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postgresql/src/backend/port/win32_shmem.c

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/*-------------------------------------------------------------------------
*
* win32_shmem.c
* Implement shared memory using win32 facilities
*
* Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
*
* IDENTIFICATION
* src/backend/port/win32_shmem.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "miscadmin.h"
#include "storage/dsm.h"
#include "storage/ipc.h"
#include "storage/pg_shmem.h"
#include "utils/guc_hooks.h"
/*
* Early in a process's life, Windows asynchronously creates threads for the
* process's "default thread pool"
* (https://docs.microsoft.com/en-us/windows/desktop/ProcThread/thread-pools).
* Occasionally, thread creation allocates a stack after
* PGSharedMemoryReAttach() has released UsedShmemSegAddr and before it has
* mapped shared memory at UsedShmemSegAddr. This would cause mapping to fail
* if the allocator preferred the just-released region for allocating the new
* thread stack. We observed such failures in some Windows Server 2016
* configurations. To give the system another region to prefer, reserve and
* release an additional, protective region immediately before reserving or
* releasing shared memory. The idea is that, if the allocator handed out
* REGION1 pages before REGION2 pages at one occasion, it will do so whenever
* both regions are free. Windows Server 2016 exhibits that behavior, and a
* system behaving differently would have less need to protect
* UsedShmemSegAddr. The protective region must be at least large enough for
* one thread stack. However, ten times as much is less than 2% of the 32-bit
* address space and is negligible relative to the 64-bit address space.
*/
#define PROTECTIVE_REGION_SIZE (10 * WIN32_STACK_RLIMIT)
void *ShmemProtectiveRegion = NULL;
HANDLE UsedShmemSegID = INVALID_HANDLE_VALUE;
void *UsedShmemSegAddr = NULL;
static Size UsedShmemSegSize = 0;
static bool EnableLockPagesPrivilege(int elevel);
static void pgwin32_SharedMemoryDelete(int status, Datum shmId);
/*
* Generate shared memory segment name. Expand the data directory, to generate
* an identifier unique for this data directory. Then replace all backslashes
* with forward slashes, since backslashes aren't permitted in global object names.
*
* Store the shared memory segment in the Global\ namespace (requires NT2 TSE or
* 2000, but that's all we support for other reasons as well), to make sure you can't
* open two postmasters in different sessions against the same data directory.
*
* XXX: What happens with junctions? It's only someone breaking things on purpose,
* and this is still better than before, but we might want to do something about
* that sometime in the future.
*/
static char *
GetSharedMemName(void)
{
char *retptr;
DWORD bufsize;
DWORD r;
char *cp;
bufsize = GetFullPathName(DataDir, 0, NULL, NULL);
if (bufsize == 0)
elog(FATAL, "could not get size for full pathname of datadir %s: error code %lu",
DataDir, GetLastError());
retptr = malloc(bufsize + 18); /* 18 for Global\PostgreSQL: */
if (retptr == NULL)
elog(FATAL, "could not allocate memory for shared memory name");
strcpy(retptr, "Global\\PostgreSQL:");
r = GetFullPathName(DataDir, bufsize, retptr + 18, NULL);
if (r == 0 || r > bufsize)
elog(FATAL, "could not generate full pathname for datadir %s: error code %lu",
DataDir, GetLastError());
/*
* XXX: Intentionally overwriting the Global\ part here. This was not the
* original approach, but putting it in the actual Global\ namespace
* causes permission errors in a lot of cases, so we leave it in the
* default namespace for now.
*/
for (cp = retptr; *cp; cp++)
if (*cp == '\\')
*cp = '/';
return retptr;
}
/*
* PGSharedMemoryIsInUse
*
* Is a previously-existing shmem segment still existing and in use?
*
* The point of this exercise is to detect the case where a prior postmaster
* crashed, but it left child backends that are still running. Therefore
* we only care about shmem segments that are associated with the intended
* DataDir. This is an important consideration since accidental matches of
* shmem segment IDs are reasonably common.
