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Block interrupts during HandleParallelMessages(). 

As noted by Alvaro, there are CHECK_FOR_INTERRUPTS() calls in the shm_mq.c
functions called by HandleParallelMessages().  I believe they're all
unreachable since we always pass nowait = true, but it doesn't seem like
a great idea to assume that no such call will ever be reachable from
HandleParallelMessages().  If that did happen, there would be a risk of a
recursive call to HandleParallelMessages(), which it does not appear to be
designed for --- for example, there's nothing that would prevent
out-of-order processing of received messages.  And certainly such cases
cannot easily be tested.  So let's prevent it by holding off interrupts for
the duration of the function.  Back-patch to 9.5 which contains identical
code.

Discussion: <14869.1470083848@sss.pgh.pa.us>
This commit is contained in:
Tom Lane 2016-08-02 16:39:16 -04:00
parent c4d3a039f0
commit b6a97b91ff
1 changed files with 16 additions and 5 deletions
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21
src/backend/access/transam/parallel.c
View File

@ -704,14 +704,21 @@ HandleParallelMessages(void)
{
dlist_iter iter;
/*
* This is invoked from ProcessInterrupts(), and since some of the
* functions it calls contain CHECK_FOR_INTERRUPTS(), there is a potential
* for recursive calls if more signals are received while this runs. It's
* unclear that recursive entry would be safe, and it doesn't seem useful
* even if it is safe, so let's block interrupts until done.
*/
HOLD_INTERRUPTS();
ParallelMessagePending = false;
dlist_foreach(iter, &pcxt_list)
{
ParallelContext *pcxt;
int i;
Size nbytes;
void *data;
pcxt = dlist_container(ParallelContext, node, iter.cur);
if (pcxt->worker == NULL)
@ -721,13 +728,15 @@ HandleParallelMessages(void)
{
/*
* Read as many messages as we can from each worker, but stop when
* either (1) the error queue goes away, which can happen if we
* receive a Terminate message from the worker; or (2) no more
* messages can be read from the worker without blocking.
* either (1) the worker's error queue goes away, which can happen
* if we receive a Terminate message from the worker; or (2) no
* more messages can be read from the worker without blocking.
*/
while (pcxt->worker[i].error_mqh != NULL)
{
shm_mq_result res;
Size nbytes;
void *data;
res = shm_mq_receive(pcxt->worker[i].error_mqh, &nbytes,
&data, true);
@ -749,6 +758,8 @@ HandleParallelMessages(void)
}
}
}
RESUME_INTERRUPTS();
}
/*