[PATCH 1/2] selftests: ublk: don't keep the fault_inject timespec on the stack

[Qiliang Yuan]

The fault_inject target delays each I/O with an IORING_OP_TIMEOUT, and
generic_06 relies on the delay to kill the server while an I/O is still
outstanding.

The timespec of the timeout is a local variable of
ublk_fault_inject_queue_io(). The SQE only records its address, and
io_uring reads it when the SQE is submitted, after the function has
returned. The timeout gets whatever the stack holds by then and expires
almost at once, so --delay_us has no effect, and generic_06 fails
because dd completes before the server is killed.

Store the timespec in the per-device fi_opts, and split the delay into
seconds and nanoseconds so that delays of a second or more give a valid
timespec.

fio 4k random reads for 10 s at queue depth 1 on a fault_inject device
with --delay_us 1000000:

                  before      after   expected
  I/Os            446927         10         10
  mean latency   18.3 us    1.000 s        1 s

Fixes: 81586652bb1f ("selftests: ublk: add generic_06 for covering fault inject")
Signed-off-by: Qiliang Yuan <odys.yuan@xxxxxxxxx>
---
 tools/testing/selftests/ublk/fault_inject.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/ublk/fault_inject.c b/tools/testing/selftests/ublk/fault_inject.c
index 150896e02ff8b..e055f51a65447 100644
--- a/tools/testing/selftests/ublk/fault_inject.c
+++ b/tools/testing/selftests/ublk/fault_inject.c
@@ -11,7 +11,7 @@
 #include "kublk.h"
 
 struct fi_opts {
-	long long delay_ns;
+	struct __kernel_timespec delay;
 	bool die_during_fetch;
 };
 
@@ -47,7 +47,8 @@ static int ublk_fault_inject_tgt_init(const struct dev_ctx *ctx,
 		return -ENOMEM;
 	}
 
-	opts->delay_ns = ctx->fault_inject.delay_us * 1000;
+	opts->delay.tv_sec = ctx->fault_inject.delay_us / 1000000;
+	opts->delay.tv_nsec = ctx->fault_inject.delay_us % 1000000 * 1000;
 	opts->die_during_fetch = ctx->fault_inject.die_during_fetch;
 	dev->private_data = opts;
 
@@ -85,12 +86,13 @@ static int ublk_fault_inject_queue_io(struct ublk_thread *t,
 	const struct ublksrv_io_desc *iod = ublk_get_iod(q, tag);
 	struct io_uring_sqe *sqe;
 	struct fi_opts *opts = q->dev->private_data;
-	struct __kernel_timespec ts = {
-		.tv_nsec = opts->delay_ns,
-	};
 
+	/*
+	 * Pass a timespec that outlives this function, since io_uring
+	 * reads it only when the SQE is submitted.
+	 */
 	ublk_io_alloc_sqes(t, &sqe, 1);
-	io_uring_prep_timeout(sqe, &ts, 1, 0);
+	io_uring_prep_timeout(sqe, &opts->delay, 1, 0);
 	sqe->user_data = build_user_data(tag, ublksrv_get_op(iod), 0, q->q_id, 1);
 
 	ublk_queued_tgt_io(t, q, tag, 1);

-- 
2.43.0