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Don't send protocol messages to a shm_mq that no longer exists. 

Commit 2bd9e412f9 introduced a mechanism
for relaying protocol messages from a background worker to another
backend via a shm_mq.  However, there was no provision for shutting
down the communication channel.  Therefore, a protocol message sent
late in the shutdown sequence, such as a DEBUG message resulting from
cranking up log_min_messages, could crash the server.  To fix, install
an on_dsm_detach callback that disables sending messages to the shm_mq
when the associated DSM is detached.
This commit is contained in:
Robert Haas 2015-10-16 09:42:33 -04:00
parent 3587cbc34f
commit 2ad5c27bb5
3 changed files with 28 additions and 4 deletions
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2
src/backend/access/transam/parallel.c
View File

@ -867,7 +867,7 @@ ParallelWorkerMain(Datum main_arg)
ParallelWorkerNumber * PARALLEL_ERROR_QUEUE_SIZE);
shm_mq_set_sender(mq, MyProc);
mqh = shm_mq_attach(mq, seg, NULL);
pq_redirect_to_shm_mq(mq, mqh);
pq_redirect_to_shm_mq(seg, mqh);
pq_set_parallel_master(fps->parallel_master_pid,
fps->parallel_master_backend_id);

28
src/backend/libpq/pqmq.c
View File

@ -26,6 +26,7 @@ static bool pq_mq_busy = false;
static pid_t pq_mq_parallel_master_pid = 0;
static pid_t pq_mq_parallel_master_backend_id = InvalidBackendId;
static void pq_cleanup_redirect_to_shm_mq(dsm_segment *seg, Datum arg);
static void mq_comm_reset(void);
static int mq_flush(void);
static int mq_flush_if_writable(void);
@ -51,13 +52,26 @@ static PQcommMethods PqCommMqMethods = {
* message queue.
*/
void
pq_redirect_to_shm_mq(shm_mq *mq, shm_mq_handle *mqh)
pq_redirect_to_shm_mq(dsm_segment *seg, shm_mq_handle *mqh)
{
PqCommMethods = &PqCommMqMethods;
pq_mq = mq;
pq_mq = shm_mq_get_queue(mqh);
pq_mq_handle = mqh;
whereToSendOutput = DestRemote;
FrontendProtocol = PG_PROTOCOL_LATEST;
on_dsm_detach(seg, pq_cleanup_redirect_to_shm_mq, (Datum) 0);
}
/*
* When the DSM that contains our shm_mq goes away, we need to stop sending
* messages to it.
*/
static void
pq_cleanup_redirect_to_shm_mq(dsm_segment *seg, Datum arg)
{
pq_mq = NULL;
pq_mq_handle = NULL;
whereToSendOutput = DestNone;
}
/*
@ -123,9 +137,19 @@ mq_putmessage(char msgtype, const char *s, size_t len)
if (pq_mq != NULL)
shm_mq_detach(pq_mq);
pq_mq = NULL;
pq_mq_handle = NULL;
return EOF;
}
/*
* If the message queue is already gone, just ignore the message. This
* doesn't necessarily indicate a problem; for example, DEBUG messages
* can be generated late in the shutdown sequence, after all DSMs have
* already been detached.
*/
if (pq_mq == NULL)
return 0;
pq_mq_busy = true;
iov[0].data = &msgtype;

2
src/include/libpq/pqmq.h
View File

@ -16,7 +16,7 @@
#include "lib/stringinfo.h"
#include "storage/shm_mq.h"
extern void pq_redirect_to_shm_mq(shm_mq *, shm_mq_handle *);
extern void pq_redirect_to_shm_mq(dsm_segment *seg, shm_mq_handle *mqh);
extern void pq_set_parallel_master(pid_t pid, BackendId backend_id);
extern void pq_parse_errornotice(StringInfo str, ErrorData *edata);