[SRU][N:linux-azure][PATCH 1/1] cifs: reset iface weights when we cannot find a candidate

[Vinicius Peixoto]

From: Shyam Prasad N <sprasad at microsoft.com>

BugLink: https://bugs.launchpad.net/bugs/2127706

We now do a weighted selection of server interfaces when allocating
new channels. The weights are decided based on the speed advertised.
The fulfilled weight for an interface is a counter that is used to
track the interface selection. It should be reset back to zero once
all interfaces fulfilling their weight.

In cifs_chan_update_iface, this reset logic was missing. As a result
when the server interface list changes, the client may not be able
to find a new candidate for other channels after all interfaces have
been fulfilled.

Fixes: a6d8fb54a515 ("cifs: distribute channels across interfaces based on speed")
Cc: <stable at vger.kernel.org>
Signed-off-by: Shyam Prasad N <sprasad at microsoft.com>
Signed-off-by: Steve French <stfrench at microsoft.com>
(cherry picked from commit 9d5eff7821f6d70f7d1b4d8a60680fba4de868a7)
Signed-off-by: Vinicius Peixoto <vinicius.peixoto at canonical.com>
---
 fs/smb/client/sess.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/smb/client/sess.c b/fs/smb/client/sess.c
index 96de4f1a91a5..0f5d3e00373c 100644
--- a/fs/smb/client/sess.c
+++ b/fs/smb/client/sess.c
@@ -372,6 +372,7 @@ cifs_chan_update_iface(struct cifs_ses *ses, struct TCP_Server_Info *server)
 	struct cifs_server_iface *old_iface = NULL;
 	struct cifs_server_iface *last_iface = NULL;
 	struct sockaddr_storage ss;
+	int retry = 0;
 
 	spin_lock(&ses->chan_lock);
 	chan_index = cifs_ses_get_chan_index(ses, server);
@@ -400,6 +401,7 @@ cifs_chan_update_iface(struct cifs_ses *ses, struct TCP_Server_Info *server)
 		return;
 	}
 
+try_again:
 	last_iface = list_last_entry(&ses->iface_list, struct cifs_server_iface,
 				     iface_head);
 	iface_min_speed = last_iface->speed;
@@ -437,6 +439,13 @@ cifs_chan_update_iface(struct cifs_ses *ses, struct TCP_Server_Info *server)
 	}
 
 	if (list_entry_is_head(iface, &ses->iface_list, iface_head)) {
+		list_for_each_entry(iface, &ses->iface_list, iface_head)
+			iface->weight_fulfilled = 0;
+
+		/* see if it can be satisfied in second attempt */
+		if (!retry++)
+			goto try_again;
+
 		iface = NULL;
 		cifs_dbg(FYI, "unable to find a suitable iface\n");
 	}
-- 
2.45.2