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Consistently test for in-use shared memory.

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postmaster startup scrutinizes any shared memory segment recorded in
postmaster.pid, exiting if that segment matches the current data
directory and has an attached process.  When the postmaster.pid file was
missing, a starting postmaster used weaker checks.  Change to use the
same checks in both scenarios.  This increases the chance of a startup
failure, in lieu of data corruption, if the DBA does "kill -9 `head -n1
postmaster.pid` && rm postmaster.pid && pg_ctl -w start".  A postmaster
will no longer stop if shmat() of an old segment fails with EACCES.  A
postmaster will no longer recycle segments pertaining to other data
directories.  That's good for production, but it's bad for integration
tests that crash a postmaster and immediately delete its data directory.
Such a test now leaks a segment indefinitely.  No "make check-world"
test does that.  win32_shmem.c already avoided all these problems.  In
9.6 and later, enhance PostgresNode to facilitate testing.  Back-patch
to 9.4 (all supported versions).

Reviewed (in earlier versions) by Daniel Gustafsson and Kyotaro HORIGUCHI.

Discussion: https://postgr.es/m/20190408064141.GA2016666@rfd.leadboat.com
This commit is contained in:
Noah Misch
2019-04-12 22:36:38 -07:00
parent db8db624e8
commit c098509927
11 changed files with 527 additions and 182 deletions
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14
src/backend/storage/ipc/ipci.c
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@ -89,12 +89,9 @@ RequestAddinShmemSpace(Size size)
* through the same code as before. (Note that the called routines mostly
* check IsUnderPostmaster, rather than EXEC_BACKEND, to detect this case.
* This is a bit code-wasteful and could be cleaned up.)
*
* If "makePrivate" is true then we only need private memory, not shared
* memory. This is true for a standalone backend, false for a postmaster.
*/
void
CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
CreateSharedMemoryAndSemaphores(int port)
{
PGShmemHeader *shim = NULL;
@ -166,7 +163,7 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
/*
* Create the shmem segment
*/
seghdr = PGSharedMemoryCreate(size, makePrivate, port, &shim);
seghdr = PGSharedMemoryCreate(size, port, &shim);
InitShmemAccess(seghdr);
@ -187,12 +184,9 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
{
/*
* We are reattaching to an existing shared memory segment. This
* should only be reached in the EXEC_BACKEND case, and even then only
* with makePrivate == false.
* should only be reached in the EXEC_BACKEND case.
*/
#ifdef EXEC_BACKEND
Assert(!makePrivate);
#else
#ifndef EXEC_BACKEND
elog(PANIC, "should be attached to shared memory already");
#endif
}