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Subject[PATCH 4.16 48/81] s390/qeth: avoid control IO completion stalls
Date
4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Julian Wiedmann <jwi@linux.vnet.ibm.com>


[ Upstream commit 901e3f49facbd31b2b3d1786637b4a35e1022e9b ]

For control IO, qeth currently tracks the index of the buffer that it
expects to complete the next IO on each qeth_channel. If the channel
presents an IRQ while this buffer has not yet completed, no completion
processing for _any_ completed buffer takes place.
So if the 'next buffer' is skipped for any sort of reason* (eg. when it
is released due to error conditions, before the IO is started), the
buffer obviously won't switch to PROCESSED until it is eventually
allocated for a _different_ IO and completes.
Until this happens, all completion processing on that channel stalls
and pending requests possibly time out.

As a fix, remove the whole 'next buffer' logic and simply process any
IO buffer right when it completes. A channel will never have more than
one IO pending, so there's no risk of processing out-of-sequence.

*Note: currently just one location in the code really handles this problem,
by advancing the 'next' index manually.

Signed-off-by: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/s390/net/qeth_core.h | 2 --
drivers/s390/net/qeth_core_main.c | 22 +++++-----------------
2 files changed, 5 insertions(+), 19 deletions(-)

--- a/drivers/s390/net/qeth_core.h
+++ b/drivers/s390/net/qeth_core.h
@@ -565,7 +565,6 @@ enum qeth_ip_types {
enum qeth_cmd_buffer_state {
BUF_STATE_FREE,
BUF_STATE_LOCKED,
- BUF_STATE_PROCESSED,
};

enum qeth_cq {
@@ -609,7 +608,6 @@ struct qeth_channel {
struct qeth_cmd_buffer iob[QETH_CMD_BUFFER_NO];
atomic_t irq_pending;
int io_buf_no;
- int buf_no;
};

/**
--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -821,7 +821,6 @@ void qeth_clear_cmd_buffers(struct qeth_

for (cnt = 0; cnt < QETH_CMD_BUFFER_NO; cnt++)
qeth_release_buffer(channel, &channel->iob[cnt]);
- channel->buf_no = 0;
channel->io_buf_no = 0;
}
EXPORT_SYMBOL_GPL(qeth_clear_cmd_buffers);
@@ -927,7 +926,6 @@ static int qeth_setup_channel(struct qet
kfree(channel->iob[cnt].data);
return -ENOMEM;
}
- channel->buf_no = 0;
channel->io_buf_no = 0;
atomic_set(&channel->irq_pending, 0);
spin_lock_init(&channel->iob_lock);
@@ -1103,11 +1101,9 @@ static void qeth_irq(struct ccw_device *
{
int rc;
int cstat, dstat;
- struct qeth_cmd_buffer *buffer;
struct qeth_channel *channel;
struct qeth_card *card;
struct qeth_cmd_buffer *iob;
- __u8 index;

if (__qeth_check_irb_error(cdev, intparm, irb))
return;
@@ -1185,25 +1181,18 @@ static void qeth_irq(struct ccw_device *
channel->state = CH_STATE_RCD_DONE;
goto out;
}
- if (intparm) {
- buffer = (struct qeth_cmd_buffer *) __va((addr_t)intparm);
- buffer->state = BUF_STATE_PROCESSED;
- }
if (channel == &card->data)
return;
if (channel == &card->read &&
channel->state == CH_STATE_UP)
__qeth_issue_next_read(card);

- iob = channel->iob;
- index = channel->buf_no;
- while (iob[index].state == BUF_STATE_PROCESSED) {
- if (iob[index].callback != NULL)
- iob[index].callback(channel, iob + index);
-
- index = (index + 1) % QETH_CMD_BUFFER_NO;
+ if (intparm) {
+ iob = (struct qeth_cmd_buffer *) __va((addr_t)intparm);
+ if (iob->callback)
+ iob->callback(iob->channel, iob);
}
- channel->buf_no = index;
+
out:
wake_up(&card->wait_q);
return;
@@ -2217,7 +2206,6 @@ time_err:
error:
atomic_set(&card->write.irq_pending, 0);
qeth_release_buffer(iob->channel, iob);
- card->write.buf_no = (card->write.buf_no + 1) % QETH_CMD_BUFFER_NO;
rc = reply->rc;
qeth_put_reply(reply);
return rc;

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