This commit simplifies a bit the lock management within dns_resolver_prime()
and prime_done() functions by means of turning resolver's attribute
"priming" into an atomic_bool and by creating only one dependent object on the
lock "primelock", namely the "primefetch" attribute.
By having the attribute "priming" as an atomic type, it save us from having to
use a lock just to test if priming is on or off for the given resolver context
object, within "dns_resolver_prime" function.
The "primelock" lock is still necessary, since dns_resolver_prime() function
internally calls dns_resolver_createfetch(), and whenever this function
succeeds it registers an event in the task manager which could be called by
another thread, namely the "prime_done" function, and this function is
responsible for disposing the "primefetch" attribute in the resolver object,
also for resetting "priming" attribute to false.
It is important that the invariant "priming == false AND primefetch == NULL"
remains constant, so that any thread calling "dns_resolver_prime" knows for sure
that if the "priming" attribute is false, "primefetch" attribute should also be
NULL, so a new fetch context could be created to fulfill this purpose, and
assigned to "primefetch" attribute under the lock protection.
To honor the explanation above, dns_resolver_prime is implemented as follow:
1. Atomically checks the attribute "priming" for the given resolver context.
2. If "priming" is false, assumes that "primefetch" is NULL (this is
ensured by the "prime_done" implementation), acquire "primelock"
lock and create a new fetch context, update "primefetch" pointer to
point to the newly allocated fetch context.
3. If "priming" is true, assumes that the job is already in progress,
no locks are acquired, nothing else to do.
To keep the previous invariant consistent, "prime_done" is implemented as follow:
1. Acquire "primefetch" lock.
2. Keep a reference to the current "primefetch" object;
3. Reset "primefetch" attribute to NULL.
4. Release "primefetch" lock.
5. Atomically update "priming" attribute to false.
6. Destroy the "primefetch" object by using the temporary reference.
This ensures that if "priming" is false, "primefetch" was already reset to NULL.
It doesn't make any difference in having the "priming" attribute not protected
by a lock, since the visible state of this variable would depend on the calling
order of the functions "dns_resolver_prime" and "prime_done".
As an example, suppose that instead of using an atomic for the "priming" attribute
we employed a lock to protect it.
Now suppose that "prime_done" function is called by Thread A, it is then preempted
before acquiring the lock, thus not reseting "priming" to false.
In parallel to that suppose that a Thread B is scheduled and that it calls
"dns_resolver_prime()", it then acquires the lock and check that "priming" is true,
thus it will consider that this resolver object is already priming and it won't do
any more job.
Conversely if the lock order was acquired in the other direction, Thread B would check
that "priming" is false (since prime_done acquired the lock first and set "priming" to false)
and it would initiate a priming fetch for this resolver.
An atomic variable wouldn't change this behavior, since it would behave exactly the
same, depending on the function call order, with the exception that it would avoid
having to use a lock.
There should be no side effects resulting from this change, since the previous
implementation employed use of the more general resolver's "lock" mutex, which
is used in far more contexts, but in the specifics of the "dns_resolver_prime"
and "prime_done" it was only used to protect "primefetch" and "priming" attributes,
which are not used in any of the other critical sections protected by the same lock,
thus having zero dependency on those variables.
hp implementation requires an object for each thread accessing
a hazard pointer. previous implementation had a hardcoded
HP_MAX_THREAD value of 128, which failed on machines with lots of
CPU cores (named uses 3n threads). We make isc__hp_max_threads
configurable at startup, with the value set to 4*named_g_cpus.
It's also important for this value not to be too big as we do
linear searches on a list.
The isc_refcount API that provides reference counting lost DbC checks for
overflows and underflows in the isc_refcount_{increment,decrement} functions.
The commit restores the overflow check in the isc_refcount_increment and
underflows check in the isc_refcount_decrement by checking for the previous
value to not be on the boundary.
- the socket stat counters have been moved from socket.h to stats.h.
- isc_nm_t now attaches to the same stats counter group as
isc_socketmgr_t, so that both managers can increment the same
set of statistics
- isc__nmsocket_init() now takes an interface as a paramter so that
the address family can be determined when initializing the socket.
- based on the address family and socket type, a group of statistics
counters will be associated with the socket - for example, UDP4Active
with IPv4 UDP sockets and TCP6Active with IPv6 TCP sockets. note
that no counters are currently associated with TCPDNS sockets; those
stats will be handled by the underlying TCP socket.
- the counters are not actually used by netmgr sockets yet; counter
increment and decrement calls will be added in a later commit.
After the network manager rewrite, tcp-higwater stats was only being
updated when a valid DNS query was received over tcp.
It turns out tcp-quota is updated right after a tcp connection is
accepted, before any data is read, so in the event that some client
connect but don't send a valid query, it wouldn't be taken into
account to update tcp-highwater stats, that is wrong.
