fix race that can give duplicate host number

Just once, two fcoe instances got the same host number
from scsi_add_host().

Use atomic_t and atomic_inc_return() to get next host number.
Subtract 1, so that scsi_host still starts with 0.

[jejb: added comment about unusual subtraction]
Signed-off-by: Joe Eykholt <jeykholt@cisco.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index 89d41a424b33..5fd2da494d08 100644
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c
@@ -40,7 +40,7 @@
 #include "scsi_logging.h"
 
 
-static int scsi_host_next_hn;           /* host_no for next new host */
+static atomic_t scsi_host_next_hn;      /* host_no for next new host */
 
 
 static void scsi_host_cls_release(struct device *dev)
@@ -333,7 +333,11 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize)
 
         mutex_init(&shost->scan_mutex);
 
-        shost->host_no = scsi_host_next_hn++; /* XXX(hch): still racy */
+        /*
+         * subtract one because we increment first then return, but we need to
+         * know what the next host number was before increment
+         */
+        shost->host_no = atomic_inc_return(&scsi_host_next_hn) - 1;
         shost->dma_channel = 0xff;
 
         /* These three are default values which can be overridden */