From 197e4af9d5da180190a0f2be851b095dba57d9cd Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Fri, 19 Oct 2018 13:59:14 +1300 Subject: [PATCH] Refactor pid, random seed and start time initialization. Background workers, including parallel workers, were generating the same sequence of numbers in random(). This showed up as DSM handle collisions when Parallel Hash created multiple segments, but any code that calls random() in background workers could be affected if it cares about different backends generating different numbers. Repair by making sure that all new processes initialize the seed at the same time as they set MyProcPid and MyStartTime in a new function InitProcessGlobals(), called by the postmaster, its children and also standalone processes. Also add a new high resolution MyStartTimestamp as a potentially useful by-product, and remove SessionStartTime from struct Port as it is now redundant. No back-patch for now, as the known consequences so far are just a bunch of harmless shm_open(O_EXCL) collisions. Author: Thomas Munro Reviewed-by: Tom Lane Discussion: https://postgr.es/m/CAEepm%3D2eJj_6%3DB%2B2tEpGu2nf1BjthCf9nXXUouYvJJ4C5WSwhg%40mail.gmail.com --- src/backend/postmaster/pgstat.c | 10 +---- src/backend/postmaster/postmaster.c | 60 ++++++++++++++--------------- src/backend/tcop/postgres.c | 2 +- src/backend/utils/init/globals.c | 1 + src/backend/utils/init/miscinit.c | 16 +------- src/include/libpq/libpq-be.h | 7 ---- src/include/miscadmin.h | 2 + src/include/postmaster/postmaster.h | 1 + 8 files changed, 37 insertions(+), 62 deletions(-) diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c index 8a5b2b3b42..8de603d193 100644 --- a/src/backend/postmaster/pgstat.c +++ b/src/backend/postmaster/pgstat.c @@ -2784,21 +2784,13 @@ pgstat_initialize(void) void pgstat_bestart(void) { - TimestampTz proc_start_timestamp; SockAddr clientaddr; volatile PgBackendStatus *beentry; /* * To minimize the time spent modifying the PgBackendStatus entry, fetch * all the needed data first. - * - * If we have a MyProcPort, use its session start time (for consistency, - * and to save a kernel call). */ - if (MyProcPort) - proc_start_timestamp = MyProcPort->SessionStartTime; - else - proc_start_timestamp = GetCurrentTimestamp(); /* * We may not have a MyProcPort (eg, if this is the autovacuum process). @@ -2883,7 +2875,7 @@ pgstat_bestart(void) } while ((beentry->st_changecount & 1) == 0); beentry->st_procpid = MyProcPid; - beentry->st_proc_start_timestamp = proc_start_timestamp; + beentry->st_proc_start_timestamp = MyStartTimestamp; beentry->st_activity_start_timestamp = 0; beentry->st_state_start_timestamp = 0; beentry->st_xact_start_timestamp = 0; diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c index 41de140ae0..688f462e7d 100644 --- a/src/backend/postmaster/postmaster.c +++ b/src/backend/postmaster/postmaster.c @@ -129,6 +129,7 @@ #include "utils/pidfile.h" #include "utils/ps_status.h" #include "utils/timeout.h" +#include "utils/timestamp.h" #include "utils/varlena.h" #ifdef EXEC_BACKEND @@ -581,9 +582,9 @@ PostmasterMain(int argc, char *argv[]) int i; char *output_config_variable = NULL; - MyProcPid = PostmasterPid = getpid(); + InitProcessGlobals(); - MyStartTime = time(NULL); + PostmasterPid = MyProcPid; IsPostmasterEnvironment = true; @@ -597,16 +598,6 @@ PostmasterMain(int argc, char *argv[]) */ umask(PG_MODE_MASK_OWNER); - /* - * Initialize random(3) so we don't get the same values in every run. - * - * Note: the seed is pretty predictable from externally-visible facts such - * as postmaster start time, so avoid using random() for security-critical - * random values during postmaster startup. At the time of first - * connection, PostmasterRandom will select a hopefully-more-random seed. - */ - srandom((unsigned int) (MyProcPid ^ MyStartTime)); - /* * By default, palloc() requests in the postmaster will be allocated in * the PostmasterContext, which is space that can be recycled by backends. @@ -2513,6 +2504,32 @@ ClosePostmasterPorts(bool am_syslogger) } +/* + * InitProcessGlobals -- set MyProcPid, MyStartTime[stamp], random seeds + * + * Called early in every backend. + */ +void +InitProcessGlobals(void) +{ + MyProcPid = getpid(); + MyStartTimestamp = GetCurrentTimestamp(); + MyStartTime = timestamptz_to_time_t(MyStartTimestamp); + + /* + * Don't want backend to be able to see the postmaster random number + * generator state. We have to clobber the static random_seed. + */ +#ifndef HAVE_STRONG_RANDOM + random_seed = 0; + random_start_time.tv_usec = 0; +#endif + + /* Set a different seed for random() in every backend. */ + srandom((unsigned int) MyProcPid ^ (unsigned int) MyStartTimestamp); +} + + /* * reset_shared -- reset shared memory and semaphores */ @@ -4154,10 +4171,6 @@ BackendInitialize(Port *port) /* This flag will remain set until InitPostgres finishes authentication */ ClientAuthInProgress = true; /* limit visibility of log messages */ - /* save process start time */ - port->SessionStartTime = GetCurrentTimestamp(); - MyStartTime = timestamptz_to_time_t(port->SessionStartTime); - /* set these to empty in case they are needed before we set them up */ port->remote_host = ""; port->remote_port = ""; @@ -4315,23 +4328,8 @@ BackendRun(Port *port) char **av; int maxac; int ac; - long secs; - int usecs; int i; - /* - * Don't want backend to be able to see the postmaster random number - * generator state. We have to clobber the static random_seed *and* start - * a new random sequence in the random() library function. - */ -#ifndef HAVE_STRONG_RANDOM - random_seed = 0; - random_start_time.tv_usec = 0; -#endif - /* slightly hacky way to convert timestamptz into integers */ - TimestampDifference(0, port->SessionStartTime, &secs, &usecs); - srandom((unsigned int) (MyProcPid ^ (usecs << 12) ^ secs)); - /* * Now, build the argv vector that will be given to PostgresMain. * diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c index e4c6e3d406..6e13d14fcd 100644 --- a/src/backend/tcop/postgres.c +++ b/src/backend/tcop/postgres.c @@ -4632,7 +4632,7 @@ log_disconnections(int code, Datum arg) minutes, seconds; - TimestampDifference(port->SessionStartTime, + TimestampDifference(MyStartTimestamp, GetCurrentTimestamp(), &secs, &usecs); msecs = usecs / 1000; diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c index 5971310aab..c6939779b9 100644 --- a/src/backend/utils/init/globals.c +++ b/src/backend/utils/init/globals.c @@ -39,6 +39,7 @@ volatile uint32 CritSectionCount = 0; int MyProcPid; pg_time_t MyStartTime; +TimestampTz MyStartTimestamp; struct Port *MyProcPort; int32 MyCancelKey; int MyPMChildSlot; diff --git a/src/backend/utils/init/miscinit.c b/src/backend/utils/init/miscinit.c index f590ecb25e..238fe1deec 100644 --- a/src/backend/utils/init/miscinit.c +++ b/src/backend/utils/init/miscinit.c @@ -274,9 +274,7 @@ InitPostmasterChild(void) { IsUnderPostmaster = true; /* we are a postmaster subprocess now */ - MyProcPid = getpid(); /* reset MyProcPid */ - - MyStartTime = time(NULL); /* set our start time in case we call elog */ + InitProcessGlobals(); /* * make sure stderr is in binary mode before anything can possibly be @@ -321,17 +319,7 @@ InitStandaloneProcess(const char *argv0) { Assert(!IsPostmasterEnvironment); - MyProcPid = getpid(); /* reset MyProcPid */ - - MyStartTime = time(NULL); /* set our start time in case we call elog */ - - /* - * Initialize random() for the first time, like PostmasterMain() would. - * In a regular IsUnderPostmaster backend, BackendRun() computes a - * high-entropy seed before any user query. Fewer distinct initial seeds - * can occur here. - */ - srandom((unsigned int) (MyProcPid ^ MyStartTime)); + InitProcessGlobals(); /* Initialize process-local latch support */ InitializeLatchSupport(); diff --git a/src/include/libpq/libpq-be.h b/src/include/libpq/libpq-be.h index eb8bba4ed8..b2c59df54e 100644 --- a/src/include/libpq/libpq-be.h +++ b/src/include/libpq/libpq-be.h @@ -150,13 +150,6 @@ typedef struct Port */ HbaLine *hba; - /* - * Information that really has no business at all being in struct Port, - * but since it gets used by elog.c in the same way as database_name and - * other members of this struct, we may as well keep it here. - */ - TimestampTz SessionStartTime; /* backend start time */ - /* * TCP keepalive settings. * diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h index 69f356f8cd..d6b32c070c 100644 --- a/src/include/miscadmin.h +++ b/src/include/miscadmin.h @@ -25,6 +25,7 @@ #include +#include "datatype/timestamp.h" /* for TimestampTZ */ #include "pgtime.h" /* for pg_time_t */ @@ -163,6 +164,7 @@ extern PGDLLIMPORT int max_parallel_workers; extern PGDLLIMPORT int MyProcPid; extern PGDLLIMPORT pg_time_t MyStartTime; +extern PGDLLIMPORT TimestampTz MyStartTimestamp; extern PGDLLIMPORT struct Port *MyProcPort; extern PGDLLIMPORT struct Latch *MyLatch; extern int32 MyCancelKey; diff --git a/src/include/postmaster/postmaster.h b/src/include/postmaster/postmaster.h index 1877eef239..a40d66e890 100644 --- a/src/include/postmaster/postmaster.h +++ b/src/include/postmaster/postmaster.h @@ -48,6 +48,7 @@ extern PGDLLIMPORT const char *progname; extern void PostmasterMain(int argc, char *argv[]) pg_attribute_noreturn(); extern void ClosePostmasterPorts(bool am_syslogger); +extern void InitProcessGlobals(void); extern int MaxLivePostmasterChildren(void); -- 2.40.0