*/
bool
PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
{
char *szShareMem;
HANDLE hmap;
szShareMem = GetSharedMemName();
hmap = OpenFileMapping(FILE_MAP_READ, FALSE, szShareMem);
free(szShareMem);
if (hmap == NULL)
return false;
CloseHandle(hmap);
return true;
}
/*
* EnableLockPagesPrivilege
*
* Try to acquire SeLockMemoryPrivilege so we can use large pages.
*/
static bool
EnableLockPagesPrivilege(int elevel)
{
HANDLE hToken;
TOKEN_PRIVILEGES tp;
LUID luid;
if (!OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, &hToken))
{
ereport(elevel,
(errmsg("could not enable user right \"%s\": error code %lu",
/*
* translator: This is a term from Windows and should be translated to
* match the Windows localization.
*/
_("Lock pages in memory"),
GetLastError()),
errdetail("Failed system call was %s.", "OpenProcessToken")));
return FALSE;
}
if (!LookupPrivilegeValue(NULL, SE_LOCK_MEMORY_NAME, &luid))
{
ereport(elevel,
(errmsg("could not enable user right \"%s\": error code %lu", _("Lock pages in memory"), GetLastError()),
errdetail("Failed system call was %s.", "LookupPrivilegeValue")));
CloseHandle(hToken);
return FALSE;
}
tp.PrivilegeCount = 1;
tp.Privileges[0].Luid = luid;
tp.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;
if (!AdjustTokenPrivileges(hToken, FALSE, &tp, 0, NULL, NULL))
{
ereport(elevel,
(errmsg("could not enable user right \"%s\": error code %lu", _("Lock pages in memory"), GetLastError()),
errdetail("Failed system call was %s.", "AdjustTokenPrivileges")));
CloseHandle(hToken);
return FALSE;
}
if (GetLastError() != ERROR_SUCCESS)
{
if (GetLastError() == ERROR_NOT_ALL_ASSIGNED)
ereport(elevel,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("could not enable user right \"%s\"", _("Lock pages in memory")),
errhint("Assign user right \"%s\" to the Windows user account which runs PostgreSQL.",
_("Lock pages in memory"))));
else
ereport(elevel,
(errmsg("could not enable user right \"%s\": error code %lu", _("Lock pages in memory"), GetLastError()),
errdetail("Failed system call was %s.", "AdjustTokenPrivileges")));
CloseHandle(hToken);
return FALSE;
}
CloseHandle(hToken);
return TRUE;
}
/*
* PGSharedMemoryCreate
*
* Create a shared memory segment of the given size and initialize its
* standard header.
*/
PGShmemHeader *
PGSharedMemoryCreate(Size size,
PGShmemHeader **shim)
{
void *memAddress;
PGShmemHeader *hdr;
HANDLE hmap,
hmap2;
char *szShareMem;
int i;
DWORD size_high;
DWORD size_low;
SIZE_T largePageSize = 0;
Size orig_size = size;
DWORD flProtect = PAGE_READWRITE;
DWORD desiredAccess;
ShmemProtectiveRegion = VirtualAlloc(NULL, PROTECTIVE_REGION_SIZE,
MEM_RESERVE, PAGE_NOACCESS);
if (ShmemProtectiveRegion == NULL)
elog(FATAL, "could not reserve memory region: error code %lu",
GetLastError());
/* Room for a header? */
Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
szShareMem = GetSharedMemName();
UsedShmemSegAddr = NULL;
if (huge_pages == HUGE_PAGES_ON || huge_pages == HUGE_PAGES_TRY)
{
/* Does the processor support large pages? */
largePageSize = GetLargePageMinimum();
if (largePageSize == 0)
{
ereport(huge_pages == HUGE_PAGES_ON ? FATAL : DEBUG1,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("the processor does not support large pages")));
ereport(DEBUG1,
(errmsg_internal("disabling huge pages")));
}
else if (!EnableLockPagesPrivilege(huge_pages == HUGE_PAGES_ON ? FATAL : DEBUG1))
{
ereport(DEBUG1,
(errmsg_internal("disabling huge pages")));
}
else
{
/* Huge pages available and privilege enabled, so turn on */
flProtect = PAGE_READWRITE | SEC_COMMIT | SEC_LARGE_PAGES;
/* Round size up as appropriate. */
if (size % largePageSize != 0)
size += largePageSize - (size % largePageSize);
}
}
retry:
#ifdef _WIN64
size_high = size >> 32;
#else
size_high = 0;
#endif
size_low = (DWORD) size;
/*
* When recycling a shared memory segment, it may take a short while
* before it gets dropped from the global namespace. So re-try after
* sleeping for a second, and continue retrying 10 times. (both the 1
* second time and the 10 retries are completely arbitrary)
*/
for (i = 0; i < 10; i++)
{
/*
* In case CreateFileMapping() doesn't set the error code to 0 on
* success
*/
SetLastError(0);
hmap = CreateFileMapping(INVALID_HANDLE_VALUE, /* Use the pagefile */
NULL, /* Default security attrs */
flProtect,
size_high, /* Size Upper 32 Bits */
size_low, /* Size Lower 32 bits */
szShareMem);
if (!hmap)
{
if (GetLastError() == ERROR_NO_SYSTEM_RESOURCES &&
huge_pages == HUGE_PAGES_TRY &&
(flProtect & SEC_LARGE_PAGES) != 0)
{
elog(DEBUG1, "CreateFileMapping(%zu) with SEC_LARGE_PAGES failed, "
"huge pages disabled",
size);
/*
* Use the original size, not the rounded-up value, when
* falling back to non-huge pages.
