[PATCH] add scsi_execute_in_process_context() API

We have several points in the SCSI stack (primarily for our device
functions) where we need to guarantee process context, but (given the
place where the last reference was released) we cannot guarantee this.

This API gets around the issue by executing the function directly if
the caller has process context, but scheduling a workqueue to execute
in process context if the caller doesn't have it.  Unfortunately, it
requires memory allocation in interrupt context, but it's better than
what we have previously.  The true solution will require a bit of
re-engineering, so isn't appropriate for 2.6.16.

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 4a602853a98e72f89b94757c4b9e56b87587ad53..4362dcde74afddaf797587b67b5a65c79d942599 100644 (file)
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -16,6 +16,7 @@
 #include <linux/init.h>
 #include <linux/pci.h>
 #include <linux/delay.h>
+#include <linux/hardirq.h>
 
 #include <scsi/scsi.h>
 #include <scsi/scsi_dbg.h>
@@ -2248,3 +2249,61 @@ scsi_target_unblock(struct device *dev)
                device_for_each_child(dev, NULL, target_unblock);
 }
 EXPORT_SYMBOL_GPL(scsi_target_unblock);
+
+
+struct work_queue_work {
+       struct work_struct      work;
+       void                    (*fn)(void *);
+       void                    *data;
+};
+
+static void execute_in_process_context_work(void *data)
+{
+       void (*fn)(void *data);
+       struct work_queue_work *wqw = data;
+
+       fn = wqw->fn;
+       data = wqw->data;
+
+       kfree(wqw);
+
+       fn(data);
+}
+
+/**
+ * scsi_execute_in_process_context - reliably execute the routine with user context
+ * @fn:                the function to execute
+ * @data:      data to pass to the function
+ *
+ * Executes the function immediately if process context is available,
+ * otherwise schedules the function for delayed execution.
+ *
+ * Returns:    0 - function was executed
+ *             1 - function was scheduled for execution
+ *             <0 - error
+ */
+int scsi_execute_in_process_context(void (*fn)(void *data), void *data)
+{
+       struct work_queue_work *wqw;
+
+       if (!in_interrupt()) {
+               fn(data);
+               return 0;
+       }
+
+       wqw = kmalloc(sizeof(struct work_queue_work), GFP_ATOMIC);
+
+       if (unlikely(!wqw)) {
+               printk(KERN_ERR "Failed to allocate memory\n");
+               WARN_ON(1);
+               return -ENOMEM;
+       }
+
+       INIT_WORK(&wqw->work, execute_in_process_context_work, wqw);
+       wqw->fn = fn;
+       wqw->data = data;
+       schedule_work(&wqw->work);
+
+       return 1;
+}
+EXPORT_SYMBOL_GPL(scsi_execute_in_process_context);

diff --git a/include/scsi/scsi.h b/include/scsi/scsi.h
index c60b8ff2f5e4f5d7a2952a8fb0951a689ec451b1..9c331258bc27a3792fdd90b23470e39cc168457d 100644 (file)
--- a/include/scsi/scsi.h
+++ b/include/scsi/scsi.h
@@ -433,4 +433,6 @@ struct scsi_lun {
 /* Used to obtain the PCI location of a device */
 #define SCSI_IOCTL_GET_PCI             0x5387
 
+int scsi_execute_in_process_context(void (*fn)(void *data), void *data);
+
 #endif /* _SCSI_SCSI_H */