Add tests that verify that overflow conditions behave appropriately.
Specifically:
* if overflow is continually flushed, then CQEs should arrive mostly in
order to prevent starvation of some completions
* if CQEs are dropped due to GFP_ATOMIC allocation failures it is
possible to terminate cleanly. This is not tested by default as it
requires debug kernel config, and also has system-wide effects
Signed-off-by: Dylan Yudaken <dylany@xxxxxx>
---
test/cq-overflow.c | 248 +++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 241 insertions(+), 7 deletions(-)
diff --git a/test/cq-overflow.c b/test/cq-overflow.c
index 312b414b2a79..4265d48ae8af 100644
--- a/test/cq-overflow.c
+++ b/test/cq-overflow.c
@@ -9,6 +9,7 @@
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
+#include <assert.h>
#include "helpers.h"
#include "liburing.h"
@@ -21,6 +22,32 @@ static struct iovec *vecs;
#define ENTRIES 8
+/*
+ * io_uring has rare cases where CQEs are lost.
+ * This happens when there is no space in the CQ ring, and also there is no
+ * GFP_ATOMIC memory available. In reality this probably means that the process
+ * is about to be killed as many other things might start failing, but we still
+ * want to test that liburing and the kernel deal with this properly. The fault
+ * injection framework allows us to test this scenario. Unfortunately this
+ * requires some system wide changes and so we do not enable this by default.
+ * The tests in this file should work in both cases (where overflows are queued
+ * and where they are dropped) on recent kernels.
+ *
+ * In order to test dropped CQEs you should enable fault injection in the kernel
+ * config:
+ *
+ * CONFIG_FAULT_INJECTION=y
+ * CONFIG_FAILSLAB=y
+ * CONFIG_FAULT_INJECTION_DEBUG_FS=y
+ *
+ * and then run the test as follows:
+ * echo Y > /sys/kernel/debug/failslab/task-filter
+ * echo 100 > /sys/kernel/debug/failslab/probability
+ * echo 0 > /sys/kernel/debug/failslab/verbose
+ * echo 100000 > /sys/kernel/debug/failslab/times
+ * bash -c "echo 1 > /proc/self/make-it-fail && exec ./cq-overflow.t"
+ */
+
static int test_io(const char *file, unsigned long usecs, unsigned *drops, int fault)
{
struct io_uring_sqe *sqe;
@@ -29,6 +56,7 @@ static int test_io(const char *file, unsigned long usecs, unsigned *drops, int f
unsigned reaped, total;
struct io_uring ring;
int nodrop, i, fd, ret;
+ bool cqe_dropped = false;
fd = open(file, O_RDONLY | O_DIRECT);
if (fd < 0) {
@@ -104,8 +132,8 @@ static int test_io(const char *file, unsigned long usecs, unsigned *drops, int f
reap_it:
reaped = 0;
do {
- if (nodrop) {
- /* nodrop should never lose events */
+ if (nodrop && !cqe_dropped) {
+ /* nodrop should never lose events unless cqe_dropped */
if (reaped == total)
break;
} else {
@@ -113,7 +141,10 @@ reap_it:
break;
}
ret = io_uring_wait_cqe(&ring, &cqe);
- if (ret) {
+ if (nodrop && ret == -EBADR) {
+ cqe_dropped = true;
+ continue;
+ } else if (ret) {
fprintf(stderr, "wait_cqe=%d\n", ret);
goto err;
}
@@ -133,7 +164,7 @@ reap_it:
goto err;
}
- if (!nodrop) {
+ if (!nodrop || cqe_dropped) {
*drops = *ring.cq.koverflow;
} else if (*ring.cq.koverflow) {
fprintf(stderr, "Found %u overflows\n", *ring.cq.koverflow);
@@ -154,18 +185,29 @@ static int reap_events(struct io_uring *ring, unsigned nr_events, int do_wait)
{
struct io_uring_cqe *cqe;
int i, ret = 0, seq = 0;
+ unsigned int start_overflow = *ring->cq.koverflow;
+ bool dropped = false;
for (i = 0; i < nr_events; i++) {
if (do_wait)
ret = io_uring_wait_cqe(ring, &cqe);
else
ret = io_uring_peek_cqe(ring, &cqe);
- if (ret) {
+ if (do_wait && ret == -EBADR) {
+ unsigned int this_drop = *ring->cq.koverflow -
+ start_overflow;
+
+ dropped = true;
+ start_overflow = *ring->cq.koverflow;
+ assert(this_drop > 0);
+ i += (this_drop - 1);
+ continue;
+ } else if (ret) {
if (ret != -EAGAIN)
fprintf(stderr, "cqe peek failed: %d\n", ret);
break;
}
- if (cqe->user_data != seq) {
+ if (!dropped && cqe->user_data != seq) {
fprintf(stderr, "cqe sequence out-of-order\n");
fprintf(stderr, "got %d, wanted %d\n", (int) cqe->user_data,
seq);
@@ -242,19 +284,211 @@ err:
return 1;
}
+
+static void submit_one_nop(struct io_uring *ring, int ud)
+{
+ struct io_uring_sqe *sqe;
+ int ret;
+
+ sqe = io_uring_get_sqe(ring);
+ assert(sqe);
+ io_uring_prep_nop(sqe);
+ sqe->user_data = ud;
+ ret = io_uring_submit(ring);
+ assert(ret == 1);
+}
+
+/*
+ * Create an overflow condition and ensure that SQEs are still processed
+ */
+static int test_overflow_handling(
+ bool batch,
+ int cqe_multiple,
+ bool poll,
+ bool defer)
+{
+ struct io_uring ring;
+ struct io_uring_params p;
+ int ret, i, j, ud, cqe_count;
+ unsigned int count;
+ int const N = 8;
+ int const LOOPS = 128;
+ int const QUEUE_LENGTH = 1024;
+ int completions[N];
+ int queue[QUEUE_LENGTH];
+ int queued = 0;
+ int outstanding = 0;
+ bool cqe_dropped = false;
+
+ memset(&completions, 0, sizeof(int) * N);
+ memset(&p, 0, sizeof(p));
+ p.cq_entries = 2 * cqe_multiple;
+ p.flags |= IORING_SETUP_CQSIZE;
+
+ if (poll)
+ p.flags |= IORING_SETUP_IOPOLL;
+
+ if (defer)
+ p.flags |= IORING_SETUP_DEFER_TASKRUN;
+
+ ret = io_uring_queue_init_params(2, &ring, &p);
+ if (ret) {
+ fprintf(stderr, "io_uring_queue_init failed %d\n", ret);
+ return 1;
+ }
+
+ assert(p.cq_entries < N);
+ /* submit N SQEs, some should overflow */
+ for (i = 0; i < N; i++) {
+ submit_one_nop(&ring, i);
+ outstanding++;
+ }
+
+ for (i = 0; i < LOOPS; i++) {
+ struct io_uring_cqe *cqes[N];
+
+ if (io_uring_cq_has_overflow(&ring)) {
+ /*
+ * Flush any overflowed CQEs and process those. Actively
+ * flush these to make sure CQEs arrive in vague order
+ * of being sent.
