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MXS-1805 Force all maxadmin connections to main thread

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If maxadmin connections are handled by different workers, then
there may be a deadlock if some maxadmin command requires
communication with all workers.

Namely, in that case a message will be sent to all other workers
but the current one, but that message will not be handled if that
other worker at that point sits in the debugcmd_lock spinlock
in debugcmd.c:execute_cmd().

We can prevent that deadlock from happening simply by ensuring
that all maxadmin connections are handled by one thread.
This commit is contained in:
Johan Wikman 2018-04-16 13:25:33 +03:00
parent 3d8d2beaaa
commit 7e29725050
1 changed files with 12 additions and 0 deletions
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12
server/core/dcb.cc
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@ -3419,6 +3419,18 @@ int poll_add_dcb(DCB *dcb)
new_state = DCB_STATE_LISTENING;
worker_id = MXS_WORKER_ALL;
}
else if (dcb->dcb_role == DCB_ROLE_CLIENT_HANDLER &&
(strcasecmp(dcb->service->routerModule, "cli") == 0))
{
// If the DCB refers to an accepted maxadmin socket, we force it
// to the main thread. That's done in order to prevent a deadlock
// that may happen if there are multiple concurrent maxadmin calls,
// handled by different worker threads.
// See: https://jira.mariadb.org/browse/MXS-1805
new_state = DCB_STATE_POLLING;
dcb->poll.thread.id = 0;
worker_id = dcb->poll.thread.id;
}
else
{
ss_dassert(dcb->dcb_role == DCB_ROLE_CLIENT_HANDLER ||