[ 018/187] bql: Avoid possible inconsistent calculation.

[Greg Kroah-Hartman]

From: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------


From: Hiroaki SHIMODA <shimoda.hiroaki@xxxxxxxxx>

[ Upstream commit 914bec1011a25f65cdc94988a6f974bfb9a3c10d ]

dql->num_queued could change while processing dql_completed().
To provide consistent calculation, added an on stack variable.

Signed-off-by: Hiroaki SHIMODA <shimoda.hiroaki@xxxxxxxxx>
Cc: Tom Herbert <therbert@xxxxxxxxxx>
Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Cc: Denys Fedoryshchenko <denys@xxxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 lib/dynamic_queue_limits.c |   12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

--- a/lib/dynamic_queue_limits.c
+++ b/lib/dynamic_queue_limits.c
@@ -17,16 +17,18 @@
 void dql_completed(struct dql *dql, unsigned int count)
 {
 	unsigned int inprogress, prev_inprogress, limit;
-	unsigned int ovlimit, completed;
+	unsigned int ovlimit, completed, num_queued;
 	bool all_prev_completed;
 
+	num_queued = ACCESS_ONCE(dql->num_queued);
+
 	/* Can't complete more than what's in queue */
-	BUG_ON(count > dql->num_queued - dql->num_completed);
+	BUG_ON(count > num_queued - dql->num_completed);
 
 	completed = dql->num_completed + count;
 	limit = dql->limit;
-	ovlimit = POSDIFF(dql->num_queued - dql->num_completed, limit);
-	inprogress = dql->num_queued - completed;
+	ovlimit = POSDIFF(num_queued - dql->num_completed, limit);
+	inprogress = num_queued - completed;
 	prev_inprogress = dql->prev_num_queued - dql->num_completed;
 	all_prev_completed = AFTER_EQ(completed, dql->prev_num_queued);
 
@@ -106,7 +108,7 @@ void dql_completed(struct dql *dql, unsi
 	dql->prev_ovlimit = ovlimit;
 	dql->prev_last_obj_cnt = dql->last_obj_cnt;
 	dql->num_completed = completed;
-	dql->prev_num_queued = dql->num_queued;
+	dql->prev_num_queued = num_queued;
 }
 EXPORT_SYMBOL(dql_completed);
 


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