[PATCH 2/4] fsx: fix infinite/too long loops when generating ranges for clone operations

[fdmanana@kernel.org]

From: Filipe Manana <fdmanana@suse.com>

While running generic/457 I've had fsx taking a lot of CPU time and not
making any progress for over an hour. Attaching gdb to the fsx process
revealed that fsx was in the loop that generates the ranges for a clone
operation, in particular the loop seemed to never end because the range
defined by 'offset2' kept overlapping with the range defined by 'offset'.
So far this happened two times in one of my test VMs with generic/457.

Fix this by breaking out of the loop after trying 30 times, like we
currently do for dedupe operations, which results in logging the operation
as skipped.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
---
 ltp/fsx.c | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/ltp/fsx.c b/ltp/fsx.c
index 56479eda..ab64b50a 100644
--- a/ltp/fsx.c
+++ b/ltp/fsx.c
@@ -2013,16 +2013,24 @@ test(void)
 			keep_size = random() % 2;
 		break;
 	case OP_CLONE_RANGE:
-		TRIM_OFF_LEN(offset, size, file_size);
-		offset = offset & ~(block_size - 1);
-		size = size & ~(block_size - 1);
-		do {
-			offset2 = random();
-			TRIM_OFF(offset2, maxfilelen);
-			offset2 = offset2 & ~(block_size - 1);
-		} while (range_overlaps(offset, offset2, size) ||
-			 offset2 + size > maxfilelen);
-		break;
+		{
+			int tries = 0;
+
+			TRIM_OFF_LEN(offset, size, file_size);
+			offset = offset & ~(block_size - 1);
+			size = size & ~(block_size - 1);
+			do {
+				if (tries++ >= 30) {
+					size = 0;
+					break;
+				}
+				offset2 = random();
+				TRIM_OFF(offset2, maxfilelen);
+				offset2 = offset2 & ~(block_size - 1);
+			} while (range_overlaps(offset, offset2, size) ||
+				 offset2 + size > maxfilelen);
+			break;
+		}
 	case OP_DEDUPE_RANGE:
 		{
 			int tries = 0;
-- 
2.11.0