interface is configured. A callback function uses VLAN_ATTACHED() function
which check ec->ec_nvlans, the value should be incremented before calling the
callback. This bug was added in if_vlan.c rev. 1.83 (2015/11/19).
The data can be accessed from sysctl, ioctl, interface watchdog
(if_slowtimo) and interrupt handlers. We need to protect the data against
parallel accesses from them.
Currently the mutex is applied to some drivers, we need to apply it to all
drivers in the future.
Note that the mutex is adaptive one for ease of implementation but some
drivers access the data in interrupt context so we cannot apply the mutex
to every drivers as is. We have two options: one is to replace the mutex
with a spin one, which requires some additional works (see
ether_multicast_sysctl), and the other is to modify the drivers to access
the data not in interrupt context somehow.
carp_clone_destroy calls ether_ifdetach so not calling ether_ifattach is
inconsistent. If we add something pair of initialization and destruction
to ether_ifattach and ether_ifdetach (e.g., mutex_init/mutex_destroy),
ether_ifdetach of carp_clone_destroy won't work. So use ether_ifattach.
In order to do so, make ether_ifattach accept the 2nd argument (lla) as
NULL to allow carp to initialize its link level address by itself.
It's useless in this case, because without it we can know that
the lock is held or not on a next lock acquisition and even more
if LOCKDEBUG is enabled a failure on the acquisition will provide
useful information for debugging while an assertion failure will
provide just the fact that the assertion failed.
llentry timer (of nd6) holds both llentry's lock and softnet_lock.
A caller also holds them and calls callout_halt to wait for the
timer to quit. However we can pass only one lock to callout_halt,
so passing either of them can cause a deadlock. Fix it by avoid
calling callout_halt without holding llentry's lock.
BTW in the first place we cannot pass llentry's lock to callout_halt
because it's a rwlock...
The benefits of the change are:
- We can reduce codes
- We can provide the same behavior between drivers
- Where/When if_ipackets is counted up
- Note that some drivers still update packet statistics in their own
way (periodical update)
- Moved bpf_mtap run in softint
- This makes it easy to MP-ify bpf
Proposed on tech-kern and tech-net
See the following descriptions for details.
Proposed on tech-kern and tech-net
Overview
--------
We protect the routing table with a rwock and protect
rtcaches with another rwlock. Each rtentry is protected
from being freed or updated via reference counting and psref.
Global rwlocks
--------------
There are two rwlocks; one for the routing table (rt_lock) and
the other for rtcaches (rtcache_lock). rtcache_lock covers
all existing rtcaches; there may have room for optimizations
(future work).
The locking order is rtcache_lock first and rt_lock is next.
rtentry references
------------------
References to an rtentry is managed with reference counting
and psref. Either of the two mechanisms is used depending on
where a rtentry is obtained. Reference counting is used when
we obtain a rtentry from the routing table directly via
rtalloc1 and rtrequest{,1} while psref is used when we obtain
a rtentry from a rtcache via rtcache_* APIs. In both cases,
a caller can sleep/block with holding an obtained rtentry.
The reasons why we use two different mechanisms are (i) only
using reference counting hurts the performance due to atomic
instructions (rtcache case) (ii) ease of implementation;
applying psref to APIs such rtaloc1 and rtrequest{,1} requires
additional works (adding a local variable and an argument).
We will finally migrate to use only psref but we can do it
when we have a lockless routing table alternative.
Reference counting for rtentry
------------------------------
rt_refcnt now doesn't count permanent references such as for
rt_timers and rtcaches, instead it is used only for temporal
references when obtaining a rtentry via rtalloc1 and rtrequest{,1}.
We can do so because destroying a rtentry always involves
removing references of rt_timers and rtcaches to the rtentry
and we don't need to track such references. This also makes
it easy to wait for readers to release references on deleting
or updating a rtentry, i.e., we can simply wait until the
reference counter is 0 or 1. (If there are permanent references
the counter can be arbitrary.)
rt_ref increments a reference counter of a rtentry and rt_unref
decrements it. rt_ref is called inside APIs (rtalloc1 and
rtrequest{,1} so users don't need to care about it while
users must call rt_unref to an obtained rtentry after using it.
rtfree is removed and we use rt_unref and rt_free instead.
rt_unref now just decrements the counter of a given rtentry
and rt_free just tries to destroy a given rtentry.
