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Fix a possible deadlock in TCP accepting

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Each network thread holds an array of locks, indexed by a hash
of fd. When we accept a connection we hold a lock in accepting thread.
We then generate the thread number and lock bucket for the new
connection socket - if we hit the same thread and lock bucket as
accepting socket we get a deadlock. Avoid this by checking if we're
in the same thread/lock bucket and not locking in this case.
This commit is contained in:
Witold Kręcicki
2019-05-22 12:37:03 +02:00
committed by Witold Krecicki
parent 4d498b3dac
commit 75815c1581
2 changed files with 15 additions and 2 deletions
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2
CHANGES
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@@ -1,3 +1,5 @@
5238. [bug] Fix a possible deadlock in TCP code. [GL #1046]
5237. [bug] Recurse to find the root server list with 'dig +trace'.
[GL #1028]

15
lib/isc/unix/socket.c
View File

@@ -2977,6 +2977,13 @@ internal_accept(isc__socket_t *sock) {
NEWCONNSOCK(dev)->connected = 1;
nthread = &manager->threads[NEWCONNSOCK(dev)->threadid];
/*
* We already hold a lock on one fdlock in accepting thread,
* we need to make sure that we don't double lock.
*/
bool same_bucket = (sock->threadid == NEWCONNSOCK(dev)->threadid) &&
(FDLOCK_ID(sock->fd) == lockid);
/*
* Use minimum mtu if possible.
*/
@@ -2999,13 +3006,17 @@ internal_accept(isc__socket_t *sock) {
NEWCONNSOCK(dev)->active = 1;
}
LOCK(&nthread->fdlock[lockid]);
if (!same_bucket) {
LOCK(&nthread->fdlock[lockid]);
}
nthread->fds[fd] = NEWCONNSOCK(dev);
nthread->fdstate[fd] = MANAGED;
#if defined(USE_EPOLL)
nthread->epoll_events[fd] = 0;
#endif
UNLOCK(&nthread->fdlock[lockid]);
if (!same_bucket) {
UNLOCK(&nthread->fdlock[lockid]);
}
LOCK(&manager->lock);