Add a test that triggers the blk_mq_realloc_hw_ctxs() error path

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>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>

diff --git a/tests/block/030 b/tests/block/030
new file mode 100755 (executable)
index 0000000..84302c1
--- /dev/null
+++ b/tests/block/030
@@ -0,0 +1,53 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright 2020 Google LLC
+#
+# Trigger the blk_mq_realloc_hw_ctxs() error path. Regression test for commit
+# d0930bb8f46b ("blk-mq: Fix a recently introduced regression in
+# blk_mq_realloc_hw_ctxs()").
+
+. tests/block/rc
+. common/null_blk
+
+DESCRIPTION="trigger the blk_mq_realloc_hw_ctxs() error path"
+QUICK=1
+
+requires() {
+       _have_null_blk && _have_module_param null_blk init_hctx
+}
+
+test() {
+       local i sq=/sys/kernel/config/nullb/nullb0/submit_queues
+
+       : "${TIMEOUT:=30}"
+       # Legend: init_hctx=<interval>,<probability>,<space>,<times>
+       # Set <space> to $(nproc) + 1 to make loading of null_blk succeed.
+       if ! _init_null_blk nr_devices=0 queue_mode=2 \
+            "init_hctx=$(nproc),100,$(($(nproc) + 1)),-1"; then
+               echo "Loading null_blk failed"
+               return 1
+       fi
+       if ! _configure_null_blk nullb0 completion_nsec=0 blocksize=512 size=16\
+            submit_queues="$(nproc)" memory_backed=1 power=1; then
+               echo "Configuring null_blk failed"
+               return 1
+       fi
+       # Since older null_blk versions do not allow "submit_queues" to be
+       # modified, check first whether that configs attribute is writeable.
+       # Each iteration of the loop below triggers $(nproc) + 1
+       # null_init_hctx() calls. Since <interval>=$(nproc), all possible
+       # blk_mq_realloc_hw_ctxs() error paths will be triggered. Whether or
+       # not this test succeeds depends on whether or not _check_dmesg()
+       # detects a kernel warning.
+       if { echo "$(<"$sq")" >$sq; } 2>/dev/null; then
+               for ((i = 0; i < 100; i++)); do
+                       echo 1 > $sq
+                       nproc > $sq
+               done
+       else
+               SKIP_REASON="Skipping test because $sq cannot be modified"
+       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 (file)
index 0000000..863339f
--- /dev/null
+++ b/tests/block/030.out
@@ -0,0 +1 @@
+Passed