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Commit2ad5c27

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Don't send protocol messages to a shm_mq that no longer exists.
Commit2bd9e41 introduced a mechanismfor relaying protocol messages from a background worker to anotherbackend via a shm_mq. However, there was no provision for shuttingdown the communication channel. Therefore, a protocol message sentlate in the shutdown sequence, such as a DEBUG message resulting fromcranking up log_min_messages, could crash the server. To fix, installan on_dsm_detach callback that disables sending messages to the shm_mqwhen the associated DSM is detached.
1 parent3587cbc commit2ad5c27

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3 files changed

+28
-4
lines changed

3 files changed

+28
-4
lines changed

‎src/backend/access/transam/parallel.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -867,7 +867,7 @@ ParallelWorkerMain(Datum main_arg)
867867
ParallelWorkerNumber*PARALLEL_ERROR_QUEUE_SIZE);
868868
shm_mq_set_sender(mq,MyProc);
869869
mqh=shm_mq_attach(mq,seg,NULL);
870-
pq_redirect_to_shm_mq(mq,mqh);
870+
pq_redirect_to_shm_mq(seg,mqh);
871871
pq_set_parallel_master(fps->parallel_master_pid,
872872
fps->parallel_master_backend_id);
873873

‎src/backend/libpq/pqmq.c

Lines changed: 26 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -26,6 +26,7 @@ static bool pq_mq_busy = false;
2626
staticpid_tpq_mq_parallel_master_pid=0;
2727
staticpid_tpq_mq_parallel_master_backend_id=InvalidBackendId;
2828

29+
staticvoidpq_cleanup_redirect_to_shm_mq(dsm_segment*seg,Datumarg);
2930
staticvoidmq_comm_reset(void);
3031
staticintmq_flush(void);
3132
staticintmq_flush_if_writable(void);
@@ -51,13 +52,26 @@ static PQcommMethods PqCommMqMethods = {
5152
* message queue.
5253
*/
5354
void
54-
pq_redirect_to_shm_mq(shm_mq*mq,shm_mq_handle*mqh)
55+
pq_redirect_to_shm_mq(dsm_segment*seg,shm_mq_handle*mqh)
5556
{
5657
PqCommMethods=&PqCommMqMethods;
57-
pq_mq=mq;
58+
pq_mq=shm_mq_get_queue(mqh);
5859
pq_mq_handle=mqh;
5960
whereToSendOutput=DestRemote;
6061
FrontendProtocol=PG_PROTOCOL_LATEST;
62+
on_dsm_detach(seg,pq_cleanup_redirect_to_shm_mq, (Datum)0);
63+
}
64+
65+
/*
66+
* When the DSM that contains our shm_mq goes away, we need to stop sending
67+
* messages to it.
68+
*/
69+
staticvoid
70+
pq_cleanup_redirect_to_shm_mq(dsm_segment*seg,Datumarg)
71+
{
72+
pq_mq=NULL;
73+
pq_mq_handle=NULL;
74+
whereToSendOutput=DestNone;
6175
}
6276

6377
/*
@@ -123,9 +137,19 @@ mq_putmessage(char msgtype, const char *s, size_t len)
123137
if (pq_mq!=NULL)
124138
shm_mq_detach(pq_mq);
125139
pq_mq=NULL;
140+
pq_mq_handle=NULL;
126141
returnEOF;
127142
}
128143

144+
/*
145+
* If the message queue is already gone, just ignore the message. This
146+
* doesn't necessarily indicate a problem; for example, DEBUG messages
147+
* can be generated late in the shutdown sequence, after all DSMs have
148+
* already been detached.
149+
*/
150+
if (pq_mq==NULL)
151+
return0;
152+
129153
pq_mq_busy= true;
130154

131155
iov[0].data=&msgtype;

‎src/include/libpq/pqmq.h

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -16,7 +16,7 @@
1616
#include"lib/stringinfo.h"
1717
#include"storage/shm_mq.h"
1818

19-
externvoidpq_redirect_to_shm_mq(shm_mq*,shm_mq_handle*);
19+
externvoidpq_redirect_to_shm_mq(dsm_segment*seg,shm_mq_handle*mqh);
2020
externvoidpq_set_parallel_master(pid_tpid,BackendIdbackend_id);
2121

2222
externvoidpq_parse_errornotice(StringInfostr,ErrorData*edata);

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