On 9/14/2016 7:14 AM, Fraser Tweedale wrote:
Hi team,
The attached patch fixes (yet another) race condition in
LDAPProfileSubsystem.
https://fedorahosted.org/pki/ticket/2453
Additional context: https://fedorahosted.org/freeipa/ticket/6274
Thanks,
Fraser
The patch looks fine, but probably it can be simplified like this:
class LDAPProfileSubsystem {
void init() {
// load initial profiles
repository = new LDAPProfileRepository();
repository.load();
// monitor profile changes in the background
monitor = new Thread(repository);
monitor.start();
}
IProfile getProfile(id) {
return repository.getProfile(id);
}
}
class LDAPProfileRepository {
LinkedHashMap profiles = ...
void synchronized load() {
// create persistent search
conn = dbFactory.getConn();
results = conn.search(...);
// get number of profiles
entry = results.next();
numProfiles = entry.getAttribute("numSubordinates");
for (i=0; i<numProfiles; i++) {
// read profile
entry = results.next();
readProfile(entry);
}
}
void synchronized readProfile() {
...
}
IProfile synchronized getProfile(id) {
return profiles.get(id);
}
void run() {
while (true) {
try {
// process profile changes
while (results.hasMoreElements()) {
entry = results.next();
...
}
} catch (...) {
// reconnect
load();
}
}
}
}
So the load() will block during initialization and will also block
readers during reload after reconnect. We probably can replace
"synchronized" with ReadWriteLock to allow concurrent readers.
Feel free to push the patch as is (assuming it's well tested). We can
make further improvements later on.
One thing though, I highly suggest that we fix this issue on both Fedora
and RHEL/CentOS platforms. The patch is non-trivial, so the behavior
could be different if not applied consistently. Since PKI is developed
mainly on Fedora but used on different platforms, it would be much
easier to troubleshoot issues by keeping the behavior consistent across
platforms, especially on anything related to concurrency.
We don't need to create new builds for all platforms at the same time,
but we should at least push this patch to all 10.3 branches so it can be
picked up in the next 10.3 build of the corresponding platform.
--
Endi S. Dewata
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