From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mga06.intel.com (mga06.intel.com [134.134.136.31])
 by mx.groups.io with SMTP id smtpd.web11.600.1577086711145639272
 for <devel@edk2.groups.io>;
 Sun, 22 Dec 2019 23:38:31 -0800
Authentication-Results: mx.groups.io;
 dkim=missing; spf=pass (domain: intel.com, ip: 134.134.136.31, mailfrom: ray.ni@intel.com)
X-Amp-Result: SKIPPED(no attachment in message)
X-Amp-File-Uploaded: False
Received: from orsmga007.jf.intel.com ([10.7.209.58])
  by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 22 Dec 2019 23:38:30 -0800
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="5.69,346,1571727600"; 
   d="scan'208";a="207184488"
Received: from fmsmsx108.amr.corp.intel.com ([10.18.124.206])
  by orsmga007.jf.intel.com with ESMTP; 22 Dec 2019 23:38:30 -0800
Received: from FMSMSX109.amr.corp.intel.com (10.18.116.9) by
 FMSMSX108.amr.corp.intel.com (10.18.124.206) with Microsoft SMTP Server (TLS)
 id 14.3.439.0; Sun, 22 Dec 2019 23:38:30 -0800
Received: from shsmsx106.ccr.corp.intel.com (10.239.4.159) by
 fmsmsx109.amr.corp.intel.com (10.18.116.9) with Microsoft SMTP Server (TLS)
 id 14.3.439.0; Sun, 22 Dec 2019 23:38:30 -0800
Received: from shsmsx104.ccr.corp.intel.com ([169.254.5.90]) by
 SHSMSX106.ccr.corp.intel.com ([169.254.10.236]) with mapi id 14.03.0439.000;
 Mon, 23 Dec 2019 15:38:28 +0800
From: "Ni, Ray" <ray.ni@intel.com>
To: "devel@edk2.groups.io" <devel@edk2.groups.io>, "Dong, Eric"
	<eric.dong@intel.com>
CC: Laszlo Ersek <lersek@redhat.com>
Subject: Re: [edk2-devel] [PATCH v2 1/2] UefiCpuPkg/PiSmmCpuDxeSmm: Remove dependence between APs
Thread-Topic: [edk2-devel] [PATCH v2 1/2] UefiCpuPkg/PiSmmCpuDxeSmm: Remove
 dependence between APs
Thread-Index: AQHVuVz0JLgSVfRhGkKbSI5iGEufJ6fHUE1g
Date: Mon, 23 Dec 2019 07:38:28 +0000
Message-ID: <734D49CCEBEEF84792F5B80ED585239D5C3A8DBD@SHSMSX104.ccr.corp.intel.com>
References: <20191223064806.682-1-eric.dong@intel.com>
 <20191223064806.682-2-eric.dong@intel.com>
In-Reply-To: <20191223064806.682-2-eric.dong@intel.com>
Accept-Language: en-US, zh-CN
X-MS-Has-Attach: 
X-MS-TNEF-Correlator: 
x-originating-ip: [10.239.127.40]
MIME-Version: 1.0
Return-Path: ray.ni@intel.com
Content-Language: en-US
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable

>=20
> +  WaitForSemaphore (&Token->RunningApCount);=20
> +=20
> +  if (Token->RunningApCount =3D=3D 0) {
> +    ReleaseSpinLock (Token->SpinLock);=20
>    }

1. if (InterlockedDecrement (&Token->RunningApCount) =3D=3D 0) {
      ReleaseSpinLock (Token->SpinLock);
    }

We should avoid checking RunningApCount directly because it's possible
that AP#1 decrease the Count to 1 and before AP#1 checks the value against =
0
the Count is decreased by AP#2 to 0. So that causes AP#1 and AP#2 call
ReleaseSpinLock() on the same SpinLock.

>=20
> +      // Decrease the count to mark this AP as finished.

2. BSP is also handled here. So this comment is mis-leading.

>=20
> +      //
>=20
> +      if (Token !=3D NULL) {=20
> +        WaitForSemaphore (&ProcToken->RunningApCount);

3. The code is written correctly but improperly IMO.
Token is checked but ProcToken is deferenced.
I suggest you check ProcToken directly.