*/
size = orig_size;
flProtect = PAGE_READWRITE;
goto retry;
}
else
ereport(FATAL,
(errmsg("could not create shared memory segment: error code %lu", GetLastError()),
errdetail("Failed system call was CreateFileMapping(size=%zu, name=%s).",
size, szShareMem)));
}
/*
* If the segment already existed, CreateFileMapping() will return a
* handle to the existing one and set ERROR_ALREADY_EXISTS.
*/
if (GetLastError() == ERROR_ALREADY_EXISTS)
{
CloseHandle(hmap); /* Close the handle, since we got a valid one
* to the previous segment. */
hmap = NULL;
Sleep(1000);
continue;
}
break;
}
/*
* If the last call in the loop still returned ERROR_ALREADY_EXISTS, this
* shared memory segment exists and we assume it belongs to somebody else.
*/
if (!hmap)
ereport(FATAL,
(errmsg("pre-existing shared memory block is still in use"),
errhint("Check if there are any old server processes still running, and terminate them.")));
free(szShareMem);
/*
* Make the handle inheritable
*/
if (!DuplicateHandle(GetCurrentProcess(), hmap, GetCurrentProcess(), &hmap2, 0, TRUE, DUPLICATE_SAME_ACCESS))
ereport(FATAL,
(errmsg("could not create shared memory segment: error code %lu", GetLastError()),
errdetail("Failed system call was DuplicateHandle.")));
/*
* Close the old, non-inheritable handle. If this fails we don't really
* care.
*/
if (!CloseHandle(hmap))
elog(LOG, "could not close handle to shared memory: error code %lu", GetLastError());
desiredAccess = FILE_MAP_WRITE | FILE_MAP_READ;
#ifdef FILE_MAP_LARGE_PAGES
/* Set large pages if wanted. */
if ((flProtect & SEC_LARGE_PAGES) != 0)
desiredAccess |= FILE_MAP_LARGE_PAGES;
#endif
/*
* Get a pointer to the new shared memory segment. Map the whole segment
* at once, and let the system decide on the initial address.
*/
memAddress = MapViewOfFileEx(hmap2, desiredAccess, 0, 0, 0, NULL);
if (!memAddress)
ereport(FATAL,
(errmsg("could not create shared memory segment: error code %lu", GetLastError()),
errdetail("Failed system call was MapViewOfFileEx.")));
/*
* OK, we created a new segment. Mark it as created by this process. The
* order of assignments here is critical so that another Postgres process
* can't see the header as valid but belonging to an invalid PID!
*/
hdr = (PGShmemHeader *) memAddress;
hdr->creatorPID = getpid();
hdr->magic = PGShmemMagic;
/*
* Initialize space allocation status for segment.
