libata: Fix a potential race condition in ata_scsi_park_show()

Peter Moulder has pointed out that there is a slight chance that a
negative value might be passed to jiffies_to_msecs() in
ata_scsi_park_show(). This is fixed by saving the value of jiffies in a
local variable, thus also reducing code since the volatile variable
jiffies is accessed only once.

Signed-off-by: Elias Oltmanns <eo@nebensachen.de>
Signed-off-by: Tejun Heo <tj.kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index bbb30d882f05..3fa75eac135d 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -190,7 +190,7 @@ static ssize_t ata_scsi_park_show(struct device *device,
         struct ata_port *ap;
         struct ata_link *link;
         struct ata_device *dev;
-        unsigned long flags;
+        unsigned long flags, now;
         unsigned int uninitialized_var(msecs);
         int rc = 0;
 
@@ -208,10 +208,11 @@ static ssize_t ata_scsi_park_show(struct device *device,
         }
 
         link = dev->link;
+        now = jiffies;
         if (ap->pflags & ATA_PFLAG_EH_IN_PROGRESS &&
             link->eh_context.unloaded_mask & (1 << dev->devno) &&
-            time_after(dev->unpark_deadline, jiffies))
-                msecs = jiffies_to_msecs(dev->unpark_deadline - jiffies);
+            time_after(dev->unpark_deadline, now))
+                msecs = jiffies_to_msecs(dev->unpark_deadline - now);
         else
                 msecs = 0;