From 79f17d45e82f3648c2459b8128ab4d516fb7640a Mon Sep 17 00:00:00 2001 From: Heikki Linnakangas Date: Wed, 8 Aug 2018 19:08:10 +0300 Subject: [PATCH] Don't run atexit callbacks in quickdie signal handlers. exit() is not async-signal safe. Even if the libc implementation is, 3rd party libraries might have installed unsafe atexit() callbacks. After receiving SIGQUIT, we really just want to exit as quickly as possible, so we don't really want to run the atexit() callbacks anyway. The original report by Jimmy Yih was a self-deadlock in startup_die(). However, this patch doesn't address that scenario; the signal handling while waiting for the startup packet is more complicated. But at least this alleviates similar problems in the SIGQUIT handlers, like that reported by Asim R P later in the same thread. Backpatch to 9.3 (all supported versions). Discussion: https://www.postgresql.org/message-id/CAOMx_OAuRUHiAuCg2YgicZLzPVv5d9_H4KrL_OFsFP%3DVPekigA%40mail.gmail.com --- src/backend/postmaster/bgworker.c | 25 ++++++++------------- src/backend/postmaster/bgwriter.c | 24 ++++++++------------ src/backend/postmaster/checkpointer.c | 24 ++++++++------------ src/backend/postmaster/startup.c | 24 ++++++++------------ src/backend/postmaster/walwriter.c | 24 ++++++++------------ src/backend/replication/walreceiver.c | 32 +++++++++++---------------- src/backend/tcop/postgres.c | 32 ++++++++++++++++----------- 7 files changed, 77 insertions(+), 108 deletions(-) diff --git a/src/backend/postmaster/bgworker.c b/src/backend/postmaster/bgworker.c index f651bb49b1..d2b695e146 100644 --- a/src/backend/postmaster/bgworker.c +++ b/src/backend/postmaster/bgworker.c @@ -644,28 +644,21 @@ SanityCheckBackgroundWorker(BackgroundWorker *worker, int elevel) static void bgworker_quickdie(SIGNAL_ARGS) { - sigaddset(&BlockSig, SIGQUIT); /* prevent nested calls */ - PG_SETMASK(&BlockSig); - - /* - * We DO NOT want to run proc_exit() callbacks -- we're here because - * shared memory may be corrupted, so we don't want to try to clean up our - * transaction. Just nail the windows shut and get out of town. Now that - * there's an atexit callback to prevent third-party code from breaking - * things by calling exit() directly, we have to reset the callbacks - * explicitly to make this work as intended. - */ - on_exit_reset(); - /* - * Note we do exit(2) not exit(0). This is to force the postmaster into a - * system reset cycle if some idiot DBA sends a manual SIGQUIT to a random + * We DO NOT want to run proc_exit() or atexit() callbacks -- we're here + * because shared memory may be corrupted, so we don't want to try to + * clean up our transaction. Just nail the windows shut and get out of + * town. The callbacks wouldn't be safe to run from a signal handler, + * anyway. + * + * Note we do _exit(2) not _exit(0). This is to force the postmaster into + * a system reset cycle if someone sends a manual SIGQUIT to a random * backend. This is necessary precisely because we don't clean up our * shared memory state. (The "dead man switch" mechanism in pmsignal.c * should ensure the postmaster sees this as a crash, too, but no harm in * being doubly sure.) */ - exit(2); + _exit(2); } /* diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c index d5ce685e54..3e6ffb05b9 100644 --- a/src/backend/postmaster/bgwriter.c +++ b/src/backend/postmaster/bgwriter.c @@ -409,27 +409,21 @@ BackgroundWriterMain(void) static void bg_quickdie(SIGNAL_ARGS) { - PG_SETMASK(&BlockSig); - /* - * We DO NOT want to run proc_exit() callbacks -- we're here because - * shared memory may be corrupted, so we don't want to try to clean up our - * transaction. Just nail the windows shut and get out of town. Now that - * there's an atexit callback to prevent third-party code from breaking - * things by calling exit() directly, we have to reset the callbacks - * explicitly to make this work as intended. - */ - on_exit_reset(); - - /* - * Note we do exit(2) not exit(0). This is to force the postmaster into a - * system reset cycle if some idiot DBA sends a manual SIGQUIT to a random + * We DO NOT want to run proc_exit() or atexit() callbacks -- we're here + * because shared memory may be corrupted, so we don't want to try to + * clean up our transaction. Just nail the windows shut and get out of + * town. The callbacks wouldn't be safe to run from a signal handler, + * anyway. + * + * Note we do _exit(2) not _exit(0). This is to force the postmaster into + * a system reset cycle if someone sends a manual SIGQUIT to a random * backend. This is necessary precisely because we don't clean up our * shared memory state. (The "dead man switch" mechanism in pmsignal.c * should ensure the postmaster sees