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* [PATCH v2] windows: Only consider us to be running as service if stderr is invalid.
@ 2021-03-03 05:24 Andres Freund <[email protected]>
0 siblings, 0 replies; 2+ messages in thread
From: Andres Freund @ 2021-03-03 05:24 UTC (permalink / raw)
Previously pgwin32_is_service() would falsely return true when
postgres is started from somewhere within a service, but not as a
service. That is e.g. always the case with windows docker containers,
which some CI services use to run windows tests in.
In addition to this change, it likely would be a good idea to have
pg_ctl runservice pass down a flag indicating that postgres is running
as a service.
Author: Andres Freund <[email protected]>
Discussion: https://postgr.es/m/[email protected]
---
src/port/win32security.c | 13 +++++++++++--
src/bin/pg_ctl/pg_ctl.c | 33 +++++++++++++++++++++++++++++++++
2 files changed, 44 insertions(+), 2 deletions(-)
diff --git a/src/port/win32security.c b/src/port/win32security.c
index 4a673fde19a..b57ce61d752 100644
--- a/src/port/win32security.c
+++ b/src/port/win32security.c
@@ -95,8 +95,9 @@ pgwin32_is_admin(void)
* We consider ourselves running as a service if one of the following is
* true:
*
- * 1) We are running as LocalSystem (only used by services)
- * 2) Our token contains SECURITY_SERVICE_RID (automatically added to the
+ * 1) Standard error is not valid (always the case for services)
+ * 2) We are running as LocalSystem (only used by services)
+ * 3) Our token contains SECURITY_SERVICE_RID (automatically added to the
* process token by the SCM when starting a service)
*
* The check for LocalSystem is needed, because surprisingly, if a service
@@ -121,11 +122,19 @@ pgwin32_is_service(void)
PSID ServiceSid;
PSID LocalSystemSid;
SID_IDENTIFIER_AUTHORITY NtAuthority = {SECURITY_NT_AUTHORITY};
+ HANDLE stderr_handle;
/* Only check the first time */
if (_is_service != -1)
return _is_service;
+ stderr_handle = GetStdHandle(STD_ERROR_HANDLE);
+ if (stderr_handle != INVALID_HANDLE_VALUE && stderr_handle != NULL)
+ {
+ _is_service = 0;
+ return _is_service;
+ }
+
/* First check for LocalSystem */
if (!AllocateAndInitializeSid(&NtAuthority, 1,
SECURITY_LOCAL_SYSTEM_RID, 0, 0, 0, 0, 0, 0, 0,
diff --git a/src/bin/pg_ctl/pg_ctl.c b/src/bin/pg_ctl/pg_ctl.c
index 7985da0a943..c99e3c507de 100644
--- a/src/bin/pg_ctl/pg_ctl.c
+++ b/src/bin/pg_ctl/pg_ctl.c
@@ -1737,6 +1737,31 @@ typedef BOOL (WINAPI * __SetInformationJobObject) (HANDLE, JOBOBJECTINFOCLASS, L
typedef BOOL (WINAPI * __AssignProcessToJobObject) (HANDLE, HANDLE);
typedef BOOL (WINAPI * __QueryInformationJobObject) (HANDLE, JOBOBJECTINFOCLASS, LPVOID, DWORD, LPDWORD);
+/*
+ * Set up STARTUPINFO for the new process to inherit this process' handles.
+ *
+ * Process started as services appear to have "empty" handles (GetStdHandle()
+ * returns NULL) rather than invalid ones. But passing down NULL ourselves
+ * doesn't work, it's interpreted as STARTUPINFO->hStd* not being set. But we
+ * can pass down INVALID_HANDLE_VALUE - which makes GetStdHandle() in the new
+ * process (and its child processes!) return INVALID_HANDLE_VALUE. Which
+ * achieves the goal of postmaster running in a similar environment as pg_ctl.
