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Subject[PATCH 5.4 56/98] s390/qeth: fix af_iucv notification race
Date
From: Julian Wiedmann <jwi@linux.ibm.com>

[ Upstream commit 8908f36d20d8ba610d3a7d110b3049b5853b9bb1 ]

The two expected notification sequences are
1. TX_NOTIFY_PENDING with a subsequent TX_NOTIFY_DELAYED_*, when
our TX completion code first observed the pending TX and the QAOB
then completes at a later time; or
2. TX_NOTIFY_OK, when qeth_qdio_handle_aob() picked up the QAOB
completion before our TX completion code even noticed that the TX
was pending.

But as qeth_iqd_tx_complete() and qeth_qdio_handle_aob() can run
concurrently, we may end up with a race that results in a sequence of
TX_NOTIFY_DELAYED_* followed by TX_NOTIFY_PENDING. Which would confuse
the af_iucv code in its tracking of pending transmits.

Rework the notification code, so that qeth_qdio_handle_aob() defers its
notification if the TX completion code is still active.

Fixes: b333293058aa ("qeth: add support for af_iucv HiperSockets transport")
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/s390/net/qeth_core.h | 9 ++--
drivers/s390/net/qeth_core_main.c | 73 ++++++++++++++++++++++---------
2 files changed, 58 insertions(+), 24 deletions(-)

diff --git a/drivers/s390/net/qeth_core.h b/drivers/s390/net/qeth_core.h
index 820f2c29376c0..93b4cb156b0bc 100644
--- a/drivers/s390/net/qeth_core.h
+++ b/drivers/s390/net/qeth_core.h
@@ -436,10 +436,13 @@ enum qeth_qdio_out_buffer_state {
QETH_QDIO_BUF_EMPTY,
/* Filled by driver; owned by hardware in order to be sent. */
QETH_QDIO_BUF_PRIMED,
- /* Identified to be pending in TPQ. */
+ /* Discovered by the TX completion code: */
QETH_QDIO_BUF_PENDING,
- /* Found in completion queue. */
- QETH_QDIO_BUF_IN_CQ,
+ /* Finished by the TX completion code: */
+ QETH_QDIO_BUF_NEED_QAOB,
+ /* Received QAOB notification on CQ: */
+ QETH_QDIO_BUF_QAOB_OK,
+ QETH_QDIO_BUF_QAOB_ERROR,
/* Handled via transfer pending / completion queue. */
QETH_QDIO_BUF_HANDLED_DELAYED,
};
diff --git a/drivers/s390/net/qeth_core_main.c b/drivers/s390/net/qeth_core_main.c
index 6a2ac575e0a39..f07e73eb37ebb 100644
--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -438,6 +438,7 @@ static void qeth_cleanup_handled_pending(struct qeth_qdio_out_q *q, int bidx,
static void qeth_qdio_handle_aob(struct qeth_card *card,
unsigned long phys_aob_addr)
{
+ enum qeth_qdio_out_buffer_state new_state = QETH_QDIO_BUF_QAOB_OK;
struct qaob *aob;
struct qeth_qdio_out_buffer *buffer;
enum iucv_tx_notify notification;
@@ -449,22 +450,6 @@ static void qeth_qdio_handle_aob(struct qeth_card *card,
buffer = (struct qeth_qdio_out_buffer *) aob->user1;
QETH_CARD_TEXT_(card, 5, "%lx", aob->user1);