See the next section for destructions of rtentries by rt_free.
Destructions of rtentries
-------------------------
We destroy a rtentry only when we call rtrequst{,1}(RTM_DELETE);
the original implementation can destroy in any rtfree where it's
the last reference. If we use reference counting or psref, it's
easy to understand if the place that a rtentry is destroyed is
fixed.
rt_free waits for references to a given rtentry to be released
before actually destroying the rtentry. rt_free uses a condition
variable (cv_wait) (and psref_target_destroy for psref) to wait.
Unfortunately rtrequst{,1}(RTM_DELETE) can be called in softint
that we cannot use cv_wait. In that case, we have to defer the
destruction to a workqueue.
rtentry#rt_cv, rtentry#rt_psref and global variables
(see rt_free_global) are added to conduct the procedure.
Updates of rtentries
--------------------
One difficulty to use refcnt/psref instead of rwlock for rtentry
is updates of rtentries. We need an additional mechanism to
prevent readers from seeing inconsistency of a rtentry being
updated.
We introduce RTF_UPDATING flag to rtentries that are updating.
While the flag is set to a rtentry, users cannot acquire the
rtentry. By doing so, we avoid users to see inconsistent
rtentries.
There are two options when a user tries to acquire a rtentry
with the RTF_UPDATING flag; if a user runs in softint context
the user fails to acquire a rtentry (NULL is returned).
Otherwise a user waits until the update completes by waiting
on cv.
The procedure of a updater is simpler to destruction of
a rtentry. Wait on cv (and psref) and after all readers left,
proceed with the update.
Global variables (see rt_update_global) are added to conduct
the procedure.
Currently we apply the mechanism to only RTM_CHANGE in
rtsock.c. We would have to apply other codes. See
"Known issues" section.
psref for rtentry
-----------------
When we obtain a rtentry from a rtcache via rtcache_* APIs,
psref is used to reference to the rtentry.
rtcache_ref acquires a reference to a rtentry with psref
and rtcache_unref releases the reference after using it.
rtcache_ref is called inside rtcache_* APIs and users don't
need to take care of it while users must call rtcache_unref
to release the reference.
struct psref and int bound that is needed for psref is
embedded into struct route. By doing so we don't need to
add local variables and additional argument to APIs.
However this adds another constraint to psref other than
reference counting one's; holding a reference of an rtentry
via a rtcache is allowed by just one caller at the same time.
So we must not acquire a rtentry via a rtcache twice and
avoid a recursive use of a rtcache. And also a rtcache must
be arranged to be used by a LWP/softint at the same time
somehow. For IP forwarding case, we have per-CPU rtcaches
used in softint so the constraint is guaranteed. For a h
rtcache of a PCB case, the constraint is guaranteed by the
solock of each PCB. Any other cases (pf, ipf, stf and ipsec)
are currently guaranteed by only the existence of the global
locks (softnet_lock and/or KERNEL_LOCK). If we've found the
cases that we cannot guarantee the constraint, we would need
to introduce other rtcache APIs that use simple reference
counting.
psref of rtcache is created with IPL_SOFTNET and so rtcache
shouldn't used at an IPL higher than IPL_SOFTNET.
Note that rtcache_free is used to invalidate a given rtcache.
We don't need another care by my change; just keep them as
they are.
Performance impact
------------------
When NET_MPSAFE is disabled the performance drop is 3% while
when it's enabled the drop is increased to 11%. The difference
comes from that currently we don't take any global locks and
don't use psref if NET_MPSAFE is disabled.
We can optimize the performance of the case of NET_MPSAFE
on by reducing lookups of rtcache that uses psref;
currently we do two lookups but we should be able to trim
one of two. This is a future work.
