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MXS-2259: Fix double addition of DCBs to worker list

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When poll_add_dcb was called for a DCB that once was polling system but
was subsequently removed, the DCB would appear twice in the worker's list
of DCBs. This caused a hang when the DCB was the last one in the worker's
list and dcb_foreach_local would be called.

To prevent the aforementioned problem, the DCBs are now added and removed
directly to and from the workers instead of indirectly via poll_add_dcb
and poll_remove_dcb.
This commit is contained in:
Markus Mäkelä 2019-01-14 21:43:09 +02:00
parent 57fe5ff56a
commit db98ecbaa1
No known key found for this signature in database
GPG Key ID: 72D48FCE664F7B19
1 changed files with 36 additions and 11 deletions
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47
server/core/dcb.cc
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@ -65,6 +65,12 @@ using maxbase::Worker;
#define DCB_EH_NOTICE(s, p)
#endif
#ifdef EPOLLRDHUP
constexpr uint32_t poll_events = EPOLLIN | EPOLLOUT | EPOLLRDHUP | EPOLLHUP | EPOLLET;
#else
constexpr uint32_t poll_events = EPOLLIN | EPOLLOUT | EPOLLHUP | EPOLLET;
#endif
namespace
{
@ -2826,6 +2832,7 @@ static void dcb_add_to_list(DCB* dcb)
}
else
{
mxb_assert(this_unit.all_dcbs[id]->thread.tail->thread.next != dcb);
this_unit.all_dcbs[id]->thread.tail->thread.next = dcb;
this_unit.all_dcbs[id]->thread.tail = dcb;
}
@ -2989,6 +2996,8 @@ void dcb_foreach_local(bool (* func)(DCB* dcb, void* data), void* data)
for (DCB* dcb = this_unit.all_dcbs[thread_id]; dcb; dcb = dcb->thread.next)
{
mxb_assert(dcb->thread.next != dcb);
if (!func(dcb, data))
{
break;
@ -3568,13 +3577,7 @@ int poll_add_dcb(DCB* dcb)
{
dcb_sanity_check(dcb);
uint32_t events = 0;
#ifdef EPOLLRDHUP
events = EPOLLIN | EPOLLOUT | EPOLLRDHUP | EPOLLHUP | EPOLLET;
#else
events = EPOLLIN | EPOLLOUT | EPOLLHUP | EPOLLET;
#endif
uint32_t events = poll_events;
/** Choose new state and worker thread ID according to the role of DCB. */
dcb_state_t new_state;
@ -3726,13 +3729,23 @@ DCB* dcb_get_current()
static int upstream_throttle_callback(DCB* dcb, DCB_REASON reason, void* userdata)
{
DCB* client_dcb = dcb->session->client_dcb;
mxb::Worker* worker = static_cast<mxb::Worker*>(client_dcb->poll.owner);
// The fd is removed manually here due to the fact that poll_add_dcb causes the DCB to be added to the
// worker's list of DCBs but poll_remove_dcb doesn't remove it from it. This is due to the fact that the
// DCBs are only removed from the list when they are closed.
if (reason == DCB_REASON_HIGH_WATER)
{
poll_remove_dcb(client_dcb);
MXS_INFO("High water mark hit for '%s'@'%s', not reading data until low water mark is hit",
client_dcb->user, client_dcb->remote);
worker->remove_fd(client_dcb->fd);
client_dcb->state = DCB_STATE_NOPOLLING;
}
else if (reason == DCB_REASON_LOW_WATER)
{
poll_add_dcb(client_dcb);
MXS_INFO("Low water mark hit for '%s'@'%s', accepting new data", client_dcb->user, client_dcb->remote);
worker->add_fd(client_dcb->fd, poll_events, (MXB_POLL_DATA*)client_dcb);
client_dcb->state = DCB_STATE_POLLING;
}
return 0;
@ -3744,7 +3757,13 @@ bool backend_dcb_remove_func(DCB* dcb, void* data)
if (dcb->session == session && dcb->dcb_role == DCB_ROLE_BACKEND_HANDLER)
{
poll_remove_dcb(dcb);
DCB* client_dcb = dcb->session->client_dcb;
MXS_INFO("High water mark hit for connection to '%s' from %s'@'%s', not reading data until low water "
"mark is hit", dcb->server->name, client_dcb->user, client_dcb->remote);
mxb::Worker* worker = static_cast<mxb::Worker*>(dcb->poll.owner);
worker->remove_fd(dcb->fd);
dcb->state = DCB_STATE_NOPOLLING;
}
return true;
@ -3756,7 +3775,13 @@ bool backend_dcb_add_func(DCB* dcb, void* data)
if (dcb->session == session && dcb->dcb_role == DCB_ROLE_BACKEND_HANDLER)
{
poll_add_dcb(dcb);
DCB* client_dcb = dcb->session->client_dcb;
MXS_INFO("Low water mark hit for connection to '%s' from '%s'@'%s', accepting new data",
dcb->server->name, client_dcb->user, client_dcb->remote);
mxb::Worker* worker = static_cast<mxb::Worker*>(dcb->poll.owner);
worker->add_fd(dcb->fd, poll_events, (MXB_POLL_DATA*)dcb);
dcb->state = DCB_STATE_POLLING;
}
return true;