bql: Avoid possible inconsistent calculation.
Hiroaki SHIMODA [Wed, 30 May 2012 12:25:37 +0000 (12:25 +0000)]
[ 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@gmail.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Denys Fedoryshchenko <denys@visp.net.lb>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

lib/dynamic_queue_limits.c

index 0fafa77..0777c5a 100644 (file)
 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, unsigned int count)
        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);