[PATCH] suspend regression: sysfs deadlock

Suspend deadlocks when trying to unregister /sys/block/sr0.

This comes from Oliver's commit 94bebf4d1b8e7719f0f3944c037a21cfd99a4af7
"Driver core: fix race in sysfs between sysfs_remove_file() and
read()/write()".

sysfs_write_file downs buffer->sem while calling flush_write_buffer, and
flushing that particular write buffer entails downing buffer->sem in
orphan_all_buffers, resulting in the obvious self-deadlock.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/sysfs/inode.c

@@ -227,11 +227,8 @@ static inline void orphan_all_buffers(struct inode *node)
 
 	mutex_lock_nested(&node->i_mutex, I_MUTEX_CHILD);
 	if (node->i_private) {
-		list_for_each_entry(buf, &set->associates, associates) {
-			down(&buf->sem);
+		list_for_each_entry(buf, &set->associates, associates)
 			buf->orphaned = 1;
-			up(&buf->sem);
-		}
 	}
 	mutex_unlock(&node->i_mutex);
 }