cifs: don't call mid_q_entry->callback under the Global_MidLock (try #5)

Minor revision to the last version of this patch -- the only difference
is the fix to the cFYI statement in cifs_reconnect.

Holding the spinlock while we call this function means that it can't
sleep, which really limits what it can do. Taking it out from under
the spinlock also means less contention for this global lock.

Change the semantics such that the Global_MidLock is not held when
the callback is called. To do this requires that we take extra care
not to have sync_mid_result remove the mid from the list when the
mid is in a state where that has already happened. This prevents
list corruption when the mid is sitting on a private list for
reconnect or when cifsd is coming down.

Reviewed-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Reviewed-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 24 insertions, 6 deletions

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 273cf42b2915..6070ba69647b 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -137,6 +137,7 @@ cifs_reconnect(struct TCP_Server_Info *server)
 	struct cifsSesInfo *ses;
 	struct cifsTconInfo *tcon;
 	struct mid_q_entry *mid_entry;
+	struct list_head retry_list;
 
 	spin_lock(&GlobalMid_Lock);
 	if (server->tcpStatus == CifsExiting) {
@@ -188,16 +189,23 @@ cifs_reconnect(struct TCP_Server_Info *server)
 	mutex_unlock(&server->srv_mutex);
 
 	/* mark submitted MIDs for retry and issue callback */
-	cFYI(1, "%s: issuing mid callbacks", __func__);
+	INIT_LIST_HEAD(&retry_list);
+	cFYI(1, "%s: moving mids to private list", __func__);
 	spin_lock(&GlobalMid_Lock);
 	list_for_each_safe(tmp, tmp2, &server->pending_mid_q) {
 		mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
 		if (mid_entry->midState == MID_REQUEST_SUBMITTED)
 			mid_entry->midState = MID_RETRY_NEEDED;
+		list_move(&mid_entry->qhead, &retry_list);
+	}
+	spin_unlock(&GlobalMid_Lock);
+
+	cFYI(1, "%s: issuing mid callbacks", __func__);
+	list_for_each_safe(tmp, tmp2, &retry_list) {
+		mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
 		list_del_init(&mid_entry->qhead);
 		mid_entry->callback(mid_entry);
 	}
-	spin_unlock(&GlobalMid_Lock);
 
 	while (server->tcpStatus == CifsNeedReconnect) {
 		try_to_freeze();
@@ -671,12 +679,12 @@ multi_t2_fnd:
 			mid_entry->when_received = jiffies;
 #endif
 			list_del_init(&mid_entry->qhead);
-			mid_entry->callback(mid_entry);
 			break;
 		}
 		spin_unlock(&GlobalMid_Lock);
 
 		if (mid_entry != NULL) {
+			mid_entry->callback(mid_entry);
 			/* Was previous buf put in mpx struct for multi-rsp? */
 			if (!isMultiRsp) {
 				/* smb buffer will be freed by user thread */
@@ -740,15 +748,25 @@ multi_t2_fnd:
 		cifs_small_buf_release(smallbuf);
 
 	if (!list_empty(&server->pending_mid_q)) {
+		struct list_head dispose_list;
+
+		INIT_LIST_HEAD(&dispose_list);
 		spin_lock(&GlobalMid_Lock);
 		list_for_each_safe(tmp, tmp2, &server->pending_mid_q) {
 			mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
-			cFYI(1, "Clearing Mid 0x%x - issuing callback",
-					 mid_entry->mid);
+			cFYI(1, "Clearing mid 0x%x", mid_entry->mid);
+			mid_entry->midState = MID_SHUTDOWN;
+			list_move(&mid_entry->qhead, &dispose_list);
+		}
+		spin_unlock(&GlobalMid_Lock);
+
+		/* now walk dispose list and issue callbacks */
+		list_for_each_safe(tmp, tmp2, &dispose_list) {
+			mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
+			cFYI(1, "Callback mid 0x%x", mid_entry->mid);
 			list_del_init(&mid_entry->qhead);
 			mid_entry->callback(mid_entry);
 		}
-		spin_unlock(&GlobalMid_Lock);
 		/* 1/8th of sec is more than enough time for them to exit */
 		msleep(125);
 	}