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Prevent freshly-started backend from ignoring SIGUSR1, per race condition

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observed by Inoue.  Also, don't call ProcRemove() from postmaster if we
have detected a backend crash --- too risky if shared memory is corrupted.
It's not needed anyway, considering we are going to reinitialize shared
memory and semaphores as soon as the last child is dead.
REL7_1_STABLE
Tom Lane 25 years ago
parent e4d97cb70e
commit 39b547f430
2 changed files with 74 additions and 63 deletions
Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL
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  1. 105
      src/backend/postmaster/postmaster.c
  2. 32
      src/backend/tcop/postgres.c

105
src/backend/postmaster/postmaster.c
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@ -11,7 +11,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/postmaster/postmaster.c,v 1.200 2000/12/18 18:45:04 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/postmaster/postmaster.c,v 1.201 2000/12/20 21:51:52 tgl Exp $
*
* NOTES
*
@ -180,7 +180,7 @@ static time_t checkpointed = 0;
static int Shutdown = NoShutdown;
static bool FatalError = false;
static bool FatalError = false; /* T if recovering from backend crash */
/*
* State for assigning random salts and cancel keys.
@ -649,7 +649,7 @@ PostmasterMain(int argc, char *argv[])
pqsignal(SIGTERM, pmdie); /* wait for children and ShutdownDataBase */
pqsignal(SIGALRM, SIG_IGN); /* ignored */
pqsignal(SIGPIPE, SIG_IGN); /* ignored */
pqsignal(SIGUSR1, SIG_IGN); /* ignored */
pqsignal(SIGUSR1, pmdie); /* currently ignored, but see note in pmdie */
pqsignal(SIGUSR2, pmdie); /* send SIGUSR2, don't die */
pqsignal(SIGCHLD, reaper); /* handle child termination */
pqsignal(SIGTTIN, SIG_IGN); /* ignored */
@ -1329,6 +1329,18 @@ pmdie(SIGNAL_ARGS)
switch (postgres_signal_arg)
{
case SIGUSR1:
/*
* Currently the postmaster ignores SIGUSR1 (maybe it should
* do something useful instead?) But we must have some handler
* installed for SIGUSR1, not just set it to SIG_IGN. Else, a
* freshly spawned backend would likewise have it set to SIG_IGN,
* which would mean the backend would ignore any attempt to kill
* it before it had gotten as far as setting up its own handler.
*/
errno = save_errno;
return;
case SIGUSR2:
/*
@ -1511,7 +1523,7 @@ reaper(SIGNAL_ARGS)
ExitPostmaster(1);
}
StartupPID = 0;
FatalError = false;
FatalError = false; /* done with recovery */
if (Shutdown > NoShutdown)
{
if (ShutdownPID > 0)
@ -1539,12 +1551,7 @@ reaper(SIGNAL_ARGS)
/*
* Wait for all children exit, then reset shmem and StartupDataBase.
*/
if (DLGetHead(BackendList))
{
errno = save_errno;
return;
}
if (StartupPID > 0 || ShutdownPID > 0)
if (DLGetHead(BackendList) || StartupPID > 0 || ShutdownPID > 0)
{
errno = save_errno;
return;
@ -1595,13 +1602,10 @@ CleanupProc(int pid,
Dlelem *curr,
*next;
Backend *bp;
int sig;
if (DebugLvl)
{
fprintf(stderr, "%s: CleanupProc: pid %d exited with status %d\n",
progname, pid, exitstatus);
}
/*
* If a backend dies in an ugly way (i.e. exit status not 0) then we
@ -1609,7 +1613,7 @@ CleanupProc(int pid,
* we assume everything is hunky dory and simply remove the backend
* from the active backend list.
*/
if (!exitstatus)
if (exitstatus == 0)
{
curr = DLGetHead(BackendList);
while (curr)
@ -1628,66 +1632,64 @@ CleanupProc(int pid,
if (pid == CheckPointPID)
{
CheckPointPID = 0;
checkpointed = time(NULL);
if (!FatalError)
checkpointed = time(NULL);
}
else
ProcRemove(pid);
{
/* Why is this done here, and not by the backend itself? */
if (!FatalError)
ProcRemove(pid);
}
return;
}
if (!FatalError)
{
/* Make log entry unless we did so already */
tnow = time(NULL);
fprintf(stderr, "Server process (pid %d) exited with status %d at %s"
"Terminating any active server processes...\n",
pid, exitstatus, ctime(&tnow));
fflush(stderr);
}
FatalError = true;
curr = DLGetHead(BackendList);
while (curr)
{
next = DLGetSucc(curr);
bp = (Backend *) DLE_VAL(curr);
/*
* SIGUSR1 is the special signal that says exit without proc_exit
* and let the user know what's going on. ProcSemaphoreKill()
* cleans up the backends semaphore. If SendStop is set (-s on
* command line), then we send a SIGSTOP so that we can core dumps
* from all backends by hand.
*/
sig = (SendStop) ? SIGSTOP : SIGUSR1;
if (bp->pid != pid)
{
if (DebugLvl)
fprintf(stderr, "%s: CleanupProc: sending %s to process %d\n",
progname,
(sig == SIGUSR1)
? "SIGUSR1" : "SIGSTOP",
bp->pid);
kill(bp->pid, sig);
/*
* This backend is still alive. Unless we did so already,
* tell it to commit hara-kiri.
*
* SIGUSR1 is the special signal that says exit without proc_exit
* and let the user know what's going on. But if SendStop is set
* (-s on command line), then we send SIGSTOP instead, so that we
* can get core dumps from all backends by hand.
*/
if (!FatalError)
{
if (DebugLvl)
fprintf(stderr, "%s: CleanupProc: sending %s to process %d\n",
progname,
(SendStop ? "SIGSTOP" : "SIGUSR1"),
bp->pid);
kill(bp->pid, (SendStop ? SIGSTOP : SIGUSR1));
}
}
else
{
/*
* I don't like that we call ProcRemove() here, assuming that
* shmem may be corrupted! But is there another way to free
* backend semaphores? Actually, I believe that we need not in
* per backend semaphore at all (we use them to wait on lock
* only, couldn't we just sigpause?), so probably we'll remove
* this call from here someday. -- vadim 04-10-1999
* Found entry for freshly-dead backend, so remove it.
*
* Don't call ProcRemove() here, since shmem may be corrupted!
* We are going to reinitialize shmem and semaphores anyway
* once all the children are dead, so no need for it.
*/
if (pid == CheckPointPID)
{
CheckPointPID = 0;
checkpointed = 0;
}
else
ProcRemove(pid);
DLRemove(curr);
free(bp);
DLFreeElem(curr);
@ -1695,6 +1697,13 @@ CleanupProc(int pid,
curr = next;
}
if (pid == CheckPointPID)
{
CheckPointPID = 0;
checkpointed = 0;
}
FatalError = true;
}
/*

