rwsem generic spinlock: use IRQ save/restore spinlocks
Kevin Hilman [Wed, 7 Apr 2010 18:52:46 +0000 (11:52 -0700)]
rwsems can be used with IRQs disabled, particularily in early boot
before IRQs are enabled.  Currently the spin_unlock_irq() usage in the
slow-patch will unconditionally enable interrupts and cause problems
since interrupts are not yet initialized or enabled.

This patch uses save/restore versions of IRQ spinlocks in the slowpath
to ensure interrupts are not unintentionally disabled.

Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/rwsem-spinlock.c

index ccf95bf..ffc9fc7 100644 (file)
@@ -143,13 +143,14 @@ void __sched __down_read(struct rw_semaphore *sem)
 {
        struct rwsem_waiter waiter;
        struct task_struct *tsk;
+       unsigned long flags;
 
-       spin_lock_irq(&sem->wait_lock);
+       spin_lock_irqsave(&sem->wait_lock, flags);
 
        if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
                /* granted */
                sem->activity++;
-               spin_unlock_irq(&sem->wait_lock);
+               spin_unlock_irqrestore(&sem->wait_lock, flags);
                goto out;
        }
 
@@ -164,7 +165,7 @@ void __sched __down_read(struct rw_semaphore *sem)
        list_add_tail(&waiter.list, &sem->wait_list);
 
        /* we don't need to touch the semaphore struct anymore */
-       spin_unlock_irq(&sem->wait_lock);
+       spin_unlock_irqrestore(&sem->wait_lock, flags);
 
        /* wait to be given the lock */
        for (;;) {
@@ -209,13 +210,14 @@ void __sched __down_write_nested(struct rw_semaphore *sem, int subclass)
 {
        struct rwsem_waiter waiter;
        struct task_struct *tsk;
+       unsigned long flags;
 
-       spin_lock_irq(&sem->wait_lock);
+       spin_lock_irqsave(&sem->wait_lock, flags);
 
        if (sem->activity == 0 && list_empty(&sem->wait_list)) {
                /* granted */
                sem->activity = -1;
-               spin_unlock_irq(&sem->wait_lock);
+               spin_unlock_irqrestore(&sem->wait_lock, flags);
                goto out;
        }
 
@@ -230,7 +232,7 @@ void __sched __down_write_nested(struct rw_semaphore *sem, int subclass)
        list_add_tail(&waiter.list, &sem->wait_list);
 
        /* we don't need to touch the semaphore struct anymore */
-       spin_unlock_irq(&sem->wait_lock);
+       spin_unlock_irqrestore(&sem->wait_lock, flags);
 
        /* wait to be given the lock */
        for (;;) {