Date: Sun, 23 Aug 2009 21:00:21 +0000 (UTC) From: Robert Watson <rwatson@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r196482 - head/sys/net Message-ID: <200908232100.n7NL0L1Z072221@svn.freebsd.org>
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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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