tree 537a7cb02ab0f7615489313351a336cd26fb0fa2
parent 1304d19dee7cf9f703a24be9e5c00b862a62a10a
author Amaury Denoyelle <adenoyelle@haproxy.com> 1680709925 +0200
committer Amaury Denoyelle <adenoyelle@haproxy.com> 1681830514 +0200

MEDIUM: quic: implement thread affinity rebinding

Implement a new function qc_set_tid_affinity(). This function is
responsible to rebind a quic_conn instance to a new thread.

This operation consists mostly of releasing existing tasks and tasklet
and allocating new instances on the new thread. If the quic_conn uses
its owned socket, it is also migrated to the new thread. The migration
is finally completed with updated the CID TID to the new thread. After
this step, the connection is thus accessible to the new thread and
cannot be access anymore on the old one without risking race condition.

To ensure rebinding is either done completely or not at all, tasks and
tasklet are pre-allocated before all operations. If this fails, an error
is returned and rebiding is not done.

To destroy the older tasklet, its context is set to NULL before wake up.
In I/O callbacks, a new function qc_process() is used to check context
and free the tasklet if NULL.

The thread rebinding can cause a race condition if the older thread
quic_dghdlrs::dgrams list contains datagram for the connection after
rebinding is done. To prevent this, quic_rx_pkt_retrieve_conn() always
check if the packet CID is still associated to the current thread or
not. In the latter case, no connection is returned and the new thread is
returned to allow to redispatch the datagram to the new thread in a
thread-safe way.

This should be backported up to 2.7 after a period of observation.