*/
hdr->totalsize = size;
hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
hdr->dsm_control = 0;
/* Save info for possible future use */
UsedShmemSegAddr = memAddress;
UsedShmemSegSize = size;
UsedShmemSegID = hmap2;
/* Register on-exit routine to delete the new segment */
on_shmem_exit(pgwin32_SharedMemoryDelete, PointerGetDatum(hmap2));
*shim = hdr;
/* Report whether huge pages are in use */
SetConfigOption("huge_pages_status", (flProtect & SEC_LARGE_PAGES) ?
"on" : "off", PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
return hdr;
}
/*
* PGSharedMemoryReAttach
*
* This is called during startup of a postmaster child process to re-attach to
* an already existing shared memory segment, using the handle inherited from
* the postmaster.
*
* ShmemProtectiveRegion, UsedShmemSegID and UsedShmemSegAddr are implicit
* parameters to this routine. The caller must have already restored them to
* the postmaster's values.
*/
void
PGSharedMemoryReAttach(void)
{
PGShmemHeader *hdr;
void *origUsedShmemSegAddr = UsedShmemSegAddr;
Assert(ShmemProtectiveRegion != NULL);
Assert(UsedShmemSegAddr != NULL);
Assert(IsUnderPostmaster);
/*
* Release memory region reservations made by the postmaster
*/
if (VirtualFree(ShmemProtectiveRegion, 0, MEM_RELEASE) == 0)
elog(FATAL, "failed to release reserved memory region (addr=%p): error code %lu",
ShmemProtectiveRegion, GetLastError());
if (VirtualFree(UsedShmemSegAddr, 0, MEM_RELEASE) == 0)
elog(FATAL, "failed to release reserved memory region (addr=%p): error code %lu",
UsedShmemSegAddr, GetLastError());
hdr = (PGShmemHeader *) MapViewOfFileEx(UsedShmemSegID, FILE_MAP_READ | FILE_MAP_WRITE, 0, 0, 0, UsedShmemSegAddr);
if (!hdr)
elog(FATAL, "could not reattach to shared memory (key=%p, addr=%p): error code %lu",
UsedShmemSegID, UsedShmemSegAddr, GetLastError());
if (hdr != origUsedShmemSegAddr)
elog(FATAL, "reattaching to shared memory returned unexpected address (got %p, expected %p)",
hdr, origUsedShmemSegAddr);
if (hdr->magic != PGShmemMagic)
elog(FATAL, "reattaching to shared memory returned non-PostgreSQL memory");
dsm_set_control_handle(hdr->dsm_control);
UsedShmemSegAddr = hdr; /* probably redundant */
}
/*
* PGSharedMemoryNoReAttach
*
* This is called during startup of a postmaster child process when we choose
* *not* to re-attach to the existing shared memory segment. We must clean up
* to leave things in the appropriate state.
*
* The child process startup logic might or might not call PGSharedMemoryDetach
* after this; make sure that it will be a no-op if called.
*
* ShmemProtectiveRegion, UsedShmemSegID and UsedShmemSegAddr are implicit
* parameters to this routine. The caller must have already restored them to
* the postmaster's values.
*/
void
PGSharedMemoryNoReAttach(void)
{
Assert(ShmemProtectiveRegion != NULL);
Assert(UsedShmemSegAddr != NULL);
Assert(IsUnderPostmaster);
/*
* Under Windows we will not have mapped the segment, so we don't need to
* un-map it. Just reset UsedShmemSegAddr to show we're not attached.
*/
UsedShmemSegAddr = NULL;
/*
* We *must* close the inherited shmem segment handle, else Windows will
* consider the existence of this process to mean it can't release the
* shmem segment yet. We can now use PGSharedMemoryDetach to do that.
*/
PGSharedMemoryDetach();
}
/*
* PGSharedMemoryDetach
*
* Detach from the shared memory segment, if still attached. This is not
* intended to be called explicitly by the process that originally created the
* segment (it will have an on_shmem_exit callback registered to do that).
* Rather, this is for subprocesses that have inherited an attachment and want
* to get rid of it.
*
* ShmemProtectiveRegion, UsedShmemSegID and UsedShmemSegAddr are implicit
* parameters to this routine.
*/
void
PGSharedMemoryDetach(void)
{
/*
* Releasing the protective region liberates an unimportant quantity of
* address space, but be tidy.
