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

Add some commentary explaining the situation.
Signed-off-by: default avatarDavid S. Miller <>
parent 35ed4e75
......@@ -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);
return qdisc_lock(root);
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