32
src/backend/tcop/postgres.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/tcop/postgres.c,v 1.197 2000/12/18 18:45:05 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/tcop/postgres.c,v 1.198 2000/12/20 21:51:52 tgl Exp $
*
* NOTES
* this is the "main" module of the postgres backend and
@ -1462,21 +1462,12 @@ PostgresMain(int argc, char *argv[], int real_argc, char *real_argv[], const cha
Assert(DataDir);
/*
* 1. Set BlockSig and UnBlockSig masks. 2. Set up signal handlers. 3.
* Allow only SIGUSR1 signal (we never block it) during
* initialization.
* Set up signal handlers and masks.
*
* Note that postmaster already blocked ALL signals to make us happy.
* Note that postmaster blocked all signals before forking child process,
* so there is no race condition whereby we might receive a signal before
* we have set up the handler.
*/
pqinitmask();
#ifdef HAVE_SIGPROCMASK
sigdelset(&BlockSig, SIGUSR1);
#else
BlockSig &= ~(sigmask(SIGUSR1));
#endif
PG_SETMASK(&BlockSig); /* block everything except SIGUSR1 */
pqsignal(SIGHUP, SigHupHandler); /* set flag to read config file */
pqsignal(SIGINT, QueryCancelHandler); /* cancel current query */
@ -1499,6 +1490,17 @@ PostgresMain(int argc, char *argv[], int real_argc, char *real_argv[], const cha
pqsignal(SIGTTOU, SIG_DFL);
pqsignal(SIGCONT, SIG_DFL);
pqinitmask();
/* We allow SIGUSR1 (quickdie) at all times */
#ifdef HAVE_SIGPROCMASK
sigdelset(&BlockSig, SIGUSR1);
#else
BlockSig &= ~(sigmask(SIGUSR1));
#endif
PG_SETMASK(&BlockSig); /* block everything except SIGUSR1 */
if (IsUnderPostmaster)
{
@ -1649,7 +1651,7 @@ PostgresMain(int argc, char *argv[], int real_argc, char *real_argv[], const cha
if (!IsUnderPostmaster)
{
puts("\nPOSTGRES backend interactive interface ");
puts("$Revision: 1.197 $ $Date: 2000/12/18 18:45:05 $\n");
puts("$Revision: 1.198 $ $Date: 2000/12/20 21:51:52 $\n");
}
/*

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