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Date: Thu, 14 Feb 2019 14:29:53 +0100
From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: cygwin@cygwin.com
Subject: Re: Problem with cygserver (LookupAccountSid()) -- interlocking with its clients
Message-ID: <20190214132953.GE30859@calimero.vinschen.de>
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On Feb 13 20:35, Lavrentiev, Anton (NIH/NLM/NCBI) [C] via cygwin wrote:
> Hi all,
>=20
> We're having the following problem (on a subset(*) of Windows-10
> machines) with running cygserver.
>=20
> Started afresh, strace shows no activity in it, but should I execute a
> command (ipcs in the example below), then cygserver begins to
> experience freezes like these:
>=20
> 5295758 62716455 [unknown (0x2110)] cygserver 7248
> pwdgrp::fetch_account_from_windows:
> LookupAccountSid(S-1-5-5-0-89379457), Win32 error 1332

~5 secs, give or take.  I have no idea why this call should take
that long.  The problem here is that you can't know if that call
is really taking this long or any other action in between.
In fact, The result of LookupAccountSid here is fully expected.

> Look at the times, they are ginormous!  We also seem to have no idea
> what the shown SID is!  It looks very random, and changes when
> cygserver gets restarted.

S-1-5-5-0-89379457 is a logon SID, a unique per-user-session SID
part of the user token.  Nothing weird, nothing random.  This SID
usually only shows up inside the token so only a process calling
getgroups would see that.  In id(1) it shows up as gid 4095,
"CurrentSession".

When doing IPC stuff, cygserver impersonates the client and checks
all groups in the impersonation token.  It needs this info to
handle IPC permissions.

> (*)  All Windows-10 machines (~300) that we have here seem to have
> cygserver's pulling some random SIDs and failing with the same error,
> 1332.  But that usually happens pretty quickly (yet still,
> noticeable).  Only on a subset of hosts (less than 5%), we see these
> extremely long delays, causing the apps failures due to timeouts.

BLODA?


Corinna

--=20
Corinna Vinschen
Cygwin Maintainer

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