d167b4e1b4a6923d5687

Cc: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 .../litmus-tests/mpsc-rb+1p1c+bounded.litmus  |  92 +++++++++++
 .../litmus-tests/mpsc-rb+1p1c+unbound.litmus  |  83 ++++++++++
 .../litmus-tests/mpsc-rb+2p1c+bounded.litmus  | 152 ++++++++++++++++++
 .../litmus-tests/mpsc-rb+2p1c+unbound.litmus  | 137 ++++++++++++++++
 4 files changed, 464 insertions(+)
 create mode 100644 tools/memory-model/litmus-tests/mpsc-rb+1p1c+bounded.litmus
 create mode 100644 tools/memory-model/litmus-tests/mpsc-rb+1p1c+unbound.litmus
 create mode 100644 tools/memory-model/litmus-tests/mpsc-rb+2p1c+bounded.litmus
 create mode 100644 tools/memory-model/litmus-tests/mpsc-rb+2p1c+unbound.litmus

diff --git a/tools/memory-model/litmus-tests/mpsc-rb+1p1c+bounded.litmus b/tools/memory-model/litmus-tests/mpsc-rb+1p1c+bounded.litmus
new file mode 100644
index 000000000000..cafd17afe11e
--- /dev/null
+++ b/tools/memory-model/litmus-tests/mpsc-rb+1p1c+bounded.litmus
@@ -0,0 +1,92 @@
+C mpsc-rb+1p1c+bounded
+
+(*
+ * Result: Always
+ *
+ * This litmus test validates BPF ring buffer implementation under the
+ * following assumptions:
+ * - 1 producer;
+ * - 1 consumer;
+ * - ring buffer has capacity for only 1 record.
+ *
+ * Expectations:
+ * - 1 record pushed into ring buffer;
+ * - 0 or 1 element is consumed.
+ * - no failures.
+ *)
+
+{
+	max_len = 1;
+	len1 = 0;
+	px = 0;
+	cx = 0;
+	dropped = 0;
+}
+
+P0(int *len1, int *cx, int *px)
+{
+	int *rLenPtr;
+	int rLen;
+	int rPx;
+	int rCx;
+	int rFail;
+
+	rFail = 0;
+	rCx = smp_load_acquire(cx);
+
+	rPx = smp_load_acquire(px);
+	if (rCx < rPx) {
+		if (rCx == 0)
+			rLenPtr = len1;
+		else
+			rFail = 1;
+
+		rLen = smp_load_acquire(rLenPtr);
+		if (rLen == 0) {
+			rFail = 1;
+		} else if (rLen == 1) {
+			rCx = rCx + 1;
+			smp_store_release(cx, rCx);
+		}
+	}
+}
+
+P1(int *len1, spinlock_t *rb_lock, int *px, int *cx, int *dropped, int *max_len)
+{
+	int rPx;
+	int rCx;
+	int rFail;
+	int *rLenPtr;
+
+	rFail = 0;
+	rCx = smp_load_acquire(cx);
+
+	spin_lock(rb_lock);
+
+	rPx = *px;
+	if (rPx - rCx >= *max_len) {
+		atomic_inc(dropped);
+		spin_unlock(rb_lock);
+	} else {
+		if (rPx == 0)
+			rLenPtr = len1;
+		else
+			rFail = 1;
+
+		*rLenPtr = -1;
+		smp_wmb();
+		smp_store_release(px, rPx + 1);
+
+		spin_unlock(rb_lock);
+
+		smp_store_release(rLenPtr, 1);
+	}
+}
+
+exists (
+	0:rFail=0 /\ 1:rFail=0
+	/\
+	(
+		(dropped=0 /\ px=1 /\ len1=1 /\ (cx=0 \/ cx=1))
+	)
+)
diff --git a/tools/memory-model/litmus-tests/mpsc-rb+1p1c+unbound.litmus b/tools/memory-model/litmus-tests/mpsc-rb+1p1c+unbound.litmus
new file mode 100644
index 000000000000..84f660598015
--- /dev/null
+++ b/tools/memory-model/litmus-tests/mpsc-rb+1p1c+unbound.litmus
@@ -0,0 +1,83 @@
+C mpsc-rb+1p1c+unbound
+
+(*
+ * Result: Always
+ *
+ * This litmus test validates BPF ring buffer implementation under the
+ * following assumptions:
+ * - 1 producer;
+ * - 1 consumer;
+ * - ring buffer capacity is unbounded.
+ *
+ * Expectations:
+ * - 1 record pushed into ring buffer;
+ * - 0 or 1 element is consumed.
+ * - no failures.
