USB: update spinlock usage for root-hub URBs

This patch (as952) adjusts the spinlock usage in the root-hub
emulation part of usbcore, to make it match more closely the pattern
used by regular host controller drivers.  To wit: The private lock
(usb_hcd_root_hub_lock) is held throughout the important parts, and it
is dropped temporarily without re-enabling interrupts around the call
to usb_hcd_giveback_urb().

A nice side effect is that the code now avoids calling
local_irq_save(), thereby becoming more RT-friendly.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 29 insertions, 23 deletions

diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index 47a055a2acf5..f8e7deb03ee9 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -356,10 +356,11 @@ static int rh_call_control (struct usb_hcd *hcd, struct urb *urb)
         const u8        *bufp = tbuf;
         int             len = 0;
         int             patch_wakeup = 0;
-        unsigned long   flags;
         int             status = 0;
         int             n;
 
+        might_sleep();
+
         cmd = (struct usb_ctrlrequest *) urb->setup_packet;
         typeReq  = (cmd->bRequestType << 8) | cmd->bRequest;
         wValue   = le16_to_cpu (cmd->wValue);
@@ -523,13 +524,21 @@ error:
         }
 
         /* any errors get returned through the urb completion */
-        local_irq_save (flags);
-        spin_lock (&urb->lock);
+        spin_lock_irq(&hcd_root_hub_lock);
+        spin_lock(&urb->lock);
         if (urb->status == -EINPROGRESS)
                 urb->status = status;
-        spin_unlock (&urb->lock);
-        usb_hcd_giveback_urb (hcd, urb);
-        local_irq_restore (flags);
+        spin_unlock(&urb->lock);
+
+        /* This peculiar use of spinlocks echoes what real HC drivers do.
+         * Avoiding calls to local_irq_disable/enable makes the code
+         * RT-friendly.
+         */
+        spin_unlock(&hcd_root_hub_lock);
+        usb_hcd_giveback_urb(hcd, urb);
+        spin_lock(&hcd_root_hub_lock);
+
+        spin_unlock_irq(&hcd_root_hub_lock);
         return 0;
 }
 
@@ -559,8 +568,7 @@ void usb_hcd_poll_rh_status(struct usb_hcd *hcd)
         if (length > 0) {
 
                 /* try to complete the status urb */
-                local_irq_save (flags);
-                spin_lock(&hcd_root_hub_lock);
+                spin_lock_irqsave(&hcd_root_hub_lock, flags);
                 urb = hcd->status_urb;
                 if (urb) {
                         spin_lock(&urb->lock);
@@ -574,16 +582,16 @@ void usb_hcd_poll_rh_status(struct usb_hcd *hcd)
                         } else          /* urb has been unlinked */
                                 length = 0;
                         spin_unlock(&urb->lock);
+
+                        spin_unlock(&hcd_root_hub_lock);
+                        usb_hcd_giveback_urb(hcd, urb);
+                        spin_lock(&hcd_root_hub_lock);
                 } else
                         length = 0;
-                spin_unlock(&hcd_root_hub_lock);
 
-                /* local irqs are always blocked in completions */
-                if (length > 0)
-                        usb_hcd_giveback_urb (hcd, urb);
-                else
+                if (length <= 0)
                         hcd->poll_pending = 1;
-                local_irq_restore (flags);
+                spin_unlock_irqrestore(&hcd_root_hub_lock, flags);
         }
 
         /* The USB 2.0 spec says 256 ms.  This is close enough and won't
@@ -651,25 +659,23 @@ static int usb_rh_urb_dequeue (struct usb_hcd *hcd, struct urb *urb)
 {
         unsigned long   flags;
 
+        spin_lock_irqsave(&hcd_root_hub_lock, flags);
         if (usb_endpoint_num(&urb->ep->desc) == 0) {    /* Control URB */
                 ;       /* Do nothing */
 
         } else {                                /* Status URB */
                 if (!hcd->uses_new_polling)
                         del_timer (&hcd->rh_timer);
-                local_irq_save (flags);
-                spin_lock (&hcd_root_hub_lock);
                 if (urb == hcd->status_urb) {
                         hcd->status_urb = NULL;
                         urb->hcpriv = NULL;
-                } else
-                        urb = NULL;             /* wasn't fully queued */
-                spin_unlock (&hcd_root_hub_lock);
-                if (urb)
-                        usb_hcd_giveback_urb (hcd, urb);
-                local_irq_restore (flags);
-        }
 
+                        spin_unlock(&hcd_root_hub_lock);
+                        usb_hcd_giveback_urb(hcd, urb);
+                        spin_lock(&hcd_root_hub_lock);
+                }
+        }
+        spin_unlock_irqrestore(&hcd_root_hub_lock, flags);
         return 0;
 }