__scsi_remove_device() in scsi_forget_host() is executed out of scan_mutex

and races with scsi_destroy_sdev() <- scsi_sysfs_add_devices() <-
scsi_finish_async_scan().  The result is use after free and/or double
free, oops.

The fix is simple, move scsi_forget_host() under scan_mutex.

scsi_forget_host() is just sequence of __scsi_remove_device().  All
another calls of __scsi_remove_device() are made under scan_mutex.  So
that it is safe.
Signed-off-by: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/scsi/hosts.c

@@ -164,8 +164,8 @@ void scsi_remove_host(struct Scsi_Host *shost)
 			return;
 		}
 	spin_unlock_irqrestore(shost->host_lock, flags);
-	mutex_unlock(&shost->scan_mutex);
 	scsi_forget_host(shost);
+	mutex_unlock(&shost->scan_mutex);
 	scsi_proc_host_rm(shost);
 
 	spin_lock_irqsave(shost->host_lock, flags);