this as a crash, too, but no harm in * being doubly sure.) */ - exit(2); + _exit(2); } /* SIGHUP: set flag to re-read config file at next convenient time */ diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c index 0950ada601..b54448017d 100644 --- a/src/backend/postmaster/checkpointer.c +++ b/src/backend/postmaster/checkpointer.c @@ -823,27 +823,21 @@ IsCheckpointOnSchedule(double progress) static void chkpt_quickdie(SIGNAL_ARGS) { - PG_SETMASK(&BlockSig); - /* - * We DO NOT want to run proc_exit() callbacks -- we're here because - * shared memory may be corrupted, so we don't want to try to clean up our - * transaction. Just nail the windows shut and get out of town. Now that - * there's an atexit callback to prevent third-party code from breaking - * things by calling exit() directly, we have to reset the callbacks - * explicitly to make this work as intended. - */ - on_exit_reset(); - - /* - * Note we do exit(2) not exit(0). This is to force the postmaster into a - * system reset cycle if some idiot DBA sends a manual SIGQUIT to a random + * We DO NOT want to run proc_exit() or atexit() callbacks -- we're here + * because shared memory may be corrupted, so we don't want to try to + * clean up our transaction. Just nail the windows shut and get out of + * town. The callbacks wouldn't be safe to run from a signal handler, + * anyway. + * + * Note we do _exit(2) not _exit(0). This is to force the postmaster into + * a system reset cycle if someone sends a manual SIGQUIT to a random * backend. This is necessary precisely because we don't clean up our * shared memory state. (The "dead man switch" mechanism in pmsignal.c * should ensure the postmaster sees this as a crash, too, but no harm in * being doubly sure.) */ - exit(2); + _exit(2); } /* SIGHUP: set flag to re-read config file at next convenient time */ diff --git a/src/backend/postmaster/startup.c b/src/backend/postmaster/startup.c index 38300527a5..2926211e35 100644 --- a/src/backend/postmaster/startup.c +++ b/src/backend/postmaster/startup.c @@ -69,27 +69,21 @@ static void StartupProcSigHupHandler(SIGNAL_ARGS); static void startupproc_quickdie(SIGNAL_ARGS) { - PG_SETMASK(&BlockSig); - - /* - * We DO NOT want to run proc_exit() callbacks -- we're here because - * shared memory may be corrupted, so we don't want to try to clean up our - * transaction. Just nail the windows shut and get out of town. Now that - * there's an atexit callback to prevent third-party code from breaking - * things by calling exit() directly, we have to reset the callbacks - * explicitly to make this work as intended. - */ - on_exit_reset(); - /* - * Note we do exit(2) not exit(0). This is to force the postmaster into a - * system reset cycle if some idiot DBA sends a manual SIGQUIT to a random + * We DO NOT want to run proc_exit() or atexit() callbacks -- we're here + * because shared memory may be corrupted, so we don't want to try to + * clean up our transaction. Just nail the windows shut and get out of + * town. The callbacks wouldn't be safe to run from a signal handler, + * anyway. + * + * Note we do _exit(2) not _exit(0). This is to force the postmaster into + * a system reset cycle if someone sends a manual SIGQUIT to a random * backend. This is necessary precisely because we don't clean up our * shared memory state. (The "dead man switch" mechanism in pmsignal.c * should ensure the postmaster sees this as a crash, too, but no harm in * being doubly sure.) */ - exit(2); + _exit(2); } diff --git a/src/backend/postmaster/walwriter.c b/src/backend/postmaster/walwriter.c index 688d5b5b80..33bbb539fe 100644 --- a/src/backend/postmaster/walwriter.c +++ b/src/backend/postmaster/walwriter.c @@ -319,27 +319,21 @@ WalWriterMain(void) static void wal_quickdie(SIGNAL_ARGS) { - PG_SETMASK(&BlockSig); - /* - * We DO NOT want to run proc_exit() callbacks -- we're here because - * shared memory may be corrupted, so we don't want to try to clean up our - * transaction. Just nail the windows shut and get out of town. Now that - * there's an atexit callback to prevent third-party code from breaking - * things by calling exit() directly, we have to reset the callbacks - * explicitly to make this work as intended. - */ - on_exit_reset(); - - /* - * Note we do exit(2) not exit(0). This is to force the postmaster into a - * system reset cycle if some idiot DBA sends a manual SIGQUIT to a random + * We DO NOT want to run proc_exit() or atexit() callbacks -- we're here + * because shared memory may be corrupted, so we don't want to try to + * clean up our transaction. Just nail the windows shut and get out of + * town. The callbacks wouldn't be safe to run from a signal handler, + * anyway. + * + * Note