Known issues
------------
There are two known issues to be solved; one is that
a caller of rtrequest(RTM_ADD) may change rtentry (see rtinit).
We need to prevent new references during the update. Or
we may be able to remove the code (perhaps, need more
investigations).
The other is rtredirect that updates a rtentry. We need
to apply our update mechanism, however it's not easy because
rtredirect is called in softint and we cannot apply our
mechanism simply. One solution is to defer rtredirect to
a workqueue but it requires some code restructuring.
- Connection state keys are not stored and loaded using the logical key
contents.
- connection finder key is stored in a map that contains the key and the
direction.
can get missing entries!). Instead, as a temporary solution, we switch
to a simple linear scan of the hash tables for the longest-prefix-match
(lpm.c lpm.h) algorithm. In fact, with few unique prefixes in the set,
on modern hardware this simple algorithm is pretty fast anyway!
In the MP-safe world, a rtentry stemming from a rtcache can be freed at any
points. So we need to protect rtentries somehow say by reference couting or
passive references. Regardless of the method, we need to call some release
function of a rtentry after using it.
The change adds a new function rtcache_unref to release a rtentry. At this
point, this function does nothing because for now we don't add a reference
to a rtentry when we get one from a rtcache. We will add something useful
in a further commit.
This change is a part of changes for MP-safe routing table. It is separated
to avoid one big change that makes difficult to debug by bisecting.
The framework provides a means to schedule if_start that will be executed
in softint later. It intends to be used to avoid calling if_start,
especially bpf_mtap, in hardware interrupt.
It adds a dedicated softint to a driver if the driver requests to use the
framework via if_deferred_start_init. The driver can schedule deferred
if_start by if_schedule_deferred_start.
Proposed and discussed on tech-kern and tech-net
(1) if set_ip_addrs and clear_ip_addrs run parallel, they can parallel call
IN_ADDRHASH_WRITER_REMOVE to the same ifa.
(2) if set_ip_addrs's workqueue is separated from clear_ip_addrs's one,
the workers can run in reverse order of enqueued.
And then, if we want to re-insert the removed pslist element, we need to
call PSLIST_ENTERY_INIT again.
advised by riastradh@n.o and reviewed by ozaki-r@n.o, thanks.
Some functions use rt_walktree to scan the routing table and delete
matched routes. However, we shouldn't use rt_walktree to delete
routes because rt_walktree is recursive to the routing table (radix
tree) and isn't friendly to MP-ification. rt_walktree allows a caller
to pass a callback function to delete an matched entry. The callback
function is called from an API of the radix tree (rn_walktree) but
also calls an API of the radix tree to delete an entry.
This change adds a new API of the radix tree, rn_search_matched,
which returns a matched entry that is selected by a callback
function passed by a caller and the caller itself deletes the
entry. By using the API, we can avoid the recursive form.
belongs.
Update the code to invoke the two routines compat_cvtcmd() and
compat_ifioctl() through indirect pointers. Initialize those
pointers in sys/net/if.c and update them in the compat module's
initialization code.
Addresses the issue pointed out in PR kern/51598
We want to ensure that a rtentry is referenced by nobody after
RTM_DELETE (except for the caller). However, rt_timer could
have a reference to the rtentry after that.
If NET_MPSAFE is enabled, don't hold KERNEL_LOCK and softnet_lock in
part of the network stack such as IP forwarding paths. The aim of the
change is to make it easy to test the network stack without the locks
and reduce our local diffs.
By default (i.e., if NET_MPSAFE isn't enabled), the locks are held
as they used to be.
Reviewed by knakahara@
If a underlying network device driver supports MSI/MSI-X, RX interrupts
can be delivered to arbitrary CPUs. This means that Layer 2 subroutines
such as ether_input (softint) and subsequent Layer 3 subroutines (softint)
which are called via traditional netisr can be dispatched on an arbitrary
CPU. Layer 2 subroutines now run without any locks (expected) and so a
Layer 2 subroutine and a Layer 3 subroutine can run in parallel.
