From 4f3027b35d5f25da37836b68d81fbcfb077e41d5 Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Sat, 14 May 2022 10:15:30 +1200 Subject: [PATCH v2] Don't trust signalfd() on illumos. Allow the choice between signalfd vs self-pipe to be controlled independently of the choice between epoll() and poll(). Make the default choice the same as before (signalfd + epoll() for Linux systems, self-pipe + poll() for other Unixes that don't have kqueue), except on illumos where it's self-pipe + epoll(). We don't have a very good understanding of why, yet, but its signalfd doesn't seem to behave the same as Linux in some edge case that leads to lost wakeups. This way, illumos users get a working default that doesn't give up the benefits of epoll() over poll(). Back-patch to 14, where use of signalfd() appeared. Discussion: https://postgr.es/m/MEYP282MB1669C8D88F0997354C2313C1B6CA9%40MEYP282MB1669.AUSP282.PROD.OUTLOOK.COM --- src/backend/storage/ipc/latch.c | 58 +++++++++++++++++++++++---------- 1 file changed, 40 insertions(+), 18 deletions(-) diff --git a/src/backend/storage/ipc/latch.c b/src/backend/storage/ipc/latch.c index 78c6a89271..c99dbb9f46 100644 --- a/src/backend/storage/ipc/latch.c +++ b/src/backend/storage/ipc/latch.c @@ -72,7 +72,7 @@ #if defined(WAIT_USE_EPOLL) || defined(WAIT_USE_POLL) || \ defined(WAIT_USE_KQUEUE) || defined(WAIT_USE_WIN32) /* don't overwrite manual choice */ -#elif defined(HAVE_SYS_EPOLL_H) && defined(HAVE_SYS_SIGNALFD_H) +#elif defined(HAVE_SYS_EPOLL_H) #define WAIT_USE_EPOLL #elif defined(HAVE_KQUEUE) #define WAIT_USE_KQUEUE @@ -84,6 +84,22 @@ #error "no wait set implementation available" #endif +/* + * By default, we use a self-pipe with poll() and a signalfd with epoll(), if + * available. We avoid signalfd on illumos because it doesn't seem to work + * reliably. For testing the choice can also be manually specified. + */ +#if defined(WAIT_USE_POLL) || defined(WAIT_USE_EPOLL) +#if defined(WAIT_USE_SELF_PIPE) || defined(WAIT_USE_SIGNALFD) +/* don't overwrite manual choice */ +#elif defined(WAIT_USE_EPOLL) && defined(HAVE_SYS_SIGNALFD_H) && \ + !defined(__sun__) +#define WAIT_USE_SIGNALFD +#else +#define WAIT_USE_SELF_PIPE +#endif +#endif + /* typedef in latch.h */ struct WaitEventSet { @@ -146,12 +162,12 @@ static WaitEventSet *LatchWaitSet; static volatile sig_atomic_t waiting = false; #endif -#ifdef WAIT_USE_EPOLL +#ifdef WAIT_USE_SIGNALFD /* On Linux, we'll receive SIGURG via a signalfd file descriptor. */ static int signal_fd = -1; #endif -#if defined(WAIT_USE_POLL) +#ifdef WAIT_USE_SELF_PIPE /* Read and write ends of the self-pipe */ static int selfpipe_readfd = -1; static int selfpipe_writefd = -1; @@ -164,7 +180,7 @@ static void latch_sigurg_handler(SIGNAL_ARGS); static void sendSelfPipeByte(void); #endif -#if defined(WAIT_USE_POLL) || defined(WAIT_USE_EPOLL) +#if defined(WAIT_USE_SELF_PIPE) || defined(WAIT_USE_SIGNALFD) static void drain(void); #endif @@ -190,7 +206,7 @@ static inline int WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout, void InitializeLatchSupport(void) { -#if defined(WAIT_USE_POLL) +#if defined(WAIT_USE_SELF_PIPE) int pipefd[2]; if (IsUnderPostmaster) @@ -264,7 +280,7 @@ InitializeLatchSupport(void) pqsignal(SIGURG, latch_sigurg_handler); #endif -#ifdef WAIT_USE_EPOLL +#ifdef WAIT_USE_SIGNALFD sigset_t signalfd_mask; /* Block SIGURG, because we'll receive it through a signalfd. */ @@ -316,7 +332,7 @@ ShutdownLatchSupport(void) LatchWaitSet = NULL; } -#if defined(WAIT_USE_POLL) +#if defined(WAIT_USE_SELF_PIPE) close(selfpipe_readfd); close(selfpipe_writefd); selfpipe_readfd = -1; @@ -324,7 +340,7 @@ ShutdownLatchSupport(void) selfpipe_owner_pid = InvalidPid; #endif -#if defined(WAIT_USE_EPOLL) +#if defined(WAIT_USE_SIGNALFD) close(signal_fd); signal_fd = -1; #endif @@ -341,9 +357,12 @@ InitLatch(Latch *latch) latch->owner_pid = MyProcPid; latch->is_shared = false; -#if defined(WAIT_USE_POLL) +#if defined(WAIT_USE_SELF_PIPE) /* Assert InitializeLatchSupport has been called in this process */ Assert(selfpipe_readfd >= 0 && selfpipe_owner_pid == MyProcPid); +#elif defined(WAIT_USE_SIGNALFD) + /* Assert InitializeLatchSupport has been called in this process */ + Assert(signal_fd >= 0); #elif defined(WAIT_USE_WIN32) latch->event = CreateEvent(NULL, TRUE, FALSE, NULL); if (latch->event == NULL) @@ -405,9 +424,12 @@ OwnLatch(Latch *latch) /* Sanity checks */ Assert(latch->is_shared); -#if defined(WAIT_USE_POLL) +#if defined(WAIT_USE_SELF_PIPE) /* Assert InitializeLatchSupport has been called in this process */ Assert(selfpipe_readfd >= 0 && selfpipe_owner_pid == MyProcPid); +#elif defined(WAIT_USE_SIGNALFD) + /* Assert InitializeLatchSupport has been called in this process */ + Assert(signal_fd >= 0); #endif if (latch->owner_pid != 0) @@ -617,7 +639,7 @@ SetLatch(Latch *latch) return; else if (owner_pid == MyProcPid) { -#if defined(WAIT_USE_POLL) +#if defined(WAIT_USE_SELF_PIPE) if (waiting) sendSelfPipeByte(); #else @@ -904,9 +926,9 @@ AddWaitEventToSet(WaitEventSet *set, uint32 events, pgsocket fd, Latch *latch, { set->latch = latch; set->latch_pos = event->pos; -#if defined(WAIT_USE_POLL) +#if defined(WAIT_USE_SELF_PIPE) event->fd = selfpipe_readfd; -#elif defined(WAIT_USE_EPOLL) +#elif defined(WAIT_USE_SIGNALFD) event->fd = signal_fd; #else event->fd = PGINVALID_SOCKET; @@ -2083,7 +2105,7 @@ GetNumRegisteredWaitEvents(WaitEventSet *set) return set->nevents; } -#if defined(WAIT_USE_POLL) +#if defined(WAIT_USE_SELF_PIPE) /* * SetLatch uses SIGURG to wake up the process waiting on the latch. @@ -2134,7 +2156,7 @@ retry: #endif -#if defined(WAIT_USE_POLL) || defined(WAIT_USE_EPOLL) +#if defined(WAIT_USE_SELF_PIPE) || defined(WAIT_USE_SIGNALFD) /* * Read all available data from self-pipe or signalfd. @@ -2150,7 +2172,7 @@ drain(void) int rc; int fd; -#ifdef WAIT_USE_POLL +#ifdef WAIT_USE_SELF_PIPE fd = selfpipe_readfd; #else fd = signal_fd; @@ -2168,7 +2190,7 @@ drain(void) else { waiting = false; -#ifdef WAIT_USE_POLL +#ifdef WAIT_USE_SELF_PIPE elog(ERROR, "read() on self-pipe failed: %m"); #else elog(ERROR, "read() on signalfd failed: %m"); @@ -2178,7 +2200,7 @@ drain(void) else if (rc == 0) { waiting = false; -#ifdef WAIT_USE_POLL +#ifdef WAIT_USE_SELF_PIPE elog(ERROR, "unexpected EOF on self-pipe"); #else elog(ERROR, "unexpected EOF on signalfd"); -- 2.30.2