Patch "s390/qeth: fix IPA command submission race" has been added to the 4.15-stable tree

This is a note to let you know that I've just added the patch titled

s390/qeth: fix IPA command submission race

to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
s390-qeth-fix-ipa-command-submission-race.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Julian Wiedmann <[email protected]>
Date: Tue, 27 Feb 2018 18:58:17 +0100
Subject: s390/qeth: fix IPA command submission race

From: Julian Wiedmann <[email protected]>

[ Upstream commit d22ffb5a712f9211ffd104c38fc17cbfb1b5e2b0 ]

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.

---
 drivers/s390/net/qeth_core_main.c |   19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

@@ -2071,24 +2071,25 @@ int qeth_send_control_data(struct qeth_c
 	}
 	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;
 

@@ -2870,7 +2871,7 @@ static void qeth_fill_ipacmd_header(stru
 	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)

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/s390-qeth-fix-setip-command-handling.patch queue-4.15/s390-qeth-fix-ip-address-lookup-for-l3-devices.patch queue-4.15/s390-qeth-fix-ipa-command-submission-race.patch queue-4.15/revert-s390-qeth-fix-using-of-ref-counter-for-rxip-addresses.patch queue-4.15/s390-qeth-fix-overestimated-count-of-buffer-elements.patch queue-4.15/s390-qeth-fix-double-free-on-ip-add-remove-race.patch queue-4.15/s390-qeth-fix-ip-removal-on-offline-cards.patch queue-4.15/s390-qeth-fix-underestimated-count-of-buffer-elements.patch