linux/net
Alan Stern e041c68341 [PATCH] Notifier chain update: API changes
The kernel's implementation of notifier chains is unsafe.  There is no
protection against entries being added to or removed from a chain while the
chain is in use.  The issues were discussed in this thread:

    http://marc.theaimsgroup.com/?l=linux-kernel&m=113018709002036&w=2

We noticed that notifier chains in the kernel fall into two basic usage
classes:

	"Blocking" chains are always called from a process context
	and the callout routines are allowed to sleep;

	"Atomic" chains can be called from an atomic context and
	the callout routines are not allowed to sleep.

We decided to codify this distinction and make it part of the API.  Therefore
this set of patches introduces three new, parallel APIs: one for blocking
notifiers, one for atomic notifiers, and one for "raw" notifiers (which is
really just the old API under a new name).  New kinds of data structures are
used for the heads of the chains, and new routines are defined for
registration, unregistration, and calling a chain.  The three APIs are
explained in include/linux/notifier.h and their implementation is in
kernel/sys.c.

With atomic and blocking chains, the implementation guarantees that the chain
links will not be corrupted and that chain callers will not get messed up by
entries being added or removed.  For raw chains the implementation provides no
guarantees at all; users of this API must provide their own protections.  (The
idea was that situations may come up where the assumptions of the atomic and
blocking APIs are not appropriate, so it should be possible for users to
handle these things in their own way.)

There are some limitations, which should not be too hard to live with.  For
atomic/blocking chains, registration and unregistration must always be done in
a process context since the chain is protected by a mutex/rwsem.  Also, a
callout routine for a non-raw chain must not try to register or unregister
entries on its own chain.  (This did happen in a couple of places and the code
had to be changed to avoid it.)

Since atomic chains may be called from within an NMI handler, they cannot use
spinlocks for synchronization.  Instead we use RCU.  The overhead falls almost
entirely in the unregister routine, which is okay since unregistration is much
less frequent that calling a chain.

Here is the list of chains that we adjusted and their classifications.  None
of them use the raw API, so for the moment it is only a placeholder.

  ATOMIC CHAINS
  -------------
arch/i386/kernel/traps.c:		i386die_chain
arch/ia64/kernel/traps.c:		ia64die_chain
arch/powerpc/kernel/traps.c:		powerpc_die_chain
arch/sparc64/kernel/traps.c:		sparc64die_chain
arch/x86_64/kernel/traps.c:		die_chain
drivers/char/ipmi/ipmi_si_intf.c:	xaction_notifier_list
kernel/panic.c:				panic_notifier_list
kernel/profile.c:			task_free_notifier
net/bluetooth/hci_core.c:		hci_notifier
net/ipv4/netfilter/ip_conntrack_core.c:	ip_conntrack_chain
net/ipv4/netfilter/ip_conntrack_core.c:	ip_conntrack_expect_chain
net/ipv6/addrconf.c:			inet6addr_chain
net/netfilter/nf_conntrack_core.c:	nf_conntrack_chain
net/netfilter/nf_conntrack_core.c:	nf_conntrack_expect_chain
net/netlink/af_netlink.c:		netlink_chain

  BLOCKING CHAINS
  ---------------
arch/powerpc/platforms/pseries/reconfig.c:	pSeries_reconfig_chain
arch/s390/kernel/process.c:		idle_chain
arch/x86_64/kernel/process.c		idle_notifier
drivers/base/memory.c:			memory_chain
drivers/cpufreq/cpufreq.c		cpufreq_policy_notifier_list
drivers/cpufreq/cpufreq.c		cpufreq_transition_notifier_list
drivers/macintosh/adb.c:		adb_client_list
drivers/macintosh/via-pmu.c		sleep_notifier_list
drivers/macintosh/via-pmu68k.c		sleep_notifier_list
drivers/macintosh/windfarm_core.c	wf_client_list
drivers/usb/core/notify.c		usb_notifier_list
drivers/video/fbmem.c			fb_notifier_list
kernel/cpu.c				cpu_chain
kernel/module.c				module_notify_list
kernel/profile.c			munmap_notifier
kernel/profile.c			task_exit_notifier
kernel/sys.c				reboot_notifier_list
net/core/dev.c				netdev_chain
net/decnet/dn_dev.c:			dnaddr_chain
net/ipv4/devinet.c:			inetaddr_chain

It's possible that some of these classifications are wrong.  If they are,
please let us know or submit a patch to fix them.  Note that any chain that
gets called very frequently should be atomic, because the rwsem read-locking
used for blocking chains is very likely to incur cache misses on SMP systems.
(However, if the chain's callout routines may sleep then the chain cannot be
atomic.)

