s390/qeth: avoid control IO completion stalls

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>

diff --git a/drivers/s390/net/qeth_core.h b/drivers/s390/net/qeth_core.h
index 4326715dc13eb18af4c69cc233f279ab264fae36..78b98b3e7efaf3893d0451ca6524220c94a26994 100644 (file)
--- a/drivers/s390/net/qeth_core.h
+++ b/drivers/s390/net/qeth_core.h
@@ -557,7 +557,6 @@ enum qeth_prot_versions {
 enum qeth_cmd_buffer_state {
        BUF_STATE_FREE,
        BUF_STATE_LOCKED,
-       BUF_STATE_PROCESSED,
 };
 
 enum qeth_cq {
@@ -601,7 +600,6 @@ struct qeth_channel {
        struct qeth_cmd_buffer iob[QETH_CMD_BUFFER_NO];
        atomic_t irq_pending;
        int io_buf_no;
-       int buf_no;
 };
 
 /**

diff --git a/drivers/s390/net/qeth_core_main.c b/drivers/s390/net/qeth_core_main.c
index 36bc94088de1e5090d8cfe7ae38a6e2cd7e70d25..5ec47c6ebaa64d74fba9ee1bd4c3390de9e353fd 100644 (file)
--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -818,7 +818,6 @@ void qeth_clear_cmd_buffers(struct qeth_channel *channel)
 
        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);
@@ -924,7 +923,6 @@ static int qeth_setup_channel(struct qeth_channel *channel)
                        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);
@@ -1100,11 +1098,9 @@ static void qeth_irq(struct ccw_device *cdev, unsigned long intparm,
 {
        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;
@@ -1182,25 +1178,18 @@ static void qeth_irq(struct ccw_device *cdev, unsigned long intparm,
                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;
@@ -2214,7 +2203,6 @@ 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;