Date: Wed, 6 Apr 2011 18:03:49 +0000 (UTC) From: Gleb Smirnoff <glebius@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-8@freebsd.org Subject: svn commit: r220397 - stable/8/sys/net Message-ID: <201104061803.p36I3n9k008491@svn.freebsd.org>
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Author: glebius Date: Wed Apr 6 18:03:49 2011 New Revision: 220397 URL: http://svn.freebsd.org/changeset/base/220397 Log: MFhead 220317: When removing ifnets, we should first remove the reference to ifnet from the interface index, then decrease refcount, not vice versa. Otherwise there is a race (reproducible) when if_free_internal() contests on IFNET_WLOCK(), and we got a zero-refed ifnet in the index for a long time. It may be picked by some other thread, that runs ifnet_byindex_ref(), who takes the ifnet from index, and bumps refcount. When reader drops the lock, if_free_internal() proceeds with free. Then reader tries to free it a second time. Modified: stable/8/sys/net/if.c Directory Properties: stable/8/sys/ (props changed) stable/8/sys/amd64/include/xen/ (props changed) stable/8/sys/cddl/contrib/opensolaris/ (props changed) stable/8/sys/contrib/dev/acpica/ (props changed) stable/8/sys/contrib/pf/ (props changed) Modified: stable/8/sys/net/if.c ============================================================================== --- stable/8/sys/net/if.c Wed Apr 6 18:00:26 2011 (r220396) +++ stable/8/sys/net/if.c Wed Apr 6 18:03:49 2011 (r220397) @@ -484,8 +484,8 @@ if_alloc(u_char type) } /* - * Do the actual work of freeing a struct ifnet, associated index, and layer - * 2 common structure. This call is made when the last reference to an + * Do the actual work of freeing a struct ifnet, and layer 2 common + * structure. This call is made when the last reference to an * interface is released. */ static void @@ -495,13 +495,6 @@ if_free_internal(struct ifnet *ifp) KASSERT((ifp->if_flags & IFF_DYING), ("if_free_internal: interface not dying")); - IFNET_WLOCK(); - KASSERT(ifp == ifnet_byindex_locked(ifp->if_index), - ("%s: freeing unallocated ifnet", ifp->if_xname)); - - ifindex_free_locked(ifp->if_index); - IFNET_WUNLOCK(); - if (if_com_free[ifp->if_alloctype] != NULL) if_com_free[ifp->if_alloctype](ifp->if_l2com, ifp->if_alloctype); @@ -532,6 +525,14 @@ if_free_type(struct ifnet *ifp, u_char t ifp->if_alloctype)); ifp->if_flags |= IFF_DYING; /* XXX: Locking */ + + IFNET_WLOCK(); + KASSERT(ifp == ifnet_byindex_locked(ifp->if_index), + ("%s: freeing unallocated ifnet", ifp->if_xname)); + + ifindex_free_locked(ifp->if_index); + IFNET_WUNLOCK(); + if (!refcount_release(&ifp->if_refcount)) return; if_free_internal(ifp);
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