+ */
+ ret = io_uring_get_events(&ring);
+ if (ret != 0) {
+ fprintf(stderr,
+ "io_uring_get_events returned %d\n",
+ ret);
+ goto err;
+ }
+ } else if (!cqe_dropped) {
+ for (j = 0; j < queued; j++) {
+ submit_one_nop(&ring, queue[j]);
+ outstanding++;
+ }
+ queued = 0;
+ }
+
+ /* We have lost some random cqes, stop if no remaining. */
+ if (cqe_dropped && outstanding == *ring.cq.koverflow)
+ break;
+
+ ret = io_uring_wait_cqe(&ring, &cqes[0]);
+ if (ret == -EBADR) {
+ cqe_dropped = true;
+ fprintf(stderr, "CQE dropped\n");
+ continue;
+ } else if (ret != 0) {
+ fprintf(stderr, "io_uring_wait_cqes failed %d\n", ret);
+ goto err;
+ }
+ cqe_count = 1;
+ if (batch) {
+ ret = io_uring_peek_batch_cqe(&ring, &cqes[0], 2);
+ if (ret < 0) {
+ fprintf(stderr,
+ "io_uring_peek_batch_cqe failed %d\n",
+ ret);
+ goto err;
+ }
+ cqe_count = ret;
+ }
+ for (j = 0; j < cqe_count; j++) {
+ assert(cqes[j]->user_data < N);
+ ud = cqes[j]->user_data;
+ completions[ud]++;
+ assert(queued < QUEUE_LENGTH);
+ queue[queued++] = (int)ud;
+ }
+ io_uring_cq_advance(&ring, cqe_count);
+ outstanding -= cqe_count;
+ }
+
+ /* See if there were any drops by flushing the CQ ring *and* overflow */
+ do {
+ struct io_uring_cqe *cqe;
+
+ ret = io_uring_get_events(&ring);
+ if (ret < 0) {
+ if (ret == -EBADR) {
+ fprintf(stderr, "CQE dropped\n");
+ cqe_dropped = true;
+ break;
+ }
+ goto err;
+ }
+ if (outstanding && !io_uring_cq_ready(&ring))
+ ret = io_uring_wait_cqe_timeout(&ring, &cqe, NULL);
+
+ if (ret && ret != -ETIME) {
+ if (ret == -EBADR) {
+ fprintf(stderr, "CQE dropped\n");
+ cqe_dropped = true;
+ break;
+ }
+ fprintf(stderr, "wait_cqe_timeout = %d\n", ret);
+ goto err;
+ }
+ count = io_uring_cq_ready(&ring);
+ io_uring_cq_advance(&ring, count);
+ outstanding -= count;
+ } while (count);
+
+ io_uring_queue_exit(&ring);
+
+ /* Make sure that completions come back in the same order they were
+ * sent. If they come back unfairly then this will concentrate on a
+ * couple of indices.
+ */
+ for (i = 1; !cqe_dropped && i < N; i++) {
+ if (abs(completions[i] - completions[i - 1]) > 1) {
+ fprintf(
+ stderr,
+ "bad completion size %d %d\n",
+ completions[i],
+ completions[i - 1]);
+ goto err;
+ }
+ }
+ return 0;
+err:
+ io_uring_queue_exit(&ring);
+ return 1;
+}
+
int main(int argc, char *argv[])
{
const char *fname = ".cq-overflow";
unsigned iters, drops;
unsigned long usecs;
int ret;
+ int i;
+ bool can_defer;
if (argc > 1)
return T_EXIT_SKIP;
+ can_defer = t_probe_defer_taskrun();
+ for (i = 0; i < 16; i++) {
+ bool batch = i & 1;
+ int mult = (i & 2) ? 1 : 2;
+ bool poll = i & 4;
+ bool defer = i & 8;
+
+ if (defer && !can_defer)
+ continue;
+
+ ret = test_overflow_handling(batch, mult, poll, defer);
+ if (ret) {
+ fprintf(stderr, "test_overflow_handling("
+ "batch=%d, mult=%d, poll=%d, defer=%d) failed\n",
+ batch, mult, poll, defer);
+ goto err;
+ }
+ }
+
ret = test_overflow();
if (ret) {
- printf("test_overflow failed\n");
+ fprintf(stderr, "test_overflow failed\n");
return ret;
}
--
2.30.2
