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BUG/MINOR: quic: fix race on quic_conns list during affinity rebind 

Each quic_conn are attached in a global thread-local quic_conns list
used for "show quic" command. During thread rebinding, a connection is
detached from its local list instance and moved to its new thread list.
However this operation is not thread-safe and may cause a race
condition.

To fix this, only remove the connection from its list inside
qc_set_tid_affinity(). The connection is inserted only after in
qc_finalize_affinity_rebind() on the new thread instance thus prevented
a race condition. One impact of this is that a connection will be
invisible during rebinding for "show quic".

A connection must not transition to closing state in between this two
steps or else cleanup via quic_handle_stopping() may not miss it. To
ensure this, this patch relies on the previous commit :
  commit d6646dddcc
  MINOR: quic: finalize affinity change as soon as possible

This should be backported up to 2.7.
This commit is contained in:
Amaury Denoyelle 2023-04-26 16:12:12 +02:00
parent d6646dddcc
commit 7b516d3732
1 changed files with 13 additions and 5 deletions
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18
src/quic_conn.c
View File

@ -8524,12 +8524,10 @@ int qc_set_tid_affinity(struct quic_conn *qc, uint new_tid, struct listener *new
fd_migrate_on(qc->fd, new_tid);
}
/* Remove conn from per-thread list instance. */
/* Remove conn from per-thread list instance. It will be hidden from
* "show quic" until rebinding is completed.
*/
qc_detach_th_ctx_list(qc, 0);
/* Connection must not be closing or else it must be inserted in quic_conns_clo list instance instead. */
BUG_ON(qc->flags & (QUIC_FL_CONN_CLOSING|QUIC_FL_CONN_DRAINING));
LIST_APPEND(&ha_thread_ctx[new_tid].quic_conns, &qc->el_th_ctx);
qc->qc_epoch = HA_ATOMIC_LOAD(&qc_epoch);
node = eb64_first(&qc->cids);
BUG_ON(!node || eb64_next(node)); /* One and only one CID must be present before affinity rebind. */
@ -8569,6 +8567,16 @@ void qc_finalize_affinity_rebind(struct quic_conn *qc)
BUG_ON(!(qc->flags & QUIC_FL_CONN_AFFINITY_CHANGED));
qc->flags &= ~QUIC_FL_CONN_AFFINITY_CHANGED;
/* A connection must not pass to closing state until affinity rebind
* is completed. Else quic_handle_stopping() may miss it during process
* stopping cleanup.
*/
BUG_ON(qc->flags & (QUIC_FL_CONN_CLOSING|QUIC_FL_CONN_DRAINING));
/* Reinsert connection in ha_thread_ctx global list. */
LIST_APPEND(&th_ctx->quic_conns, &qc->el_th_ctx);
qc->qc_epoch = HA_ATOMIC_LOAD(&qc_epoch);
/* Reactivate FD polling if connection socket is active. */
qc_want_recv(qc);