From: "Zheng, Lv" <lv.zheng@intel.com>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: "Wysocki, Rafael J" <rafael.j.wysocki@intel.com>,
"Brown, Len" <len.brown@intel.com>, Lv Zheng <zetalog@gmail.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
"Williams, Dan J" <dan.j.williams@intel.com>
Subject: RE: [PATCH v3 2/4] ACPICA: Tables: Add mechanism to allow to balance late stage acpi_get_table() independently
Date: Thu, 4 May 2017 07:18:28 +0000 [thread overview]
Message-ID: <1AE640813FDE7649BE1B193DEA596E886CE9D136@SHSMSX101.ccr.corp.intel.com> (raw)
In-Reply-To: <3915288.8qJPC28FTg@aspire.rjw.lan>
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 <dan.j.williams@intel.com>
> > Signed-off-by: Lv Zheng <lv.zheng@intel.com>
> > ---
> > 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.
When it is reached, validation_count will remain 65535 from then on (see both acpi_tb_get_table()/acpi_tb_put_table()).
When it is reached, the 65535 validation count ensures "the old behavior" - for late stage;
When it is not reached, the 65535 validation count ensures "the new behavior" - for early stage.
Then you can see, if there's no acpi_put_table() invoked for such old behavior dependent users, the validation count can also remain 65535.
That's why I said PATCH 3 is actually breaking things.
IMO, if we really want the acpi_put_table() balance work proceeded without waiting for the ACPICA upstream to change.
We need this commit.
I actually generated this commit once.
But hesitated to send it to ACPICA upstream as it didn't look like a good idea to increase communication cost to upstream a commit that hadn't been determined to be used by ACPICA.
However if other driver maintainers want to make their acpi_get_table() invocations balanced like what Dan did here.
This commit is required.
Thanks and best regards
Lv
>
> > return_VOID;
> > }
> > + if (table_desc->validation_count == 0) {
> > + ACPI_ERROR((AE_INFO,
> > + "Table %p, Validation count is zero before decrement\n",
> > + table_desc));
> > + return_VOID;
> > + }
> > table_desc->validation_count--;
> >
> > if (table_desc->validation_count == 0) {
> >
>
> Thanks,
> Rafael
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-acpi" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
next prev parent reply other threads:[~2017-05-04 7:18 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-27 8:22 [PATCH v2 1/2] ACPICA: Tables: Fix regression introduced by a too early mechanism enabling Lv Zheng
2017-04-27 8:22 ` [PATCH v2 2/2] ACPI: Fix memory mapping leaks in current sysfs dumpable ACPI tables support Lv Zheng
2017-04-27 22:32 ` Rafael J. Wysocki
2017-04-27 22:30 ` [PATCH v2 1/2] ACPICA: Tables: Fix regression introduced by a too early mechanism enabling Rafael J. Wysocki
2017-04-28 1:24 ` Zheng, Lv
2017-04-28 3:57 ` Zheng, Lv
2017-04-28 5:27 ` [PATCH v2 1/4] " Lv Zheng
2017-04-28 5:28 ` [PATCH v3 " Lv Zheng
2017-04-28 5:30 ` [PATCH v3 2/4] ACPICA: Tables: Add mechanism to allow to balance late stage acpi_get_table() independently Lv Zheng
2017-04-28 20:56 ` Rafael J. Wysocki
2017-05-04 7:18 ` Zheng, Lv [this message]
2017-05-04 15:45 ` Dan Williams
2017-05-05 0:53 ` Zheng, Lv
2017-05-05 20:43 ` Rafael J. Wysocki
2017-05-09 1:58 ` Zheng, Lv
2017-04-28 5:30 ` [PATCH v3 3/4] ACPI: sysfs: Fix acpi_get_table() leak Lv Zheng
2017-04-28 5:30 ` [PATCH v3 4/4] ACPI: Fix memory mapping leaks in current sysfs dumpable ACPI tables support Lv Zheng
2017-05-09 5:57 ` [PATCH v4 1/4] ACPICA: Tables: Fix regression introduced by a too early mechanism enabling Lv Zheng
2017-05-09 5:57 ` [PATCH v4 2/4] ACPICA: Tables: Add mechanism to allow to balance late stage acpi_get_table() independently Lv Zheng
2017-05-12 21:03 ` Rafael J. Wysocki
2017-05-12 21:41 ` Rafael J. Wysocki
2017-05-15 6:32 ` Zheng, Lv
2017-05-09 5:57 ` [PATCH v4 3/4] ACPI: sysfs: Fix acpi_get_table() leak Lv Zheng
2017-05-09 5:57 ` [PATCH v4 4/4] ACPI: Fix memory mapping leaks in current sysfs dumpable ACPI tables support Lv Zheng
2017-06-12 13:12 ` Rafael J. Wysocki
2017-06-07 4:54 ` [PATCH v5] ACPICA: Tables: Add mechanism to allow to balance late stage acpi_get_table() independently Lv Zheng
2017-06-07 6:41 ` Dan Williams
2017-06-07 21:14 ` Rafael J. Wysocki
2017-06-07 21:24 ` Dan Williams
2017-06-08 2:24 ` Zheng, Lv
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1AE640813FDE7649BE1B193DEA596E886CE9D136@SHSMSX101.ccr.corp.intel.com \
--to=lv.zheng@intel.com \
--cc=dan.j.williams@intel.com \
--cc=len.brown@intel.com \
--cc=linux-acpi@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=rafael.j.wysocki@intel.com \
--cc=rjw@rjwysocki.net \
--cc=zetalog@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).