Add simple fallocate test

Signed-off-by: Zach Brown <zab@versity.com>

tests/golden/fallocate

@@ -0,0 +1,3 @@
+== creating reasonably large per-mount files
+== 10s of racing cold reads and fallocate nop
+== cleaning up files

tests/sequence

@@ -4,6 +4,7 @@ inode-items-updated.sh
 simple-inode-index.sh
 simple-staging.sh
 simple-release-extents.sh
+fallocate.sh
 setattr_more.sh
 offline-extent-waiting.sh
 move-blocks.sh

tests/tests/fallocate.sh

@@ -0,0 +1,38 @@
+
+t_require_commands fallocate cat
+
+echo "== creating reasonably large per-mount files"
+for n in $(t_fs_nrs); do
+	eval path="\$T_D${n}/file-$n"
+
+	LC_ALL=C fallocate -l 128MiB  "$path" || \
+		t_fail "initial creating fallocate failed"
+done
+
+#
+# we had lock inversions between read and fallocate, dropping
+# the cache each time forces waiting for IO during the calls
+# with the inverted locks held so we have a better chance
+# of the deadlock happening.
+#
+DURATION=10
+echo "== ${DURATION}s of racing cold reads and fallocate nop"
+END=$((SECONDS + DURATION))
+while [ $SECONDS -le $END ]; do
+
+	echo 3 > /proc/sys/vm/drop_caches
+
+	for n in $(t_fs_nrs); do
+		eval path="\$T_D${n}/file-$n"
+		
+		LC_ALL=C fallocate -o 0 -l 4KiB  "$path" &
+		cat "$path" > /dev/null &
+	done
+
+	wait || t_fail "fallocate or cat failed"
+done
+
+echo "== cleaning up files"
+rm -f "$T_D0"/file-*
+
+t_pass