block/008: avoid _offline_cpu() call in sub-shell

The helper function _offline_cpu() sets a value to RESTORE_CPUS_ONLINE.
However, the commit bd6b882b2650 ("block/008: check CPU offline failure
due to many IRQs") put _offline_cpu() call in sub-shell, then the set
value to RESTORE_CPUS_ONLINE no longer affects function caller's
environment. This resulted in offlined CPUs not restored by _cleanup()
when the test case block/008 calls only _offline_cpu() and does not call
_online_cpu().

To fix the issue, avoid _offline_cpu() call in sub-shell. Use file
redirect to get output of _offline_cpu() instead of sub-shell execution.

Fixes: bd6b882b2650 ("block/008: check CPU offline failure due to many IRQs")
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Link: https://lore.kernel.org/linux-block/20220703180956.2922025-1-yi.zhang@redhat.com/
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>

diff --git a/tests/block/008 b/tests/block/008
index 75aae6505a6136657a6804ce82dd6be3ad367edb..cd09352591577f868cac4f1be73ef5ca98c8c8f4 100755 (executable)
--- a/tests/block/008
+++ b/tests/block/008
@@ -34,6 +34,7 @@ test_device() {
        local offline_cpus=()
        local offlining=1
        local max_offline=${#HOTPLUGGABLE_CPUS[@]}
+       local o=$TMPDIR/offline_cpu_out
        if [[ ${#HOTPLUGGABLE_CPUS[@]} -eq ${#ALL_CPUS[@]} ]]; then
                (( max_offline-- ))
        fi
@@ -60,18 +61,18 @@ test_device() {
 
                if (( offlining )); then
                        idx=$((RANDOM % ${#online_cpus[@]}))
-                       if err=$(_offline_cpu "${online_cpus[$idx]}" 2>&1); then
+                       if _offline_cpu "${online_cpus[$idx]}" > "$o" 2>&1; then
                                offline_cpus+=("${online_cpus[$idx]}")
                                unset "online_cpus[$idx]"
                                online_cpus=("${online_cpus[@]}")
-                       elif [[ $err =~ "No space left on device" ]]; then
+                       elif [[ $(<"$o") =~ "No space left on device" ]]; then
                                # ENOSPC means CPU offline failure due to IRQ
                                # vector shortage. Keep current number of
                                # offline CPUs as maximum CPUs to offline.
                                max_offline=${#offline_cpus[@]}
                                offlining=0
                        else
-                               echo "Failed to offline CPU: $err"
+                               echo "Failed to offline CPU: $(<"$o")"
                                break
                        fi
                fi