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Commit 7e43f112 authored by David S. Miller's avatar David S. Miller
Browse files

pkt_sched: Make sure RTNL is held in qdisc_root_lock(). 



It is the only legal environment in which this can be
used.

Add some commentary explaining the situation.

Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 35ed4e75

include/net/sch_generic.h

+12 −0
Original line number Diff line number Diff line
@@ -193,10 +193,22 @@ static inline struct Qdisc *qdisc_root(struct Qdisc *qdisc) 
	return qdisc->dev_queue->qdisc;

}



/* The qdisc root lock is a mechanism by which to top level

 * of a qdisc tree can be locked from any qdisc node in the

 * forest.  This allows changing the configuration of some

 * aspect of the qdisc tree while blocking out asynchronous

 * qdisc access in the packet processing paths.

 *

 * It is only legal to do this when the root will not change

 * on us.  Otherwise we'll potentially lock the wrong qdisc

 * root.  This is enforced by holding the RTNL semaphore, which

 * all users of this lock accessor must do.

 */

static inline spinlock_t *qdisc_root_lock(struct Qdisc *qdisc)

{

	struct Qdisc *root = qdisc_root(qdisc);



	ASSERT_RTNL();

	return qdisc_lock(root);

}