netdev - [PATCH net 6/6] s390/qeth: fix IPA command submission race

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Message-Id: <20180227175817.84727-7-jwi@linux.vnet.ibm.com>
Date:   Tue, 27 Feb 2018 18:58:17 +0100
From:   Julian Wiedmann <jwi@...ux.vnet.ibm.com>
To:     David Miller <davem@...emloft.net>
Cc:     <netdev@...r.kernel.org>, <linux-s390@...r.kernel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Stefan Raspl <raspl@...ux.vnet.ibm.com>,
        Ursula Braun <ubraun@...ux.vnet.ibm.com>,
        Julian Wiedmann <jwi@...ux.vnet.ibm.com>
Subject: [PATCH net 6/6] s390/qeth: fix IPA command submission race

If multiple IPA commands are build & sent out concurrently,
fill_ipacmd_header() may assign a seqno value to a command that's
different from what send_control_data() later assigns to this command's
reply.
This is due to other commands passing through send_control_data(),
and incrementing card->seqno.ipa along the way.

So one IPA command has no reply that's waiting for its seqno, while some
other IPA command has multiple reply objects waiting for it.
Only one of those waiting replies wins, and the other(s) times out and
triggers a recovery via send_ipa_cmd().

Fix this by making sure that the same seqno value is assigned to
a command and its reply object.
Do so immediately before submitting the command & while holding the
irq_pending "lock", to produce nicely ascending seqnos.

As a side effect, *all* IPA commands now use a reply object that's
waiting for its actual seqno. Previously, early IPA commands that were
submitted while the card was still DOWN used the "catch-all" IDX seqno.

Signed-off-by: Julian Wiedmann <jwi@...ux.vnet.ibm.com>
---
 drivers/s390/net/qeth_core_main.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/drivers/s390/net/qeth_core_main.c b/drivers/s390/net/qeth_core_main.c
index 30457fca30c5..c8b308cfabf1 100644
--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -2134,24 +2134,25 @@ int qeth_send_control_data(struct qeth_card *card, int len,
 	}
 	reply->callback = reply_cb;
 	reply->param = reply_param;
-	if (card->state == CARD_STATE_DOWN)
-		reply->seqno = QETH_IDX_COMMAND_SEQNO;
-	else
-		reply->seqno = card->seqno.ipa++;
+
 	init_waitqueue_head(&reply->wait_q);
-	spin_lock_irqsave(&card->lock, flags);
-	list_add_tail(&reply->list, &card->cmd_waiter_list);
-	spin_unlock_irqrestore(&card->lock, flags);
 
 	while (atomic_cmpxchg(&card->write.irq_pending, 0, 1)) ;
-	qeth_prepare_control_data(card, len, iob);
 
 	if (IS_IPA(iob->data)) {
 		cmd = __ipa_cmd(iob);
+		cmd->hdr.seqno = card->seqno.ipa++;
+		reply->seqno = cmd->hdr.seqno;
 		event_timeout = QETH_IPA_TIMEOUT;
 	} else {
+		reply->seqno = QETH_IDX_COMMAND_SEQNO;
 		event_timeout = QETH_TIMEOUT;
 	}
+	qeth_prepare_control_data(card, len, iob);
+
+	spin_lock_irqsave(&card->lock, flags);
+	list_add_tail(&reply->list, &card->cmd_waiter_list);
+	spin_unlock_irqrestore(&card->lock, flags);
 
 	timeout = jiffies + event_timeout;
 
@@ -2933,7 +2934,7 @@ static void qeth_fill_ipacmd_header(struct qeth_card *card,
 	memset(cmd, 0, sizeof(struct qeth_ipa_cmd));
 	cmd->hdr.command = command;
 	cmd->hdr.initiator = IPA_CMD_INITIATOR_HOST;
-	cmd->hdr.seqno = card->seqno.ipa;
+	/* cmd->hdr.seqno is set by qeth_send_control_data() */
 	cmd->hdr.adapter_type = qeth_get_ipa_adp_type(card->info.link_type);
 	cmd->hdr.rel_adapter_no = (__u8) card->info.portno;
 	if (card->options.layer2)
-- 
2.13.5