There is a shared data between a Layer 2 routine and a Layer 3 routine,
that is ifqueue and IF_ENQUEUE (from L2) and IF_DEQUEUE (from L3) on it
are racy now.
To fix the race condition, use ifqueue#ifq_lock to protect ifqueue
instead of splnet that is meaningless now.
The same race condition exists in route_intr. Fix it as well.
Reviewed by knakahara@
has changed.
Sync address flag setup with the IPv6 counterpart.
When scrubbing the address, or setting up the address fails, restore the
old address flags as well as the old address.
rather than including in kernels with KDTRACE_HOOKS defined. Update
the dtrace_fbt module to depend on the zlib module.
Bump kernel version to avoid module mismatch.
Welcome to 7.99.38 !
required module "if_tun". This allows access to /dev/tunN to autload
the require interface module.
XXX There's might be a better place/name for net/tun.c
Before the rearrangement of ifaddr initializations (in.c,v 1.169),
when we called tun_enable via ioctl(SIOCINITIFADDR), an ifaddr
in question was inserted in the interface address list. However,
after the change the ifaddr isn't in the list at that point. So
we shouldn't rely on that we can find the ifaddr by
IFADDR_READER_FOREACH. Instead simply use the ifaddr passed by
ioctl(SIOCINITIFADDR).
Setup a command and function pointer in one case statement
instead of having a seconary case statement within a loop.
This makes the code much easier to follow, and possibly to add more compat
in the future.
Don't panic when running an old binary without compat support.
building was completed only to discover that within there lay havoc.
On the second day all just groaned and moaned, and it must be someone
else's problen.
On the third day, St. Martin stepped in and traced the culprit, which
provided inspiration, and a correction was made.
Forevermore all were agog at just how such a trivial thing could do
so much damage...
OK... to be a little less vague. The loopback interface is a truly
"special" thing, and rump knew that - and treated it very specially.
Unfortunately, when the loopback interface is changed, and rump does
not keep up, bad things happen.
This (overall) might, or might not, be the correct fix - but for now
it appears to work. If someone, sometime, finds a better way to
deal with the issues of the loopback interfaces true majesty, feel
free to revert this and do it another way.
happen automatically (via "registration" of the setup function in a
link-set), and if we're not a module, the SYSCTL_SETUP_PROTO() will
not have declared a function prototype!
This change makes struct ifaddr and its variants (in_ifaddr and in6_ifaddr)
MP-safe by using pserialize and psref. At this moment, pserialize_perform
and psref_target_destroy are disabled because (1) we don't need them
because of softnet_lock (2) they cause a deadlock because of softnet_lock.
So we'll enable them when we remove softnet_lock in the future.
netstat now uses sysctl instead of kvm(3) to get address information from
the kernel. So we can avoid the issue introduced by the reverted commit
(PR kern/51325) by updating netstat with the latest source code.
The rump code needs to call devsw_attach() in order to assign a dev_major
for bpf; it then uses this to create rumps /dev/bpf node. Unfortunately,
this leaves the devsw attached, so when the bpf module tries to initialize
itself, it gets an EEXIST error and fails.
So, once rump has figured what the dev_major should be, call devsw_detach()
to remove the devsw. Then, when the module initialization code calls
devsw_attach() it will succeed.
Timers (such as nd6_timer) typically free/destroy some data in callout
(softint). If we apply psz/psref for such data, we cannot do free/destroy
process in there because synchronization of psz/psref cannot be used in
softint. So run timer callbacks in workqueue works (normal LWP context).
Doing workqueue_enqueue a work twice (i.e., call workqueue_enqueue before
a previous task is scheduled) isn't allowed. For nd6_timer and
rt_timer_timer, this doesn't happen because callout_reset is called only
from workqueue's work. OTOH, ip{,6}flow_slowtimo's callout can be called
before its work starts and completes because the callout is periodically
called regardless of completion of the work. To avoid such a situation,
add a flag for each protocol; the flag is set true when a work is
enqueued and set false after the work finished. workqueue_enqueue is
called only if the flag is false.
Proposed on tech-net and tech-kern.
ozaki-r