rwsem generic spinlock: use IRQ save/restore spinlocks

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>

1 files changed, 8 insertions, 6 deletions

diff --git a/lib/rwsem-spinlock.c b/lib/rwsem-spinlock.c
index ccf95bff7984..ffc9fc7f3b05 100644
--- a/lib/rwsem-spinlock.c
+++ b/lib/rwsem-spinlock.c
@@ -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 (;;) {