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

author Robert Haas <rhaas@postgresql.org>

2015年10月16日 13:42:33 +0000 (09:42 -0400)

committer Robert Haas <rhaas@postgresql.org>

2015年10月16日 13:42:33 +0000 (09:42 -0400)

Commit 2bd9e412f92bc6a68f3e8bcb18e04955cc35001d 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.

src/backend/access/transam/parallel.c patch | blob | blame | history

src/backend/libpq/pqmq.c patch | blob | blame | history

src/include/libpq/pqmq.h patch | blob | blame | history

diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c

index 29d6ed57cc251b290104c3a8faae5ab3c8302567..0b94c0f87e967b49ed1704ce9114bfd7e1c23db7 100644 (file)

--- a/src/backend/access/transam/parallel.c

+++ b/src/backend/access/transam/parallel.c

@@ -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);

diff --git a/src/backend/libpq/pqmq.c b/src/backend/libpq/pqmq.c

index 9ca6b7ce0d1b7a348f6d29a22bf83139b1e42765..0a3c2b70cbe46f68f3ad076260007a2e9db48f62 100644 (file)

--- a/src/backend/libpq/pqmq.c

+++ b/src/backend/libpq/pqmq.c

@@ -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;

diff --git a/src/include/libpq/pqmq.h b/src/include/libpq/pqmq.h

index 901756596a4717e76cb70e8d26f874e59442b50f..97f17da89db64e7cd8ce5703227852de13ee5932 100644 (file)

--- a/src/include/libpq/pqmq.h

+++ b/src/include/libpq/pqmq.h

@@ -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);

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