[patch 4/5] genirq: Move irq resource handling out of spinlocked region

[Thomas Gleixner]

Aside of being conceptually wrong, there is also an actual (hard to
trigger and mostly theoretical) problem.

CPU0                            CPU1
free_irq(X)                     interrupt X
                                spin_lock(desc->lock)
                                wake irq thread()
                                spin_unlock(desc->lock)
spin_lock(desc->lock)
remove action()
shutdown_irq()                  
release_resources()             thread_handler()
spin_unlock(desc->lock)           access released resources.

synchronize_irq()

Move the release resources invocation after synchronize_irq() so it's
guaranteed that the threaded handler has finished.

Move the resource request call out of the desc->lock held region as well,
so the invocation context is the same for both request and release.

This solves the problems with those functions on RT as well.
 
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
---
 kernel/irq/manage.c |   23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1168,6 +1168,14 @@ static int
                new->flags &= ~IRQF_ONESHOT;
 
        mutex_lock(&desc->request_mutex);
+       if (!desc->action) {
+               ret = irq_request_resources(desc);
+               if (ret) {
+                       pr_err("Failed to request resources for %s (irq %d) on 
irqchip %s\n",
+                              new->name, irq, desc->irq_data.chip->name);
+                       goto out_mutex;
+               }
+       }
 
        chip_bus_lock(desc);
 
@@ -1271,13 +1279,6 @@ static int
        }
 
        if (!shared) {
-               ret = irq_request_resources(desc);
-               if (ret) {
-                       pr_err("Failed to request resources for %s (irq %d) on 
irqchip %s\n",
-                              new->name, irq, desc->irq_data.chip->name);
-                       goto out_unlock;
-               }
-
                init_waitqueue_head(&desc->wait_for_threads);
 
                /* Setup the type (level, edge polarity) if configured: */
@@ -1386,6 +1387,10 @@ static int
 
        chip_bus_sync_unlock(desc);
 
+       if (!desc->action)
+               irq_release_resources(desc);
+
+out_mutex:
        mutex_unlock(&desc->request_mutex);
 
 out_thread:
@@ -1484,7 +1489,6 @@ static struct irqaction *__free_irq(unsi
        if (!desc->action) {
                irq_settings_clr_disable_unlazy(desc);
                irq_shutdown(desc);
-               irq_release_resources(desc);
                irq_remove_timings(desc);
        }
 
@@ -1527,6 +1531,9 @@ static struct irqaction *__free_irq(unsi
                }
        }
 
+       if (!desc->action)
+               irq_release_resources(desc);
+
        mutex_unlock(&desc->request_mutex);
 
        irq_chip_pm_put(&desc->irq_data);