sysfs: Allow sysfs_notify_dirent to be called from interrupt context.

sysfs_notify_dirent is a simple atomic operation that can be used to
alert user-space that new data can be read from a sysfs attribute.

Unfortunately it cannot currently be called from non-process context
because of its use of spin_lock which is sometimes taken with
interrupts enabled.

So change all lockers of sysfs_open_dirent_lock to disable interrupts,
thus making sysfs_notify_dirent safe to be called from non-process
context (as drivers/md does in md_safemode_timeout).

sysfs_get_open_dirent is (documented as being) only called from
process context, so it uses spin_lock_irq.  Other places
use spin_lock_irqsave.

The usage for sysfs_notify_dirent in md_safemode_timeout was
introduced in 2.6.28, so this patch is suitable for that and more
recent kernels.
Reported-by: Joel Andres Granados <jgranado@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

fs/sysfs/file.c

@@ -268,7 +268,7 @@ static int sysfs_get_open_dirent(struct sysfs_dirent *sd,
 	struct sysfs_open_dirent *od, *new_od = NULL;
 
  retry:
-	spin_lock(&sysfs_open_dirent_lock);
+	spin_lock_irq(&sysfs_open_dirent_lock);
 
 	if (!sd->s_attr.open && new_od) {
 		sd->s_attr.open = new_od;
@@ -281,7 +281,7 @@ static int sysfs_get_open_dirent(struct sysfs_dirent *sd,
 		list_add_tail(&buffer->list, &od->buffers);
 	}
 
-	spin_unlock(&sysfs_open_dirent_lock);
+	spin_unlock_irq(&sysfs_open_dirent_lock);
 
 	if (od) {
 		kfree(new_od);
@@ -315,8 +315,9 @@ static void sysfs_put_open_dirent(struct sysfs_dirent *sd,
 				  struct sysfs_buffer *buffer)
 {
 	struct sysfs_open_dirent *od = sd->s_attr.open;
+	unsigned long flags;
 
-	spin_lock(&sysfs_open_dirent_lock);
+	spin_lock_irqsave(&sysfs_open_dirent_lock, flags);
 
 	list_del(&buffer->list);
 	if (atomic_dec_and_test(&od->refcnt))
@@ -324,7 +325,7 @@ static void sysfs_put_open_dirent(struct sysfs_dirent *sd,
 	else
 		od = NULL;
 
-	spin_unlock(&sysfs_open_dirent_lock);
+	spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags);
 
 	kfree(od);
 }
@@ -456,8 +457,9 @@ static unsigned int sysfs_poll(struct file *filp, poll_table *wait)
 void sysfs_notify_dirent(struct sysfs_dirent *sd)
 {
 	struct sysfs_open_dirent *od;
+	unsigned long flags;
 
-	spin_lock(&sysfs_open_dirent_lock);
+	spin_lock_irqsave(&sysfs_open_dirent_lock, flags);
 
 	od = sd->s_attr.open;
 	if (od) {
@@ -465,7 +467,7 @@ void sysfs_notify_dirent(struct sysfs_dirent *sd)
 		wake_up_interruptible(&od->poll);
 	}
 
-	spin_unlock(&sysfs_open_dirent_lock);
+	spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags);
 }
 EXPORT_SYMBOL_GPL(sysfs_notify_dirent);