This commit fix tcp-highwater to update its stats whenever a tcp connection
is established, independent of what happens after (timeout/invalid
request, etc).
The new ISC_THREAD_LOCAL macro unifies usage of platform dependent
Thread Local Storage definition thread_local vs __thread vs
__declspec(thread) to a single macro.
The commit also unifies the required level of support for TLS as for
some parts of the code it was mandatory and for some parts of the code
it wasn't.
FCTX_ATTR_SHUTTINGDOWN needs to be set and tested while holding the node
lock but the rest of the attributes don't as they are task locked. Making
fctx->attributes atomic allows both behaviours without races.
- restore support for tcp-initial-timeout, tcp-idle-timeout,
tcp-keepalive-timeout and tcp-advertised-timeout configuration
options, which were ineffective previously.
when the TCPDNS_CLIENTS_PER_CONN limit has been exceeded for a TCP
DNS connection, switch to sequential mode to ensure that memory cannot
be exhausted by too many simultaneous queries.
This allows a task to be temporary disabled so that objects won't be
processed simultaneously by libuv events and isc_task events. When a
task is paused, currently running events may complete, but no further
event will added to the run queue will be executed until the task is
unpaused.
When a task manager is created, we can now specify an `isc_nm`
object to associate with it; thereafter when the task manager is
placed into exclusive mode, the network manager will be paused.
This is a replacement for the existing isc_socket and isc_socketmgr
implementation. It uses libuv for asynchronous network communication;
"networker" objects will be distributed across worker threads reading
incoming packets and sending them for processing.
UDP listener sockets automatically create an array of "child" sockets
so each worker can listen separately.
TCP sockets are shared amongst worker threads.
A TCPDNS socket is a wrapper around a TCP socket, which handles the
the two-byte length field at the beginning of DNS messages over TCP.
(Other wrapper socket types can be implemented in the future to handle
DNS over TLS, DNS over HTTPS, etc.)
The double-locked queue implementation is still currently in use
in ns_client, but will be replaced by a fetch-and-add array queue.
This commit moves it from queue.h to list.h so that queue.h can be
used for the new data structure, and clean up dependencies between
list.h and types.h. Later, when the ISC_QUEUE is no longer is use,
it will be removed completely.
cppcheck 1.89 enabled certain value flow analysis mechanisms [1] which
trigger null pointer dereference false positives in lib/dns/rpz.c:
lib/dns/rpz.c:582:7: warning: Possible null pointer dereference: tgt_ip [nullPointer]
if (KEY_IS_IPV4(tgt_prefix, tgt_ip)) {
^
lib/dns/rpz.c:1419:44: note: Calling function 'adj_trigger_cnt', 4th argument 'NULL' value is 0
adj_trigger_cnt(rpzs, rpz_num, rpz_type, NULL, 0, true);
^
lib/dns/rpz.c:582:7: note: Null pointer dereference
if (KEY_IS_IPV4(tgt_prefix, tgt_ip)) {
^
lib/dns/rpz.c:596:7: warning: Possible null pointer dereference: tgt_ip [nullPointer]
if (KEY_IS_IPV4(tgt_prefix, tgt_ip)) {
^
lib/dns/rpz.c:1419:44: note: Calling function 'adj_trigger_cnt', 4th argument 'NULL' value is 0
adj_trigger_cnt(rpzs, rpz_num, rpz_type, NULL, 0, true);
^
lib/dns/rpz.c:596:7: note: Null pointer dereference
if (KEY_IS_IPV4(tgt_prefix, tgt_ip)) {
^
lib/dns/rpz.c:610:7: warning: Possible null pointer dereference: tgt_ip [nullPointer]
if (KEY_IS_IPV4(tgt_prefix, tgt_ip)) {
^
lib/dns/rpz.c:1419:44: note: Calling function 'adj_trigger_cnt', 4th argument 'NULL' value is 0
adj_trigger_cnt(rpzs, rpz_num, rpz_type, NULL, 0, true);
^
lib/dns/rpz.c:610:7: note: Null pointer dereference
if (KEY_IS_IPV4(tgt_prefix, tgt_ip)) {
^
It seems that cppcheck no longer treats at least some REQUIRE()
assertion failures as fatal, so add extra assertion macro definitions to
lib/isc/include/isc/util.h that are only used when the CPPCHECK
preprocessor macro is defined; these definitions make cppcheck 1.89
behave as expected.
There is an important requirement for these custom definitions to work:
cppcheck must properly treat abort() as a function which does not
return. In order for that to happen, the __GNUC__ macro must be set to
a high enough number (because system include directories are used and
system headers compile attributes away if __GNUC__ is not high enough).
__GNUC__ is thus set to the major version number of the GCC compiler
used, which is what that latter does itself during compilation.
[1] aaeec462e6
