Author: mav
Date: Thu Oct 19 09:01:15 2017
New Revision: 324752
URL: https://svnweb.freebsd.org/changeset/base/324752
Log:
Relax per-ifnet cif_vrs list double locking in carp(4).
In all cases where cif_vrs list is modified, two locks are held: per-ifnet
CIF_LOCK and global carp_sx. It means to read that list only one of them
is enough to be held, so we can skip CIF_LOCK when we already have carp_sx.
This fixes kernel panic, caused by attempts of copyout() to sleep while
holding non-sleepable CIF_LOCK mutex.
Discussed with: glebius
MFC after: 2 weeks
Sponsored by: iXsystems, Inc.
Modified:
head/sys/netinet/ip_carp.c
Modified: head/sys/netinet/ip_carp.c
==============================================================================
--- head/sys/netinet/ip_carp.c Thu Oct 19 08:17:32 2017 (r324751)
+++ head/sys/netinet/ip_carp.c Thu Oct 19 09:01:15 2017 (r324752)
@@ -175,8 +175,8 @@ static int proto_reg[] = {-1, -1};
* Each softc has a lock sc_mtx. It is used to synchronise carp_input_c(),
* callout-driven events and ioctl()s.
*
- * To traverse the list of softcs on an ifnet we use CIF_LOCK(), to
- * traverse the global list we use the mutex carp_mtx.
+ * To traverse the list of softcs on an ifnet we use CIF_LOCK() or carp_sx.
+ * To traverse the global list we use the mutex carp_mtx.
*
* Known issues with locking:
*
@@ -286,7 +286,8 @@ SYSCTL_VNET_PCPUSTAT(_net_inet_carp, OID_AUTO, stats,
++_i)
#define IFNET_FOREACH_CARP(ifp, sc)
\
- CIF_LOCK_ASSERT(ifp->if_carp); \
+ KASSERT(mtx_owned(&ifp->if_carp->cif_mtx) || \
+ sx_xlocked(&carp_sx), ("cif_vrs not locked")); \
TAILQ_FOREACH((sc), &(ifp)->if_carp->cif_vrs, sc_list)
#define DEMOTE_ADVSKEW(sc) \
@@ -1562,6 +1563,8 @@ carp_alloc(struct ifnet *ifp)
struct carp_softc *sc;
struct carp_if *cif;
+ sx_assert(&carp_sx, SA_XLOCKED);
+
if ((cif = ifp->if_carp) == NULL)
cif = carp_alloc_if(ifp);
@@ -1751,11 +1754,9 @@ carp_ioctl(struct ifreq *ifr, u_long cmd, struct threa
}
if (ifp->if_carp) {
- CIF_LOCK(ifp->if_carp);
IFNET_FOREACH_CARP(ifp, sc)
if (sc->sc_vhid == carpr.carpr_vhid)
break;
- CIF_UNLOCK(ifp->if_carp);
}
if (sc == NULL) {
sc = carp_alloc(ifp);
@@ -1826,11 +1827,9 @@ carp_ioctl(struct ifreq *ifr, u_long cmd, struct threa
priveleged = (priv_check(td, PRIV_NETINET_CARP) == 0);
if (carpr.carpr_vhid != 0) {
- CIF_LOCK(ifp->if_carp);
IFNET_FOREACH_CARP(ifp, sc)
if (sc->sc_vhid == carpr.carpr_vhid)
break;
- CIF_UNLOCK(ifp->if_carp);
if (sc == NULL) {
error = ENOENT;
break;
@@ -1841,7 +1840,6 @@ carp_ioctl(struct ifreq *ifr, u_long cmd, struct threa
int i, count;
count = 0;
- CIF_LOCK(ifp->if_carp);
IFNET_FOREACH_CARP(ifp, sc)
count++;
@@ -1863,7 +1861,6 @@ carp_ioctl(struct ifreq *ifr, u_long cmd, struct threa
}
i++;
}
- CIF_UNLOCK(ifp->if_carp);
}
break;
}
@@ -1918,11 +1915,9 @@ carp_attach(struct ifaddr *ifa, int vhid)
return (ENOPROTOOPT);
}
- CIF_LOCK(cif);
IFNET_FOREACH_CARP(ifp, sc)
if (sc->sc_vhid == vhid)
break;
- CIF_UNLOCK(cif);
if (sc == NULL) {
sx_xunlock(&carp_sx);
return (ENOENT);
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