qa: add script to stress udev_enumerate_scan_devices()

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

qa/suites/krbd/rbd-nomount/tasks/krbd_udev_enumerate.yaml

@@ -0,0 +1,5 @@
+tasks:
+- workunit:
+    clients:
+      all:
+        - rbd/krbd_udev_enumerate.sh

qa/workunits/rbd/krbd_udev_enumerate.sh

@@ -0,0 +1,66 @@
+#!/usr/bin/env bash
+
+# This is a test for https://tracker.ceph.com/issues/41036, but it also
+# triggers https://tracker.ceph.com/issues/41404 in some environments.
+
+set -ex
+
+function assert_exit_codes() {
+    declare -a pids=($@)
+
+    for pid in ${pids[@]}; do
+       wait $pid
+    done
+}
+
+function run_map() {
+    declare -a pids
+
+    for i in {1..300}; do
+        sudo rbd map img$i &
+        pids+=($!)
+    done
+
+    assert_exit_codes ${pids[@]}
+    [[ $(rbd showmapped | wc -l) -eq 301 ]]
+}
+
+function run_unmap_by_dev() {
+    declare -a pids
+
+    run_map
+    for i in {0..299}; do
+        sudo rbd unmap /dev/rbd$i &
+        pids+=($!)
+    done
+
+    assert_exit_codes ${pids[@]}
+    [[ $(rbd showmapped | wc -l) -eq 0 ]]
+}
+
+function run_unmap_by_spec() {
+    declare -a pids
+
+    run_map
+    for i in {1..300}; do
+        sudo rbd unmap img$i &
+        pids+=($!)
+    done
+
+    assert_exit_codes ${pids[@]}
+    [[ $(rbd showmapped | wc -l) -eq 0 ]]
+}
+
+# Can't test with exclusive-lock, don't bother enabling deep-flatten.
+# See https://tracker.ceph.com/issues/42492.
+for i in {1..300}; do
+    rbd create --size 1 --image-feature '' img$i
+done
+
+for i in {1..30}; do
+    echo Iteration $i
+    run_unmap_by_dev
+    run_unmap_by_spec
+done
+
+echo OK