+ */
+static void
+InheritStdHandles(STARTUPINFO* si)
+{
+ si->dwFlags |= STARTF_USESTDHANDLES;
+ si->hStdInput = GetStdHandle(STD_INPUT_HANDLE);
+ if (si->hStdInput == NULL)
+ si->hStdInput = INVALID_HANDLE_VALUE;
+ si->hStdOutput = GetStdHandle(STD_OUTPUT_HANDLE);
+ if (si->hStdOutput == NULL)
+ si->hStdOutput = INVALID_HANDLE_VALUE;
+ si->hStdError = GetStdHandle(STD_ERROR_HANDLE);
+ if (si->hStdError == NULL)
+ si->hStdError = INVALID_HANDLE_VALUE;
+}
+
/*
* Create a restricted token, a job object sandbox, and execute the specified
* process with it.
@@ -1774,6 +1799,14 @@ CreateRestrictedProcess(char *cmd, PROCESS_INFORMATION *processInfo, bool as_ser
ZeroMemory(&si, sizeof(si));
si.cb = sizeof(si);
+ /*
+ * Set stdin/stdout/stderr handles to be inherited in the child
+ * process. That allows postmaster and the processes it starts to perform
+ * additional checks to see if running in a service (otherwise they get
+ * the default console handles - which point to "somewhere").
+ */
+ InheritStdHandles(&si);
+
Advapi32Handle = LoadLibrary("ADVAPI32.DLL");
if (Advapi32Handle != NULL)
{
--
2.29.2.540.g3cf59784d4
--pm3lfdw7knjptu4k--
^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: locked reads for atomics
@ 2023-11-11 02:38 Nathan Bossart <[email protected]>
0 siblings, 0 replies; 2+ messages in thread
From: Nathan Bossart @ 2023-11-11 02:38 UTC (permalink / raw)
To: Andres Freund <[email protected]>; +Cc: pgsql-hackers
On Fri, Nov 10, 2023 at 03:11:50PM -0800, Andres Freund wrote:
> On 2023-11-10 14:51:28 -0600, Nathan Bossart wrote:
>> + * This read is guaranteed to read the current value,
>
> It doesn't guarantee that *at all*. What it guarantees is solely that the
> current CPU won't be doing something that could lead to reading an outdated
> value. To actually ensure the value is up2date, the modifying side also needs
> to have used a form of barrier (in the form of fetch_add, compare_exchange,
> etc or an explicit barrier).
Okay, I think I was missing that this doesn't work along with
pg_atomic_write_u32() because that doesn't have any barrier semantics
(probably because the spinlock version does). IIUC you'd want to use
pg_atomic_exchange_u32() to write the value instead, which seems to really
just be another compare/exchange under the hood.
Speaking of the spinlock implementation of pg_atomic_write_u32(), I've been
staring at this comment for a while and can't make sense of it:
void
pg_atomic_write_u32_impl(volatile pg_atomic_uint32 *ptr, uint32 val)
{
/*
* One might think that an unlocked write doesn't need to acquire the
* spinlock, but one would be wrong. Even an unlocked write has to cause a
* concurrent pg_atomic_compare_exchange_u32() (et al) to fail.
*/
SpinLockAcquire((slock_t *) &ptr->sema);
ptr->value = val;
SpinLockRelease((slock_t *) &ptr->sema);
}
It refers to "unlocked writes," but this isn't
pg_atomic_unlocked_write_u32_impl(). The original thread for this comment
[0] doesn't offer any hints, either. Does "unlocked" mean something
different here, such as "write without any barrier semantics?"
[0] https://postgr.es/m/14947.1475690465%40sss.pgh.pa.us
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com
^ permalink raw reply [nested|flat] 2+ messages in thread
end of thread, other threads:[~2023-11-11 02:38 UTC | newest]
Thread overview: 2+ messages (download: mbox mbox.gz follow: Atom feed)
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2021-03-03 05:24 [PATCH v2] windows: Only consider us to be running as service if stderr is invalid. Andres Freund <[email protected]>
2023-11-11 02:38 Re: locked reads for atomics Nathan Bossart <[email protected]>
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