2022-04-02 13:07:24

by Jakob Koschel

Subject: [PATCH 2/2] drbd: remove check of list iterator against head past the loop body

When list_for_each_entry() completes the iteration over the whole list
without breaking the loop, the iterator value will be a bogus pointer
computed based on the head element.

While it is safe to use the pointer to determine if it was computed
based on the head element, either with list_entry_is_head() or
&pos->member == head, using the iterator variable after the loop should
be avoided.

In preparation to limit the scope of a list iterator to the list
traversal loop, use a dedicated pointer to point to the found element [1].

Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
Signed-off-by: Jakob Koschel <[email protected]>
---
drivers/block/drbd/drbd_req.c | 42 ++++++++++++++++++++++-------------
1 file changed, 27 insertions(+), 15 deletions(-)

diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
index c04394518b07..b2571dc77fe6 100644
--- a/drivers/block/drbd/drbd_req.c
+++ b/drivers/block/drbd/drbd_req.c
@@ -332,17 +332,21 @@ static void set_if_null_req_next(struct drbd_peer_device *peer_device, struct dr
static void advance_conn_req_next(struct drbd_peer_device *peer_device, struct drbd_request *req)
{
struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
+ struct drbd_request *iter = req;
if (!connection)
return;
if (connection->req_next != req)
return;
- list_for_each_entry_continue(req, &connection->transfer_log, tl_requests) {
- const unsigned s = req->rq_state;
- if (s & RQ_NET_QUEUED)
+
+ req = NULL;
+ list_for_each_entry_continue(iter, &connection->transfer_log, tl_requests) {
+ const unsigned int s = iter->rq_state;
+
+ if (s & RQ_NET_QUEUED) {
+ req = iter;
break;
+ }
}
- if (&req->tl_requests == &connection->transfer_log)
- req = NULL;
connection->req_next = req;
}

@@ -358,17 +362,21 @@ static void set_if_null_req_ack_pending(struct drbd_peer_device *peer_device, st
static void advance_conn_req_ack_pending(struct drbd_peer_device *peer_device, struct drbd_request *req)
{
struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
+ struct drbd_request *iter = req;
if (!connection)
return;
if (connection->req_ack_pending != req)
return;
- list_for_each_entry_continue(req, &connection->transfer_log, tl_requests) {
- const unsigned s = req->rq_state;
- if ((s & RQ_NET_SENT) && (s & RQ_NET_PENDING))
+
+ req = NULL;
+ list_for_each_entry_continue(iter, &connection->transfer_log, tl_requests) {
+ const unsigned int s = iter->rq_state;
+
+ if ((s & RQ_NET_SENT) && (s & RQ_NET_PENDING)) {
+ req = iter;
break;
+ }
}
- if (&req->tl_requests == &connection->transfer_log)
- req = NULL;
connection->req_ack_pending = req;
}

@@ -384,17 +392,21 @@ static void set_if_null_req_not_net_done(struct drbd_peer_device *peer_device, s
static void advance_conn_req_not_net_done(struct drbd_peer_device *peer_device, struct drbd_request *req)
{
struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
+ struct drbd_request *iter = req;
if (!connection)
return;
if (connection->req_not_net_done != req)
return;
- list_for_each_entry_continue(req, &connection->transfer_log, tl_requests) {
- const unsigned s = req->rq_state;
- if ((s & RQ_NET_SENT) && !(s & RQ_NET_DONE))
+
+ req = NULL;
+ list_for_each_entry_continue(iter, &connection->transfer_log, tl_requests) {
+ const unsigned int s = iter->rq_state;
+
+ if ((s & RQ_NET_SENT) && !(s & RQ_NET_DONE)) {
+ req = iter;
break;
+ }
}
- if (&req->tl_requests == &connection->transfer_log)
- req = NULL;
connection->req_not_net_done = req;
}

--
2.25.1