[PATCH blktests] Add a test that triggers the blk_mq_realloc_hw_ctxs() error path

[Bart Van Assche <bvanassche@acm.org>]

Add a test that triggers the code touched by commit d0930bb8f46b ("blk-mq:
Fix a recently introduced regression in blk_mq_realloc_hw_ctxs()"). This
test only runs if a recently added fault injection feature is available,
namely commit 596444e75705 ("null_blk: Add support for init_hctx() fault
injection").

Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 tests/block/030     | 55 +++++++++++++++++++++++++++++++++++++++++++++
 tests/block/030.out |  1 +
 2 files changed, 56 insertions(+)
 create mode 100755 tests/block/030
 create mode 100644 tests/block/030.out

diff --git a/tests/block/030 b/tests/block/030
new file mode 100755
index 000000000000..028b0a1a6e9a
--- /dev/null
+++ b/tests/block/030
@@ -0,0 +1,55 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright 2020 Google LLC
+#
+# Trigger the blk_mq_realloc_hw_ctxs() error path.
+
+. tests/block/rc
+. common/null_blk
+
+DESCRIPTION="trigger the blk_mq_realloc_hw_ctxs() error path"
+QUICK=1
+
+requires() {
+	_have_null_blk || return $?
+	_have_module_param null_blk init_hctx || return $?
+}
+
+# Configure one null_blk instance.
+configure_null_blk() {
+	local nullb0="/sys/kernel/config/nullb/nullb0"
+
+	mkdir "$nullb0" &&
+	echo 0 > "$nullb0/completion_nsec" &&
+	echo 512 > "$nullb0/blocksize" &&
+	echo 16 > "$nullb0/size" &&
+	nproc > "$nullb0/submit_queues" &&
+	echo 1 > "$nullb0/memory_backed" &&
+	echo 1 > "$nullb0/power" &&
+	ls -l /dev/nullb* &>>"$FULL"
+}
+
+test() {
+	local i sq=/sys/kernel/config/nullb/nullb0/submit_queues
+
+	: "${TIMEOUT:=30}"
+	if ! _init_null_blk nr_devices=0 queue_mode=2 "init_hctx=$(nproc),100,0,0"; then
+		echo "Loading null_blk failed"
+		return 1
+	fi
+	if ! configure_null_blk; then
+		echo "Configuring null_blk failed"
+		return 1
+	fi
+	if { echo "$(<"$sq")" >$sq; } 2>/dev/null; then
+		for ((i=0;i<100;i++)); do
+			echo 1 >$sq
+			nproc >$sq
+		done
+	else
+		echo "Skipping test because $sq cannot be modified" >>"$FULL"
+	fi
+	rmdir /sys/kernel/config/nullb/nullb0
+	_exit_null_blk
+	echo Passed
+}
diff --git a/tests/block/030.out b/tests/block/030.out
new file mode 100644
index 000000000000..863339fb8ced
--- /dev/null
+++ b/tests/block/030.out
@@ -0,0 +1 @@
+Passed