[PATCH] xen: fix: use WARN_ON instead of if condition followed by BUG.

[PATCH] xen: fix: use WARN_ON instead of if condition followed by BUG.

[YANG LI]

Use WARN_ON instead of if condition followed by BUG in
gnttab_batch_map() and gnttab_batch_copy().

This issue was detected with the help of coccicheck.

Signed-off-by: YANG LI <abaci-bugfix@linux.alibaba.com>
Reported-by: Abaci <abaci@linux.alibaba.com>
---
 drivers/xen/grant-table.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 3729bea..db1770c 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -1080,8 +1080,8 @@ void gnttab_batch_map(struct gnttab_map_grant_ref *batch, unsigned count)
 {
 	struct gnttab_map_grant_ref *op;
 
-	if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, batch, count))
-		BUG();
+	WARN_ON(HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, batch, count));
+
 	for (op = batch; op < batch + count; op++)
 		if (op->status == GNTST_eagain)
 			gnttab_retry_eagain_gop(GNTTABOP_map_grant_ref, op,
@@ -1093,8 +1093,8 @@ void gnttab_batch_copy(struct gnttab_copy *batch, unsigned count)
 {
 	struct gnttab_copy *op;
 
-	if (HYPERVISOR_grant_table_op(GNTTABOP_copy, batch, count))
-		BUG();
+	WARN_ON(HYPERVISOR_grant_table_op(GNTTABOP_copy, batch, count));
+
 	for (op = batch; op < batch + count; op++)
 		if (op->status == GNTST_eagain)
 			gnttab_retry_eagain_gop(GNTTABOP_copy, op,
-- 
1.8.3.1

Re: [PATCH] xen: fix: use WARN_ON instead of if condition followed by BUG.

[Roger Pau Monné]

On Wed, Dec 30, 2020 at 02:38:06PM +0800, YANG LI wrote:
> Use WARN_ON instead of if condition followed by BUG in
> gnttab_batch_map() and gnttab_batch_copy().

But those are not equivalent as far as I'm aware. BUG will stop
execution, while WARN_ON will print a splat and continue executing.

If switching to WARN_ON is indeed fine it needs to be explained in the
commit message that returning to the caller(s) with
HYPERVISOR_grant_table_op having returned an error code is fine, and
that it's not going to create other issues, like memory corruption or
leaks.

Thanks, Roger.