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Use data directory inode number, not port, to select SysV resource keys.

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This approach provides a much tighter binding between a data directory
and the associated SysV shared memory block (and SysV or named-POSIX
semaphores, if we're using those).  Key collisions are still possible,
but only between data directories stored on different filesystems,
so the situation should be negligible in practice.  More importantly,
restarting the postmaster with a different port number no longer
risks failing to identify a relevant shared memory block, even when
postmaster.pid has been removed.  A standalone backend is likewise
much more certain to detect conflicting leftover backends.

(In the longer term, we might now think about deprecating the port as
a cluster-wide value, so that one postmaster could support sockets
with varying port numbers.  But that's for another day.)

The hazards fixed here apply only on Unix systems; our Windows code
paths already use identifiers derived from the data directory path
name rather than the port.

src/test/recovery/t/017_shm.pl, which intends to test key-collision
cases, has been substantially rewritten since it can no longer use
two postmasters with identical port numbers to trigger the case.
Instead, use Perl's IPC::SharedMem module to create a conflicting
shmem segment directly.  The test script will be skipped if that
module is not available.  (This means that some older buildfarm
members won't run it, but I don't think that that results in any
meaningful coverage loss.)

Patch by me; thanks to Noah Misch and Peter Eisentraut for discussion
and review.

Discussion: https://postgr.es/m/16908.1557521200@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2019-09-05 13:31:41 -04:00
parent 8b94dab066
commit 7de19fbc0b
12 changed files with 160 additions and 125 deletions
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25
src/backend/postmaster/postmaster.c
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@@ -385,7 +385,7 @@ static void getInstallationPaths(const char *argv0);
static void checkControlFile(void);
static Port *ConnCreate(int serverFd);
static void ConnFree(Port *port);
static void reset_shared(int port);
static void reset_shared(void);
static void SIGHUP_handler(SIGNAL_ARGS);
static void pmdie(SIGNAL_ARGS);
static void reaper(SIGNAL_ARGS);
@@ -1175,7 +1175,7 @@ PostmasterMain(int argc, char *argv[])
/*
* Set up shared memory and semaphores.
*/
reset_shared(PostPortNumber);
reset_shared();
/*
* Estimate number of openable files. This must happen after setting up
@@ -2599,17 +2599,16 @@ InitProcessGlobals(void)
* reset_shared -- reset shared memory and semaphores
*/
static void
reset_shared(int port)
reset_shared(void)
{
/*
* Create or re-create shared memory and semaphores.
*
* Note: in each "cycle of life" we will normally assign the same IPC keys
* (if using SysV shmem and/or semas), since the port number is used to
* determine IPC keys. This helps ensure that we will clean up dead IPC
* objects if the postmaster crashes and is restarted.
* (if using SysV shmem and/or semas). This helps ensure that we will
* clean up dead IPC objects if the postmaster crashes and is restarted.
*/
CreateSharedMemoryAndSemaphores(port);
CreateSharedMemoryAndSemaphores();
}
@@ -3934,7 +3933,7 @@ PostmasterStateMachine(void)
/* re-read control file into local memory */
LocalProcessControlFile(true);
reset_shared(PostPortNumber);
reset_shared();
StartupPID = StartupDataBase();
Assert(StartupPID != 0);
@@ -4962,7 +4961,7 @@ SubPostmasterMain(int argc, char *argv[])
InitProcess();
/* Attach process to shared data structures */
CreateSharedMemoryAndSemaphores(0);
CreateSharedMemoryAndSemaphores();
/* And run the backend */
BackendRun(&port); /* does not return */
@@ -4976,7 +4975,7 @@ SubPostmasterMain(int argc, char *argv[])
InitAuxiliaryProcess();
/* Attach process to shared data structures */
CreateSharedMemoryAndSemaphores(0);
CreateSharedMemoryAndSemaphores();
AuxiliaryProcessMain(argc - 2, argv + 2); /* does not return */
}
@@ -4989,7 +4988,7 @@ SubPostmasterMain(int argc, char *argv[])
InitProcess();
/* Attach process to shared data structures */
CreateSharedMemoryAndSemaphores(0);
CreateSharedMemoryAndSemaphores();
AutoVacLauncherMain(argc - 2, argv + 2); /* does not return */
}
@@ -5002,7 +5001,7 @@ SubPostmasterMain(int argc, char *argv[])
InitProcess();
/* Attach process to shared data structures */
CreateSharedMemoryAndSemaphores(0);
CreateSharedMemoryAndSemaphores();
AutoVacWorkerMain(argc - 2, argv + 2); /* does not return */
}
@@ -5020,7 +5019,7 @@ SubPostmasterMain(int argc, char *argv[])
InitProcess();
/* Attach process to shared data structures */
CreateSharedMemoryAndSemaphores(0);
CreateSharedMemoryAndSemaphores();
/* Fetch MyBgworkerEntry from shared memory */
shmem_slot = atoi(argv[1] + 15);