Re: pmf_register_irq_client gives sleep with locks held warning

[Johannes Berg <johannes@sipsolutions.net>]

On Thu, 2006-06-01 at 10:59 +1000, Benjamin Herrenschmidt wrote:

> This fixes request_irq() potentially called from atomic context.
> [...]

Sorry, almost forgot about this.

I don't think your patch is right, it seems to me that now
pmf_unregister_irq_client races against pmf_do_irq: what happens when an
interrupt comes in right in the middle of the list_del()?

It might actually not do any harm due to the way list_del() and
pmf_do_irq() work and the fact that client->handler() must still be
prepared to be called... But I'd rather make it explicit.

By the way, what do I do when like this I change a patch? Do I rely on
your Signed-off-by and simply put mine instead (like I did now)?

Anyway, here's a changed patch that illustrates my point. I've tested it
and it works and as expected fixes the problem :)
---
This fixes request_irq() being called with interrupts disabled in the
powermac platform function code when registering the first irq client
for a given platform function.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>

--- a/arch/powerpc/platforms/powermac/pfunc_core.c
+++ b/arch/powerpc/platforms/powermac/pfunc_core.c
@@ -11,6 +11,7 @@ #include <linux/delay.h>
 #include <linux/kernel.h>
 #include <linux/spinlock.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 
 #include <asm/semaphore.h>
 #include <asm/prom.h>
@@ -546,6 +547,7 @@ struct pmf_device {
 
 static LIST_HEAD(pmf_devices);
 static spinlock_t pmf_lock = SPIN_LOCK_UNLOCKED;
+static DEFINE_MUTEX(pmf_irq_mutex);
 
 static void pmf_release_device(struct kref *kref)
 {
@@ -864,16 +866,25 @@ int pmf_register_irq_client(struct devic
 
 	spin_lock_irqsave(&pmf_lock, flags);
 	func = __pmf_find_function(target, name, PMF_FLAGS_INT_GEN);
-	if (func == NULL) {
-		spin_unlock_irqrestore(&pmf_lock, flags);
+	if (func)
+		func = pmf_get_function(func);
+	spin_unlock_irqrestore(&pmf_lock, flags);
+	if (func == NULL)
 		return -ENODEV;
-	}
+
+	/* guard against manipulations of list */
+	mutex_lock(&pmf_irq_mutex);
 	if (list_empty(&func->irq_clients))
 		func->dev->handlers->irq_enable(func);
+
+	/* guard against pmf_do_irq while changing list */
+	spin_lock_irqsave(&pmf_lock, flags);
 	list_add(&client->link, &func->irq_clients);
-	client->func = func;
 	spin_unlock_irqrestore(&pmf_lock, flags);
 
+	client->func = func;
+	mutex_unlock(&pmf_irq_mutex);
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(pmf_register_irq_client);
@@ -885,12 +896,19 @@ void pmf_unregister_irq_client(struct pm
 
 	BUG_ON(func == NULL);
 
-	spin_lock_irqsave(&pmf_lock, flags);
+	/* guard against manipulations of list */
+	mutex_lock(&pmf_irq_mutex);
 	client->func = NULL;
+
+	/* guard against pmf_do_irq while changing list */
+	spin_lock_irqsave(&pmf_lock, flags);
 	list_del(&client->link);
+	spin_unlock_irqrestore(&pmf_lock, flags);
+
 	if (list_empty(&func->irq_clients))
 		func->dev->handlers->irq_disable(func);
-	spin_unlock_irqrestore(&pmf_lock, flags);
+	mutex_unlock(&pmf_irq_mutex);
+	pmf_put_function(func);
 }
 EXPORT_SYMBOL_GPL(pmf_unregister_irq_client);