*/
if (ShmemProtectiveRegion != NULL)
{
if (VirtualFree(ShmemProtectiveRegion, 0, MEM_RELEASE) == 0)
elog(LOG, "failed to release reserved memory region (addr=%p): error code %lu",
ShmemProtectiveRegion, GetLastError());
ShmemProtectiveRegion = NULL;
}
/* Unmap the view, if it's mapped */
if (UsedShmemSegAddr != NULL)
{
if (!UnmapViewOfFile(UsedShmemSegAddr))
elog(LOG, "could not unmap view of shared memory: error code %lu",
GetLastError());
UsedShmemSegAddr = NULL;
}
/* And close the shmem handle, if we have one */
if (UsedShmemSegID != INVALID_HANDLE_VALUE)
{
if (!CloseHandle(UsedShmemSegID))
elog(LOG, "could not close handle to shared memory: error code %lu",
GetLastError());
UsedShmemSegID = INVALID_HANDLE_VALUE;
}
}
/*
* pgwin32_SharedMemoryDelete
*
* Detach from and delete the shared memory segment
* (called as an on_shmem_exit callback, hence funny argument list)
*/
static void
pgwin32_SharedMemoryDelete(int status, Datum shmId)
{
Assert(DatumGetPointer(shmId) == UsedShmemSegID);
PGSharedMemoryDetach();
}
/*
* pgwin32_ReserveSharedMemoryRegion(hChild)
*
* Reserve the memory region that will be used for shared memory in a child
* process. It is called before the child process starts, to make sure the
* memory is available.
*
* Once the child starts, DLLs loading in different order or threads getting
* scheduled differently may allocate memory which can conflict with the
* address space we need for our shared memory. By reserving the shared
* memory region before the child starts, and freeing it only just before we
* attempt to get access to the shared memory forces these allocations to
* be given different address ranges that don't conflict.
*
* NOTE! This function executes in the postmaster, and should for this
* reason not use elog(FATAL) since that would take down the postmaster.
*/
int
pgwin32_ReserveSharedMemoryRegion(HANDLE hChild)
{
void *address;
Assert(ShmemProtectiveRegion != NULL);
Assert(UsedShmemSegAddr != NULL);
Assert(UsedShmemSegSize != 0);
/* ShmemProtectiveRegion */
address = VirtualAllocEx(hChild, ShmemProtectiveRegion,
PROTECTIVE_REGION_SIZE,
MEM_RESERVE, PAGE_NOACCESS);
if (address == NULL)
{
/* Don't use FATAL since we're running in the postmaster */
elog(LOG, "could not reserve shared memory region (addr=%p) for child %p: error code %lu",
ShmemProtectiveRegion, hChild, GetLastError());
return false;
}
if (address != ShmemProtectiveRegion)
{
/*
* Should never happen - in theory if allocation granularity causes
* strange effects it could, so check just in case.
*
* Don't use FATAL since we're running in the postmaster.
*/
elog(LOG, "reserved shared memory region got incorrect address %p, expected %p",
address, ShmemProtectiveRegion);
return false;
}
/* UsedShmemSegAddr */
address = VirtualAllocEx(hChild, UsedShmemSegAddr, UsedShmemSegSize,
MEM_RESERVE, PAGE_READWRITE);
if (address == NULL)
{
elog(LOG, "could not reserve shared memory region (addr=%p) for child %p: error code %lu",
UsedShmemSegAddr, hChild, GetLastError());
return false;
}
if (address != UsedShmemSegAddr)
{
elog(LOG, "reserved shared memory region got incorrect address %p, expected %p",
address, UsedShmemSegAddr);
return false;
}
return true;
}
/*
* This function is provided for consistency with sysv_shmem.c and does not
* provide any useful information for Windows. To obtain the large page size,
* use GetLargePageMinimum() instead.
*/
void
GetHugePageSize(Size *hugepagesize, int *mmap_flags)
{
if (hugepagesize)
*hugepagesize = 0;
if (mmap_flags)
*mmap_flags = 0;
}
/*
* GUC check_hook for huge_page_size
*/
bool
check_huge_page_size(int *newval, void **extra, GucSource source)
{
if (*newval != 0)
{
GUC_check_errdetail("\"huge_page_size\" must be 0 on this platform.");
return false;
}
return true;
}
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