we do _exit(2) not _exit(0). This is to force the postmaster into + * a system reset cycle if someone sends a manual SIGQUIT to a random * backend. This is necessary precisely because we don't clean up our * shared memory state. (The "dead man switch" mechanism in pmsignal.c * should ensure the postmaster sees this as a crash, too, but no harm in * being doubly sure.) */ - exit(2); + _exit(2); } /* SIGHUP: set flag to re-read config file at next convenient time */ diff --git a/src/backend/replication/walreceiver.c b/src/backend/replication/walreceiver.c index 987bb84683..c463c119ef 100644 --- a/src/backend/replication/walreceiver.c +++ b/src/backend/replication/walreceiver.c @@ -860,27 +860,21 @@ WalRcvShutdownHandler(SIGNAL_ARGS) static void WalRcvQuickDieHandler(SIGNAL_ARGS) { - PG_SETMASK(&BlockSig); - /* - * We DO NOT want to run proc_exit() callbacks -- we're here because - * shared memory may be corrupted, so we don't want to try to clean up our - * transaction. Just nail the windows shut and get out of town. Now that - * there's an atexit callback to prevent third-party code from breaking - * things by calling exit() directly, we have to reset the callbacks - * explicitly to make this work as intended. - */ - on_exit_reset(); - - /* - * Note we do exit(2) not exit(0). This is to force the postmaster into a - * system reset cycle if some idiot DBA sends a manual SIGQUIT to a random - * backend. This is necessary precisely because we don't clean up our - * shared memory state. (The "dead man switch" mechanism in pmsignal.c - * should ensure the postmaster sees this as a crash, too, but no harm in - * being doubly sure.) + * We DO NOT want to run proc_exit() or atexit() callbacks -- we're here + * because shared memory may be corrupted, so we don't want to try to + * clean up our transaction. Just nail the windows shut and get out of + * town. The callbacks wouldn't be safe to run from a signal handler, + * anyway. + * + * Note we use _exit(2) not _exit(0). This is to force the postmaster + * into a system reset cycle if someone sends a manual SIGQUIT to a + * random backend. This is necessary precisely because we don't clean up + * our shared memory state. (The "dead man switch" mechanism in + * pmsignal.c should ensure the postmaster sees this as a crash, too, but + * no harm in being doubly sure.) */ - exit(2); + _exit(2); } /* diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c index f4133953be..07b956553a 100644 --- a/src/backend/tcop/postgres.c +++ b/src/backend/tcop/postgres.c @@ -2616,6 +2616,16 @@ quickdie(SIGNAL_ARGS) whereToSendOutput = DestNone; /* + * Notify the client before exiting, to give a clue on what happened. + * + * It's dubious to call ereport() from a signal handler. It is certainly + * not async-signal safe. But it seems better to try, than to disconnect + * abruptly and leave the client wondering what happened. It's remotely + * possible that we crash or hang while trying to send the message, but + * receiving a SIGQUIT is a sign that something has already gone badly + * wrong, so there's not much to lose. Assuming the postmaster is still + * running, it will SIGKILL us soon if we get stuck for some reason. + * * Ideally this should be ereport(FATAL), but then we'd not get control * back... */ @@ -2630,24 +2640,20 @@ quickdie(SIGNAL_ARGS) " database and repeat your command."))); /* - * We DO NOT want to run proc_exit() callbacks -- we're here because - * shared memory may be corrupted, so we don't want to try to clean up our - * transaction. Just nail the windows shut and get out of town. Now that - * there's an atexit callback to prevent third-party code from breaking - * things by calling exit() directly, we have to reset the callbacks - * explicitly to make this work as intended. - */ - on_exit_reset(); - - /* - * Note we do exit(2) not exit(0). This is to force the postmaster into a - * system reset cycle if some idiot DBA sends a manual SIGQUIT to a random + * We DO NOT want to run proc_exit() or atexit() callbacks -- we're here + * because shared memory may be corrupted, so we don't want to try to + * clean up our transaction. Just nail the windows shut and get out of + * town. The callbacks wouldn't be safe to run from a signal handler, + * anyway. + * + * Note we do _exit(2) not _exit(0). This is to force the postmaster into + * a system reset cycle if someone sends a manual SIGQUIT to a random * backend. This is necessary precisely because we don't clean up our * shared memory state. (The "dead man switch" mechanism in pmsignal.c * should ensure the postmaster sees this as a crash, too, but no harm in * being doubly sure.) */ - exit(2); + _exit(2); } /* -- 2.40.0