d/freebsd-nq
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

if_free: add a comment explaining why ifindex_free() is performed here

Browse Source
This commit is contained in:
Gleb Smirnoff 2021-11-22 19:53:12 -08:00
parent fe499a8452
commit 3bc40f39fd
1 changed files with 16 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
sys/net/if.c
View File

@ -710,6 +710,22 @@ if_free(struct ifnet *ifp)
ifp->if_flags |= IFF_DYING; /* XXX: Locking */
/*
* XXXGL: An interface index is really an alias to ifp pointer.
* Why would we clear the alias now, and not in the deferred
* context? Indeed there is nothing wrong with some network
* thread obtaining ifp via ifnet_byindex() inside the network
* epoch and then dereferencing ifp while we peform if_free(),
* and after if_free() finished, too.
*
* The reason is the VIMAGE. For some reason it was designed
* to require all sockets drained before destroying, but not all
* ifnets. A vnet destruction calls if_vmove() on ifnet, which
* causes ID change. But ID change and a possible misidentification
* of an ifnet later is a lesser problem, as it doesn't crash kernel.
* A worse problem is that removed interface may outlive the vnet it
* belongs too! The if_free_deferred() would see ifp->if_vnet freed.
*/
CURVNET_SET_QUIET(ifp->if_vnet);
IFNET_WLOCK();
KASSERT(ifp == ifnet_byindex(ifp->if_index),