scsi: zfcp: Lift Input Queue tasklet from qdio

Shift the IRQ tasklet processing from the qdio layer into zfcp.  This will
allow for a good amount of cleanups in qdio, and provides future
opportunity to improve the IRQ processing inside zfcp.

We continue to use the qdio layer's internal tasklet/timer mechanism
(ie. scan_threshold etc) to check for Request Queue completions.  Initially
we planned to check for such completions after inspecting the Response
Queue - this should typically work, but there's a theoretical race where
the device only presents the Request Queue completions _after_ all Response
Queue processing has finished.  If the Request Queue is then also
_completely_ full, we could send no further IOs and thus get no interrupt
that would trigger an inspection of the Request Queue.  So for now stick to
the old model, where we can trust that such a race would be recovered by
qdio's internal timer.

Code-flow wise, this establishes two levels of control:

1. The qdio layer will only deliver IRQs to the device driver if the
   QDIO_IRQ_DISABLED flag is cleared. zfcp manages this through
   qdio_start_irq() / qdio_stop_irq(). The initial state is DISABLED, and
   zfcp_qdio_open() schedules zfcp's IRQ tasklet once during startup to
   explicitly enable IRQ delivery.

2. The zfcp tasklet is initialized with tasklet_disable(), and only gets
   enabled once we open the qdio device.  When closing the qdio device, we
   must disable the tasklet _before_ disabling IRQ delivery (otherwise a
   concurrently running tasklet could re-enable IRQ delivery after we
   disabled it).

   A final tasklet_kill() during teardown ensures that no lingering
   tasklet_schedule() is still accessing the tasklet structure.

Link: https://lore.kernel.org/r/94a765211c48b74a7b91c5e60b158de01db98d43.1603908167.git.bblock@linux.ibm.com
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/s390/scsi/zfcp_qdio.c b/drivers/s390/scsi/zfcp_qdio.c
index a8a51407408484b018fb7af783db765cdc7208ed..9fc045ddf66dba37e964d771c410f8eeff2eb976 100644 (file)
--- a/drivers/s390/scsi/zfcp_qdio.c
+++ b/drivers/s390/scsi/zfcp_qdio.c
@@ -131,6 +131,33 @@ static void zfcp_qdio_int_resp(struct ccw_device *cdev, unsigned int qdio_err,
                zfcp_erp_adapter_reopen(qdio->adapter, 0, "qdires2");
 }
 
+static void zfcp_qdio_irq_tasklet(struct tasklet_struct *tasklet)
+{
+       struct zfcp_qdio *qdio = from_tasklet(qdio, tasklet, irq_tasklet);
+       struct ccw_device *cdev = qdio->adapter->ccw_device;
+       unsigned int start, error;
+       int completed;
+
+       /* Check the Response Queue, and kick off the Request Queue tasklet: */
+       completed = qdio_get_next_buffers(cdev, 0, &start, &error);
+       if (completed < 0)
+               return;
+       if (completed > 0)
+               zfcp_qdio_int_resp(cdev, error, 0, start, completed,
+                                  (unsigned long) qdio);
+
+       if (qdio_start_irq(cdev))
+               /* More work pending: */
+               tasklet_schedule(&qdio->irq_tasklet);
+}
+
+static void zfcp_qdio_poll(struct ccw_device *cdev, unsigned long data)
+{
+       struct zfcp_qdio *qdio = (struct zfcp_qdio *) data;
+
+       tasklet_schedule(&qdio->irq_tasklet);
+}
+
 static struct qdio_buffer_element *
 zfcp_qdio_sbal_chain(struct zfcp_qdio *qdio, struct zfcp_qdio_req *q_req)
 {
@@ -332,6 +359,8 @@ void zfcp_qdio_close(struct zfcp_qdio *qdio)
 
        wake_up(&qdio->req_q_wq);
 
+       tasklet_disable(&qdio->irq_tasklet);
+       qdio_stop_irq(adapter->ccw_device);
        qdio_shutdown(adapter->ccw_device, QDIO_FLAG_CLEANUP_USING_CLEAR);
 
        /* cleanup used outbound sbals */
@@ -387,6 +416,7 @@ int zfcp_qdio_open(struct zfcp_qdio *qdio)
        init_data.no_output_qs = 1;
        init_data.input_handler = zfcp_qdio_int_resp;
        init_data.output_handler = zfcp_qdio_int_req;
+       init_data.irq_poll = zfcp_qdio_poll;
        init_data.int_parm = (unsigned long) qdio;
        init_data.input_sbal_addr_array = input_sbals;
        init_data.output_sbal_addr_array = output_sbals;
@@ -433,6 +463,11 @@ int zfcp_qdio_open(struct zfcp_qdio *qdio)
        atomic_set(&qdio->req_q_free, QDIO_MAX_BUFFERS_PER_Q);
        atomic_or(ZFCP_STATUS_ADAPTER_QDIOUP, &qdio->adapter->status);
 
+       /* Enable processing for QDIO interrupts: */
+       tasklet_enable(&qdio->irq_tasklet);
+       /* This results in a qdio_start_irq(): */
+       tasklet_schedule(&qdio->irq_tasklet);
+
        zfcp_qdio_shost_update(adapter, qdio);
 
        return 0;
@@ -450,6 +485,8 @@ void zfcp_qdio_destroy(struct zfcp_qdio *qdio)
        if (!qdio)
                return;
 
+       tasklet_kill(&qdio->irq_tasklet);
+
        if (qdio->adapter->ccw_device)
                qdio_free(qdio->adapter->ccw_device);
 
@@ -475,6 +512,8 @@ int zfcp_qdio_setup(struct zfcp_adapter *adapter)
 
        spin_lock_init(&qdio->req_q_lock);
        spin_lock_init(&qdio->stat_lock);
+       tasklet_setup(&qdio->irq_tasklet, zfcp_qdio_irq_tasklet);
+       tasklet_disable(&qdio->irq_tasklet);
 
        adapter->qdio = qdio;
        return 0;

diff --git a/drivers/s390/scsi/zfcp_qdio.h b/drivers/s390/scsi/zfcp_qdio.h
index 6b43d6b254bef2e34757a4bafe92bc3d0a19129a..9c1f310db1551b8a077dddf599276388004bd2ae 100644 (file)
--- a/drivers/s390/scsi/zfcp_qdio.h
+++ b/drivers/s390/scsi/zfcp_qdio.h
@@ -10,6 +10,7 @@
 #ifndef ZFCP_QDIO_H
 #define ZFCP_QDIO_H
 
+#include <linux/interrupt.h>
 #include <asm/qdio.h>
 
 #define ZFCP_QDIO_SBALE_LEN    PAGE_SIZE
@@ -44,6 +45,7 @@ struct zfcp_qdio {
        u64                     req_q_util;
        atomic_t                req_q_full;
        wait_queue_head_t       req_q_wq;
+       struct tasklet_struct   irq_tasklet;
        struct zfcp_adapter     *adapter;
        u16                     max_sbale_per_sbal;
        u16                     max_sbale_per_req;