+ *)
+
+{
+	len1 = 0;
+	px = 0;
+	cx = 0;
+}
+
+P0(int *len1, int *cx, int *px)
+{
+	int *rLenPtr;
+	int rLen;
+	int rPx;
+	int rCx;
+	int rFail;
+
+	rFail = 0;
+	rCx = smp_load_acquire(cx);
+
+	rPx = smp_load_acquire(px);
+	if (rCx < rPx) {
+		if (rCx == 0)
+			rLenPtr = len1;
+		else
+			rFail = 1;
+
+		rLen = smp_load_acquire(rLenPtr);
+		if (rLen == 0) {
+			rFail = 1;
+		} else if (rLen == 1) {
+			rCx = rCx + 1;
+			smp_store_release(cx, rCx);
+		}
+	}
+}
+
+P1(int *len1, spinlock_t *rb_lock, int *px, int *cx)
+{
+	int rPx;
+	int rCx;
+	int rFail;
+	int *rLenPtr;
+
+	rFail = 0;
+	rCx = smp_load_acquire(cx);
+
+	spin_lock(rb_lock);
+
+	rPx = *px;
+	if (rPx == 0)
+		rLenPtr = len1;
+	else
+		rFail = 1;
+
+	*rLenPtr = -1;
+	smp_wmb();
+	smp_store_release(px, rPx + 1);
+
+	spin_unlock(rb_lock);
+
+	smp_store_release(rLenPtr, 1);
+}
+
+exists (
+	0:rFail=0 /\ 1:rFail=0
+	/\ px=1 /\ len1=1
+	/\ (cx=0 \/ cx=1)
+)
diff --git a/tools/memory-model/litmus-tests/mpsc-rb+2p1c+bounded.litmus b/tools/memory-model/litmus-tests/mpsc-rb+2p1c+bounded.litmus
new file mode 100644
index 000000000000..900104c4933b
--- /dev/null
+++ b/tools/memory-model/litmus-tests/mpsc-rb+2p1c+bounded.litmus
@@ -0,0 +1,152 @@
+C mpsc-rb+2p1c+bounded
+
+(*
+ * Result: Always
+ *
+ * This litmus test validates BPF ring buffer implementation under the
+ * following assumptions:
+ * - 2 identical producers;
+ * - 1 consumer;
+ * - ring buffer has capacity for only 1 record.
+ *
+ * Expectations:
+ * - either 1 or 2 records are pushed into ring buffer;
+ * - 0, 1, or 2 elements are consumed by consumer;
+ * - appropriate number of dropped records is recorded to satisfy ring buffer
+ *   size bounds;
+ * - no failures.
+ *)
+
+{
+	max_len = 1;
+	len1 = 0;
+	px = 0;
+	cx = 0;
+	dropped = 0;
+}
+
+P0(int *len1, int *cx, int *px)
+{
+	int *rLenPtr;
+	int rLen;
+	int rPx;
+	int rCx;
+	int rFail;
+
+	rFail = 0;
+	rCx = smp_load_acquire(cx);
+
+	rPx = smp_load_acquire(px);
+	if (rCx < rPx) {
+		if (rCx == 0)
+			rLenPtr = len1;
+		else if (rCx == 1)
+			rLenPtr = len1;
+		else
+			rFail = 1;
+
+		rLen = smp_load_acquire(rLenPtr);
+		if (rLen == 0) {
+			rFail = 1;
+		} else if (rLen == 1) {
+			rCx = rCx + 1;
+			smp_store_release(cx, rCx);
+		}
+	}
+
+	rPx = smp_load_acquire(px);
+	if (rCx < rPx) {
+		if (rCx == 0)
+			rLenPtr = len1;
+		else if (rCx == 1)
+			rLenPtr = len1;
+		else
+			rFail = 1;
+
+		rLen = smp_load_acquire(rLenPtr);
+		if (rLen == 0) {
+			rFail = 1;
+		} else if (rLen == 1) {
+			rCx = rCx + 1;
+			smp_store_release(cx, rCx);
+		}
+	}
+}
+
+P1(int *len1, spinlock_t *rb_lock, int *px, int *cx, int *dropped, int *max_len)
+{
+	int rPx;
+	int rCx;
+	int rFail;
+	int *rLenPtr;
+
+	rFail = 0;
+	rCx = smp_load_acquire(cx);
+
+	spin_lock(rb_lock);
+
+	rPx = *px;
+	if (rPx - rCx >= *max_len) {
+		atomic_inc(dropped);
+		spin_unlock(rb_lock);
+	} else {
+		if (rPx == 0)
+			rLenPtr = len1;
+		else if (rPx == 1)
+			rLenPtr = len1;
+		else
+			rFail = 1;
+
+		*rLenPtr = -1;
+		smp_wmb();
+		smp_store_release(px, rPx + 1);
+
+		spin_unlock(rb_lock);
+
+		smp_store_release(rLenPtr, 1);
+	}
+}
+
+P2(int *len1, spinlock_t *rb_lock, int *px, int *cx, int *dropped, int *max_len)
