Author: rwatson
Date: Sun Aug 23 21:00:21 2009
New Revision: 196482
URL: http://svn.freebsd.org/changeset/base/196482
Log:
Rather than using IFNET_RLOCK() when iterating over (and modifying) the
ifnet list during if_ef load, directly acquire the ifnet_sxlock
exclusively. That way when if_alloc() recurses the lock, it's a write
recursion rather than a read->write recursion.
This code structure is arguably a bug, so add a comment indicating that
this is the case. Post-8.0, we should fix this, but this commit
resolves panic-on-load for if_ef.
Discussed with: bz, julian
Reported by: phk
MFC after: 3 days
Modified:
head/sys/net/if_ef.c
Modified: head/sys/net/if_ef.c
==============================================================================
--- head/sys/net/if_ef.c Sun Aug 23 20:40:19 2009 (r196481)
+++ head/sys/net/if_ef.c Sun Aug 23 21:00:21 2009 (r196482)
@@ -492,7 +492,20 @@ ef_load(void)
VNET_LIST_RLOCK();
VNET_FOREACH(vnet_iter) {
CURVNET_SET(vnet_iter);
- IFNET_RLOCK();
+
+ /*
+ * XXXRW: The following loop walks the ifnet list while
+ * modifying it, something not well-supported by ifnet
+ * locking. To avoid lock upgrade/recursion issues, manually
+ * acquire a write lock of ifnet_sxlock here, rather than a
+ * read lock, so that when if_alloc() recurses the lock, we
+ * don't panic. This structure, in which if_ef automatically
+ * attaches to all ethernet interfaces, should be replaced
+ * with a model like that found in if_vlan, in which
+ * interfaces are explicitly configured, which would avoid
+ * this (and other) problems.
+ */
+ sx_xlock(&ifnet_sxlock);
TAILQ_FOREACH(ifp, &V_ifnet, if_link) {
if (ifp->if_type != IFT_ETHER) continue;
EFDEBUG("Found interface %s\n", ifp->if_xname);
@@ -523,7 +536,7 @@ ef_load(void)
efcount++;
SLIST_INSERT_HEAD(&efdev, efl, el_next);
}
- IFNET_RUNLOCK();
+ sx_xunlock(&ifnet_sxlock);
CURVNET_RESTORE();
}
VNET_LIST_RUNLOCK();
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