memstick: avert possible race condition between idr_pre_get and idr_get_new

Implement the usual pattern around idr_pre_get() and idr_get_new() to
handlethe situation where another thread concurrently steals this thread's
idr_pre_get() preallocation.
Signed-off-by: Alex Dubov <oakad@yahoo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/memstick/core/memstick.c

@@ -511,14 +511,18 @@ int memstick_add_host(struct memstick_host *host)
 {
 	int rc;
 
+	while (1) {
 		if (!idr_pre_get(&memstick_host_idr, GFP_KERNEL))
 			return -ENOMEM;
 
 		spin_lock(&memstick_host_lock);
 		rc = idr_get_new(&memstick_host_idr, host, &host->id);
 		spin_unlock(&memstick_host_lock);
-	if (rc)
+		if (!rc)
+			break;
+		else if (rc != -EAGAIN)
 			return rc;
+	}
 
 	dev_set_name(&host->dev, "memstick%u", host->id);
 

drivers/memstick/core/mspro_block.c

@@ -1206,10 +1206,12 @@ static int mspro_block_init_disk(struct memstick_dev *card)
 
 	msb->page_size = be16_to_cpu(sys_info->unit_size);
 
-	if (!idr_pre_get(&mspro_block_disk_idr, GFP_KERNEL))
+	mutex_lock(&mspro_block_disk_lock);
+	if (!idr_pre_get(&mspro_block_disk_idr, GFP_KERNEL)) {
+		mutex_unlock(&mspro_block_disk_lock);
 		return -ENOMEM;
+	}
 
-	mutex_lock(&mspro_block_disk_lock);
 	rc = idr_get_new(&mspro_block_disk_idr, card, &disk_id);
 	mutex_unlock(&mspro_block_disk_lock);