+{
+	int rPx;
+	int rCx;
+	int rFail;
+	int *rLenPtr;
+
+	rFail = 0;
+	rCx = smp_load_acquire(cx);
+
+	spin_lock(rb_lock);
+
+	rPx = *px;
+	if (rPx - rCx >= *max_len) {
+		atomic_inc(dropped);
+		spin_unlock(rb_lock);
+	} else {
+		if (rPx == 0)
+			rLenPtr = len1;
+		else if (rPx == 1)
+			rLenPtr = len1;
+		else
+			rFail = 1;
+
+		*rLenPtr = -1;
+		smp_wmb();
+		smp_store_release(px, rPx + 1);
+
+		spin_unlock(rb_lock);
+
+		smp_store_release(rLenPtr, 1);
+	}
+}
+
+exists (
+	0:rFail=0 /\ 1:rFail=0 /\ 2:rFail=0 /\ len1=1
+	/\
+	(
+		(dropped = 0 /\ px=2 /\ (cx=1 \/ cx=2))
+		\/
+		(dropped = 1 /\ px=1 /\ (cx=0 \/ cx=1))
+	)
+)
diff --git a/tools/memory-model/litmus-tests/mpsc-rb+2p1c+unbound.litmus b/tools/memory-model/litmus-tests/mpsc-rb+2p1c+unbound.litmus
new file mode 100644
index 000000000000..83372e9eb079
--- /dev/null
+++ b/tools/memory-model/litmus-tests/mpsc-rb+2p1c+unbound.litmus
@@ -0,0 +1,137 @@
+C mpsc-rb+2p1c+unbound
+
+(*
+ * Result: Always
+ *
+ * This litmus test validates BPF ring buffer implementation under the
+ * following assumptions:
+ * - 2 identical producers;
+ * - 1 consumer;
+ * - ring buffer capacity is unbounded.
+ *
+ * Expectations:
+ * - 2 records pushed into ring buffer;
+ * - 0, 1, or 2 elements are consumed.
+ * - no failures.
+ *)
+
+{
+	len1 = 0;
+	len2 = 0;
+	px = 0;
+	cx = 0;
+}
+
+P0(int *len1, int *len2, int *cx, int *px)
+{
+	int *rLenPtr;
+	int rLen;
+	int rPx;
+	int rCx;
+	int rFail;
+
+	rFail = 0;
+	rCx = smp_load_acquire(cx);
+
+	rPx = smp_load_acquire(px);
+	if (rCx < rPx) {
+		if (rCx == 0)
+			rLenPtr = len1;
+		else if (rCx == 1)
+			rLenPtr = len2;
+		else
+			rFail = 1;
+
+		rLen = smp_load_acquire(rLenPtr);
+		if (rLen == 0) {
+			rFail = 1;
+		} else if (rLen == 1) {
+			rCx = rCx + 1;
+			smp_store_release(cx, rCx);
+		}
+	}
+
+	rPx = smp_load_acquire(px);
+	if (rCx < rPx) {
+		if (rCx == 0)
+			rLenPtr = len1;
+		else if (rCx == 1)
+			rLenPtr = len2;
+		else
+			rFail = 1;
+
+		rLen = smp_load_acquire(rLenPtr);
+		if (rLen == 0) {
+			rFail = 1;
+		} else if (rLen == 1) {
+			rCx = rCx + 1;
+			smp_store_release(cx, rCx);
+		}
+	}
+}
+
+P1(int *len1, int *len2, spinlock_t *rb_lock, int *px, int *cx)
+{
+	int rPx;
+	int rCx;
+	int rFail;
+	int *rLenPtr;
+
+	rFail = 0;
+	rCx = smp_load_acquire(cx);
+
+	spin_lock(rb_lock);
+
+	rPx = *px;
+	if (rPx == 0)
+		rLenPtr = len1;
+	else if (rPx == 1)
+		rLenPtr = len2;
+	else
+		rFail = 1;
+
+	*rLenPtr = -1;
+	smp_wmb();
+	smp_store_release(px, rPx + 1);
+
+	spin_unlock(rb_lock);
+
+	smp_store_release(rLenPtr, 1);
+}
+
+P2(int *len1, int *len2, spinlock_t *rb_lock, int *px, int *cx)
+{
+	int rPx;
+	int rCx;
+	int rFail;
+	int *rLenPtr;
+
+	rFail = 0;
+	rCx = smp_load_acquire(cx);
+
+	spin_lock(rb_lock);
+
+	rPx = *px;
+	if (rPx == 0)
+		rLenPtr = len1;
+	else if (rPx == 1)
+		rLenPtr = len2;
+	else
+		rFail = 1;
+
+	*rLenPtr = -1;
+	smp_wmb();
+	smp_store_release(px, rPx + 1);
+
+	spin_unlock(rb_lock);
+
+	smp_store_release(rLenPtr, 1);
+}
+
+exists (
+	0:rFail=0 /\ 1:rFail=0 /\ 2:rFail=0
+	/\
+	px=2 /\ len1=1 /\ len2=1
+	/\
+	(cx=0 \/ cx=1 \/ cx=2)
+)
-- 
2.24.1