From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754406AbdEIB6u convert rfc822-to-8bit (ORCPT ); Mon, 8 May 2017 21:58:50 -0400 Received: from mga06.intel.com ([134.134.136.31]:18535 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751958AbdEIB6q (ORCPT ); Mon, 8 May 2017 21:58:46 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.38,311,1491289200"; d="scan'208";a="99043283" From: "Zheng, Lv" To: "Rafael J. Wysocki" CC: "Wysocki, Rafael J" , "Brown, Len" , Lv Zheng , "linux-kernel@vger.kernel.org" , "linux-acpi@vger.kernel.org" , "Williams, Dan J" Subject: RE: [PATCH v3 2/4] ACPICA: Tables: Add mechanism to allow to balance late stage acpi_get_table() independently Thread-Topic: [PATCH v3 2/4] ACPICA: Tables: Add mechanism to allow to balance late stage acpi_get_table() independently Thread-Index: AQHSv+CY3mvNHNDihkmJngBm+ytV0qHavdAAgAkI1oCAAfPoAIAFlOEQ Date: Tue, 9 May 2017 01:58:40 +0000 Message-ID: <1AE640813FDE7649BE1B193DEA596E886CEA018F@SHSMSX101.ccr.corp.intel.com> References: <5361b51c7c257b3216475018a3a5cc4f8b6b21c6.1493281247.git.lv.zheng@intel.com> <3915288.8qJPC28FTg@aspire.rjw.lan> <1AE640813FDE7649BE1B193DEA596E886CE9D136@SHSMSX101.ccr.corp.intel.com> <2006722.863OfZUBRq@aspire.rjw.lan> In-Reply-To: <2006722.863OfZUBRq@aspire.rjw.lan> Accept-Language: zh-CN, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-titus-metadata-40: eyJDYXRlZ29yeUxhYmVscyI6IiIsIk1ldGFkYXRhIjp7Im5zIjoiaHR0cDpcL1wvd3d3LnRpdHVzLmNvbVwvbnNcL0ludGVsMyIsImlkIjoiNWNmZWM2OTEtNDYxYi00N2I1LWI5MzYtNTg1MTMwNzlkMDJiIiwicHJvcHMiOlt7Im4iOiJDVFBDbGFzc2lmaWNhdGlvbiIsInZhbHMiOlt7InZhbHVlIjoiQ1RQX0lDIn1dfV19LCJTdWJqZWN0TGFiZWxzIjpbXSwiVE1DVmVyc2lvbiI6IjE1LjkuNi42IiwiVHJ1c3RlZExhYmVsSGFzaCI6IlwvWXhWcFJcLzlubktWMU9zd3BhcXdKdFhJME1kdXdlbjFOcVo1bStSWk5RVT0ifQ== x-ctpclassification: CTP_IC dlp-product: dlpe-windows dlp-version: 10.0.102.7 dlp-reaction: no-action x-originating-ip: [10.239.127.40] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, > From: linux-acpi-owner@vger.kernel.org [mailto:linux-acpi-owner@vger.kernel.org] On Behalf Of Rafael J. > Wysocki > Subject: Re: [PATCH v3 2/4] ACPICA: Tables: Add mechanism to allow to balance late stage > acpi_get_table() independently > > On Thursday, May 04, 2017 07:18:28 AM Zheng, Lv wrote: > > Hi, Rafael > > > > > From: linux-acpi-owner@vger.kernel.org [mailto:linux-acpi-owner@vger.kernel.org] On Behalf Of > Rafael J. > > > Wysocki > > > Subject: Re: [PATCH v3 2/4] ACPICA: Tables: Add mechanism to allow to balance late stage > > > acpi_get_table() independently > > > > > > On Friday, April 28, 2017 01:30:20 PM Lv Zheng wrote: > > > > For all frequent late stage acpi_get_table() clone invocations, we should > > > > only fix them altogether, otherwise, excessive acpi_put_table() could > > > > unexpectedly unmap the table used by the other users. Thus the current plan > > > > is to fix all acpi_get_table() clones together or to fix none of them. > > > > > > I honestly don't think that fixing none of them is a valid option here. > > > > That's just exactly the old behavior, maybe shouldn't be called as "fix". > > Should say "change to use the new behavior together" all stay unchanged. > > > > I actually want to make the change from ACPICA side. > > But it's costly to persuade ACPICA upstream to take both the > "acpi_get_table_with_size()/early_acpi_os_unmap_memory() divergence reduction" change and the "table > map on-demand" change. > > > > So we just made 2 things separated, and did 1 thing once. > > > > > > > > > This prevents kernel developers from improving the late stage code quality > > > > without waiting for the ACPICA upstream to improve first. > > > > > > > > This patch adds a mechanism to stop decrementing validation count to > > > > prevent the table unmapping operations so that acpi_put_table() balance > > > > fixes can be done independently to each others. > > > > > > > > Cc: Dan Williams > > > > Signed-off-by: Lv Zheng > > > > --- > > > > drivers/acpi/acpica/tbutils.c | 10 ++++++++-- > > > > 1 file changed, 8 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/drivers/acpi/acpica/tbutils.c b/drivers/acpi/acpica/tbutils.c > > > > index 7abe665..b517bd0 100644 > > > > --- a/drivers/acpi/acpica/tbutils.c > > > > +++ b/drivers/acpi/acpica/tbutils.c > > > > @@ -445,12 +445,18 @@ void acpi_tb_put_table(struct acpi_table_desc *table_desc) > > > > > > > > ACPI_FUNCTION_TRACE(acpi_tb_put_table); > > > > > > > > - if (table_desc->validation_count == 0) { > > > > + if ((table_desc->validation_count + 1) == 0) { > > > > > > This means that validation_count has reached the maximum value, right? > > > > > > > ACPI_WARNING((AE_INFO, > > > > - "Table %p, Validation count is zero before decrement\n", > > > > + "Table %p, Validation count is about to expire, decrement is unsafe\n", > > > > table_desc)); > > > > > > So why is it unsafe to decrement it? > > > > Considering this case: > > A program opens a sysfs table file 65535 times: validation_count = 65535. > > Load opcode is invoked by the AML interpreter, but it cannot increase the validation count, see > acpi_tb_get_table(): validation_count = 65535. > > Now the program closes the sysfs table file: validation_count = 0, which triggers table unmap. > > But it is likely that the AML code is still accessing the namespace objects provided by this table. > > A kernel crash then can be seen. > > > > So after applying this patch, 65535 now is the threshold. > > OK, so this is overflow detection in disguise. :-) > > It is quite confusing, IMO. It would be better to define a limit symbol like > ACPI_TABLE_VCOUNT_MAX below the natural maximum of the data type > (say, make it equal to 65534 if the data type is unsigned short int) and then > make *both* acpi_tb_get_table() and acpi_tb_put_table() refuse to update > validation_count *and* print a "validation count overflow" message once it > has become greater than ACPI_TABLE_VCOUNT_MAX (in which case it will > natrually stay at ACPI_TABLE_VCOUNT_MAX+1). OK, I'll also make the error message less verbose in the next revision. Thanks, Lv