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Date: Tue, 1 Apr 2008 23:45:22 +0200
From: Rodolfo Giometti <giometti@...eenne.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, dwmw2@...radead.org,
davej@...hat.com, sam@...nborg.org, greg@...ah.com,
randy.dunlap@...cle.com
Subject: Re: [PATCH 1/7] LinuxPPS core support.
On Tue, Apr 01, 2008 at 01:55:55AM -0700, Andrew Morton wrote:
>
> This can all be handled with suitable locking and refcounting. The device
> which is delivering PPS interrupts has a reference on the PPS data
> structures. If userspace has PPS open then it also has a reference.
>
> The thread of control which releases the last reference to the PPS data
> structures also frees them all up. This may require a schedule_work() if
> we need to support release-from-interrupt (as it appears that we do), but
> that's OK - we just need to be able to make the PPS data structures
> ineligible for new lookups while the schedule_work() is pending.
>
> There should be no need for any thread of control to wait for any other thread
> of control to do anything. Get the refcounting right and everything
> can be done synchronously.
Here my solution by using get/put functions:
diff --git a/drivers/pps/kapi.c b/drivers/pps/kapi.c
index d75c8c8..61c1569 100644
--- a/drivers/pps/kapi.c
+++ b/drivers/pps/kapi.c
@@ -59,6 +59,62 @@ static void pps_add_offset(struct pps_ktime *ts, struct pps_ktime *offset)
* Exported functions
*/
+/* pps_get_source - find a PPS source
+ *
+ * source: the PPS source ID.
+ *
+ * This function is used to find an already registered PPS source into the
+ * system.
+ *
+ * The function returns NULL if found nothing, otherwise it returns a pointer
+ * to the PPS source data struct (the refcounter is incremented by 1).
+ */
+
+struct pps_device *pps_get_source(int source)
+{
+ struct pps_device *pps;
+ unsigned long flags;
+
+ spin_lock_irqsave(&pps_idr_lock, flags);
+
+ pps = idr_find(&pps_idr, source);
+ if (pps != NULL)
+ atomic_inc(&pps->usage);
+
+ spin_unlock_irqrestore(&pps_idr_lock, flags);
+
+ return pps;
+}
+
+/* pps_put_source - free the PPS source data
+ *
+ * pps: a pointer to the PPS source.
+ *
+ * This function is used to free a PPS data struct if its refcount is 0.
+ */
+
+void pps_put_source(struct pps_device *pps)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&pps_idr_lock, flags);
+
+ BUG_ON(atomic_read(&pps->usage) == 0);
+
+ if (!atomic_dec_and_test(&pps->usage))
+ goto exit;
+
+ /* No more reference to the PPS source. We can safely remove the
+ * PPS data struct.
+ */
+ idr_remove(&pps_idr, pps->id);
+
+ kfree(pps);
+
+exit:
+ spin_unlock_irqrestore(&pps_idr_lock, flags);
+}
+
/* pps_register_source - add a PPS source in the system
*
* info: the PPS info struct
@@ -133,8 +189,7 @@ int pps_register_source(struct pps_source_info *info, int default_params)
init_waitqueue_head(&pps->queue);
spin_lock_init(&pps->lock);
- atomic_set(&pps->usage, 0);
- init_waitqueue_head(&pps->usage_queue);
+ atomic_set(&pps->usage, 1);
/* Create the char device */
err = pps_register_cdev(pps);
@@ -179,21 +234,14 @@ void pps_unregister_source(int source)
pps = idr_find(&pps_idr, source);
if (!pps) {
+ BUG();
spin_unlock_irq(&pps_idr_lock);
return;
}
-
- /* This should be done first in order to deny IRQ handlers
- * to access PPS structs
- */
-
- idr_remove(&pps_idr, pps->id);
spin_unlock_irq(&pps_idr_lock);
- wait_event(pps->usage_queue, atomic_read(&pps->usage) == 0);
-
pps_unregister_cdev(pps);
- kfree(pps);
+ pps_put_source(pps);
}
EXPORT_SYMBOL(pps_unregister_source);
@@ -231,16 +279,7 @@ void pps_event(int source, int event, void *data)
return;
}
- spin_lock_irqsave(&pps_idr_lock, flags);
- pps = idr_find(&pps_idr, source);
-
- /* If we find a valid PPS source we lock it before leaving
- * the lock!
- */
- if (pps)
- atomic_inc(&pps->usage);
- spin_unlock_irqrestore(&pps_idr_lock, flags);
-
+ pps = pps_get_source(source);
if (!pps)
return;
@@ -286,9 +325,6 @@ void pps_event(int source, int event, void *data)
spin_unlock_irqrestore(&pps->lock, flags);
/* Now we can release the PPS source for (possible) deregistration */
- spin_lock_irqsave(&pps_idr_lock, flags);
- atomic_dec(&pps->usage);
- wake_up_all(&pps->usage_queue);
- spin_unlock_irqrestore(&pps_idr_lock, flags);
+ pps_put_source(pps);
}
EXPORT_SYMBOL(pps_event);
diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c
index 5cbfeb9..a46f8f4 100644
--- a/drivers/pps/pps.c
+++ b/drivers/pps/pps.c
@@ -214,15 +214,7 @@ static int pps_cdev_open(struct inode *inode, struct file *file)
struct pps_device, cdev);
int found;
- spin_lock_irq(&pps_idr_lock);
- found = idr_find(&pps_idr, pps->id) != NULL;
-
- /* Lock the PPS source against (possible) deregistration */
- if (found)
- atomic_inc(&pps->usage);
-
- spin_unlock_irq(&pps_idr_lock);
-
+ found = pps_get_source(pps->id) != 0;
if (!found)
return -ENODEV;
@@ -236,8 +228,7 @@ static int pps_cdev_release(struct inode *inode, struct file *file)
struct pps_device *pps = file->private_data;
/* Free the PPS source and wake up (possible) deregistration */
- atomic_dec(&pps->usage);
- wake_up_all(&pps->usage_queue);
+ pps_put_source(pps);
return 0;
}
diff --git a/include/linux/pps.h b/include/linux/pps.h
index aca0e77..e23aaa6 100644
--- a/include/linux/pps.h
+++ b/include/linux/pps.h
@@ -173,7 +173,6 @@ struct pps_device {
spinlock_t lock;
atomic_t usage; /* usage count */
- wait_queue_head_t usage_queue;
};
/*
@@ -189,6 +188,8 @@ extern struct device_attribute pps_attrs[];
* Exported functions
*/
+struct pps_device *pps_get_source(int source);
+extern void pps_put_source(struct pps_device *pps);
extern int pps_register_source(struct pps_source_info *info,
int default_params);
extern void pps_unregister_source(int source);
I'll send a new patchset ASAP!
Rodolfo
--
GNU/Linux Solutions e-mail: giometti@...eenne.com
Linux Device Driver giometti@...dd.com
Embedded Systems giometti@...ux.it
UNIX programming phone: +39 349 2432127
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