The patch set was written by Alan Stern and Chandra Seetharaman, incorporating
material written by Keith Owens and suggestions from Paul McKenney and Andrew
Morton.

[jes@sgi.com: restructure the notifier chain initialization macros]
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Signed-off-by: Jes Sorensen <jes@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-03-27 08:44:50 -08:00
..
802 [SNAP]: Remove leftover unused hdr variable 2006-03-20 22:45:37 -08:00
8021q [NET]: Replace skb_pull/skb_postpull_rcsum with skb_pull_rcsum 2006-03-20 22:43:56 -08:00
appletalk [PATCH] capable/capability.h (net/) 2006-01-11 18:42:14 -08:00
atm [NET]: sem2mutex part 2 2006-03-20 22:35:41 -08:00
ax25 [AX.25]: Fix potencial memory hole. 2006-03-19 13:20:06 -08:00
bluetooth [PATCH] Notifier chain update: API changes 2006-03-27 08:44:50 -08:00
bridge [BRIDGE]: Unaligned accesses in the ethernet bridge 2006-03-24 15:44:57 -08:00
core [PATCH] Notifier chain update: API changes 2006-03-27 08:44:50 -08:00
dccp [PATCH] POLLRDHUP/EPOLLRDHUP handling for half-closed devices notifications 2006-03-25 08:22:56 -08:00
decnet [PATCH] Notifier chain update: API changes 2006-03-27 08:44:50 -08:00
econet [ECONET]: Use macro for spinlock_t definition. 2006-01-04 13:56:08 -08:00
ethernet [NET] ethernet: Fix first packet goes out with MAC 00:00:00:00:00:00 2006-02-23 16:18:01 -08:00
ieee80211 [PATCH] Restore channel setting after scan. 2006-03-23 16:18:47 -05:00
ipv4 [PATCH] Notifier chain update: API changes 2006-03-27 08:44:50 -08:00
ipv6 [PATCH] Notifier chain update: API changes 2006-03-27 08:44:50 -08:00
ipx [PATCH] capable/capability.h (net/) 2006-01-11 18:42:14 -08:00
irda [IRDA]: out of range array access 2006-02-09 16:59:48 -08:00
key [NET] sem2mutex: net/ 2006-03-20 22:33:17 -08:00
lapb [NET]: Kill skb->list 2005-08-29 15:31:14 -07:00
llc [LLC]: llc_mac_hdr_init const arguments 2006-03-20 22:59:36 -08:00
netfilter [PATCH] Notifier chain update: API changes 2006-03-27 08:44:50 -08:00
netlink [PATCH] Notifier chain update: API changes 2006-03-27 08:44:50 -08:00
netrom [PATCH] capable/capability.h (net/) 2006-01-11 18:42:14 -08:00
packet [NET]: Fix some whitespace issues in af_packet.c 2006-01-23 16:28:02 -08:00
rose [PATCH] capable/capability.h (net/) 2006-01-11 18:42:14 -08:00
rxrpc [PATCH] fix 'defined but not used' warning in net/rxrpc/main.c::rxrpc_initialise 2006-03-25 08:22:52 -08:00
sched [NET_SCHED]: cls_u32: remove unnecessary NULL-ptr check 2006-03-23 01:16:48 -08:00
sctp Merge master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6 2006-03-25 08:39:20 -08:00
sunrpc [PATCH] knfsd: Tidy up unix_domain_find 2006-03-27 08:44:43 -08:00
tipc [PATCH] s/;;/;/g 2006-03-24 07:33:24 -08:00
unix [PATCH] POLLRDHUP/EPOLLRDHUP handling for half-closed devices notifications 2006-03-25 08:22:56 -08:00
wanrouter [PATCH] capable/capability.h (net/) 2006-01-11 18:42:14 -08:00
x25 [X25]: dte facilities 32 64 ioctl conversion 2006-03-22 00:02:00 -08:00
xfrm [XFRM]: Fix aevent related crash 2006-03-20 22:40:54 -08:00
Kconfig Merge branch 'master' 2006-02-07 01:47:12 -05:00
Makefile [TIPC] Initial merge 2006-01-12 14:06:31 -08:00
TUNABLE Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
compat.c [NET]: socket timestamp 32 bit handler for 64 bit kernel 2006-03-21 23:59:39 -08:00
nonet.c [NET]: Fix sock_init() return value. 2006-01-03 13:11:17 -08:00
socket.c [PATCH] cpuset memory spread: slab cache format 2006-03-24 07:33:23 -08:00
sysctl_net.c [NET]: Fix "sysctl_net.c:36: error: 'core_table' undeclared here" 2005-10-03 14:16:34 -07:00