[PULL 12/32] block/file-posix: Fix check_cache_dropped() error handling

[Markus Armbruster <armbru@redhat.com>]

The Error ** argument must be NULL, &error_abort, &error_fatal, or a
pointer to a variable containing NULL.  Passing an argument of the
latter kind twice without clearing it in between is wrong: if the
first call sets an error, it no longer points to NULL for the second
call.

check_cache_dropped() calls error_setg() in a loop.  It fails to break
the loop in one instance.  If a subsequent iteration error_setg()s
again, it trips error_setv()'s assertion.

Fix it to break the loop.

Fixes: 31be8a2a97ecba7d31a82932286489cac318e9e9
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200422130719.28225-3-armbru@redhat.com>
---
 block/file-posix.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index 7e19bbff5f..094e3b0212 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -2691,10 +2691,13 @@ static void check_cache_dropped(BlockDriverState *bs, Error **errp)
         vec_end = DIV_ROUND_UP(length, page_size);
         for (i = 0; i < vec_end; i++) {
             if (vec[i] & 0x1) {
-                error_setg(errp, "page cache still in use!");
                 break;
             }
         }
+        if (i < vec_end) {
+            error_setg(errp, "page cache still in use!");
+            break;
+        }
     }
 
     if (window) {
-- 
2.21.1