Hi, On Tue, Aug 16, 2005 at 07:01:57PM -0700, Paul E. McKenney wrote: > On Tue, Aug 16, 2005 at 05:09:29PM -0700, Suzanne Wood wrote: > [ . . . ] > > A read-side critical section is marked to protect the dereference of the > > dn_ptr and assignment to dn_db which is a pointer to a dn_dev. (struct > > net_device is defined in /linux/netdevice.h and its dn_ptr in > > /include/net/dn_dev.h) Should this rcu-protection be extended to the line > > following rcu_read_lock()? Even though use_long is a simple char, it > > appears to be a member of an rcu-protected structure. > > Looks to me that this could indeed be a problem -- the structure > pointed to by dn_db could potentially be freed immediately after the > rcu_read_unlock(), unless there is some other non-obvious locking > mechanism protecting it. In which case, why the rcu_read_lock() > and rcu_read_unlock()... > > Thanx, Paul
The dev->dn_ptr points to the DECnet specific portion of a net device which is allocated in dn_dev.c/dn_dev_up and freed in dn_dev.c/dn_dev_delete when the net device goes up and down. So I think you are right in that as far as I can see, its possible for a net device going down to race with this, but the window of opportunity is very small indeed (in fact possibly zero?) due to the ordering of operations in dn_dev_delete where dev->dn_ptr is set to NULL (esentially preventing any more DECnet packets being received on that device) before flushing all neighbours and only then releasing dn_db. Also, Patrick Caulfield is maintaining this code now, so I've added him to the CC list. Thanks for the report though, Steve. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