- if (atomic_cmpxchg(&buffer->state, QETH_QDIO_BUF_PRIMED,
- QETH_QDIO_BUF_IN_CQ) == QETH_QDIO_BUF_PRIMED) {
- notification = TX_NOTIFY_OK;
- } else {
- WARN_ON_ONCE(atomic_read(&buffer->state) !=
- QETH_QDIO_BUF_PENDING);
- atomic_set(&buffer->state, QETH_QDIO_BUF_IN_CQ);
- notification = TX_NOTIFY_DELAYED_OK;
- }
-
- if (aob->aorc != 0) {
- QETH_CARD_TEXT_(card, 2, "aorc%02X", aob->aorc);
- notification = qeth_compute_cq_notification(aob->aorc, 1);
- }
- qeth_notify_skbs(buffer->q, buffer, notification);
-
/* Free dangling allocations. The attached skbs are handled by
* qeth_cleanup_handled_pending().
*/
@@ -475,7 +460,33 @@ static void qeth_qdio_handle_aob(struct qeth_card *card,
kmem_cache_free(qeth_core_header_cache,
(void *) aob->sba[i]);
}
- atomic_set(&buffer->state, QETH_QDIO_BUF_HANDLED_DELAYED);
+
+ if (aob->aorc) {
+ QETH_CARD_TEXT_(card, 2, "aorc%02X", aob->aorc);
+ new_state = QETH_QDIO_BUF_QAOB_ERROR;
+ }
+
+ switch (atomic_xchg(&buffer->state, new_state)) {
+ case QETH_QDIO_BUF_PRIMED:
+ /* Faster than TX completion code. */
+ notification = qeth_compute_cq_notification(aob->aorc, 0);
+ qeth_notify_skbs(buffer->q, buffer, notification);
+ atomic_set(&buffer->state, QETH_QDIO_BUF_HANDLED_DELAYED);
+ break;
+ case QETH_QDIO_BUF_PENDING:
+ /* TX completion code is active and will handle the async
+ * completion for us.
+ */
+ break;
+ case QETH_QDIO_BUF_NEED_QAOB:
+ /* TX completion code is already finished. */
+ notification = qeth_compute_cq_notification(aob->aorc, 1);
+ qeth_notify_skbs(buffer->q, buffer, notification);
+ atomic_set(&buffer->state, QETH_QDIO_BUF_HANDLED_DELAYED);
+ break;
+ default:
+ WARN_ON_ONCE(1);
+ }

qdio_release_aob(aob);
}
@@ -1095,9 +1106,6 @@ static void qeth_tx_complete_buf(struct qeth_qdio_out_buffer *buf, bool error,
struct qeth_qdio_out_q *queue = buf->q;
struct sk_buff *skb;

- /* release may never happen from within CQ tasklet scope */
- WARN_ON_ONCE(atomic_read(&buf->state) == QETH_QDIO_BUF_IN_CQ);
-
if (atomic_read(&buf->state) == QETH_QDIO_BUF_PENDING)
qeth_notify_skbs(queue, buf, TX_NOTIFY_GENERALERROR);

@@ -5224,9 +5232,32 @@ static void qeth_iqd_tx_complete(struct qeth_qdio_out_q *queue,

if (atomic_cmpxchg(&buffer->state, QETH_QDIO_BUF_PRIMED,
QETH_QDIO_BUF_PENDING) ==
- QETH_QDIO_BUF_PRIMED)
+ QETH_QDIO_BUF_PRIMED) {
qeth_notify_skbs(queue, buffer, TX_NOTIFY_PENDING);

+ /* Handle race with qeth_qdio_handle_aob(): */
+ switch (atomic_xchg(&buffer->state,
+ QETH_QDIO_BUF_NEED_QAOB)) {
+ case QETH_QDIO_BUF_PENDING:
+ /* No concurrent QAOB notification. */
+ break;
+ case QETH_QDIO_BUF_QAOB_OK:
+ qeth_notify_skbs(queue, buffer,
+ TX_NOTIFY_DELAYED_OK);
+ atomic_set(&buffer->state,
+ QETH_QDIO_BUF_HANDLED_DELAYED);
+ break;
+ case QETH_QDIO_BUF_QAOB_ERROR:
+ qeth_notify_skbs(queue, buffer,
+ TX_NOTIFY_DELAYED_GENERALERROR);
+ atomic_set(&buffer->state,
+ QETH_QDIO_BUF_HANDLED_DELAYED);
+ break;
+ default:
+ WARN_ON_ONCE(1);
+ }
+ }
+
QETH_CARD_TEXT_(card, 5, "pel%u", bidx);

/* prepare the queue slot for re-use: */
--
2.27.0


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