From: Dan Williams <dan.j.williams@intel.com>
To: Lv Zheng <lv.zheng@intel.com>
Cc: "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
"Rafael J . Wysocki" <rjw@rjwysocki.net>,
Len Brown <len.brown@intel.com>, Lv Zheng <zetalog@gmail.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux ACPI <linux-acpi@vger.kernel.org>
Subject: Re: [PATCH v5] ACPICA: Tables: Add mechanism to allow to balance late stage acpi_get_table() independently
Date: Tue, 6 Jun 2017 23:41:59 -0700 [thread overview]
Message-ID: <CAA9_cmdmokPM0+MSiMzGPzkvUkKPELrVyRPoO2bZZZoNJ2sr3w@mail.gmail.com> (raw)
In-Reply-To: <cb1126b2eb1b83a5a97a33c1c5c37a02c32fd688.1496811175.git.lv.zheng@intel.com>
On Tue, Jun 6, 2017 at 9:54 PM, Lv Zheng <lv.zheng@intel.com> wrote:
> Considering this case:
> 1. A program opens a sysfs table file 65535 times, it can increase
> validation_count and first increment cause the table to be mapped:
> validation_count = 65535
> 2. AML execution causes "Load" to be executed on the same table, this time
> it cannot increase validation_count, so validation_count remains:
> validation_count = 65535
> 3. The program closes sysfs table file 65535 times, it can decrease
> validation_count and the last decrement cause the table to be unmapped:
> validation_count = 0
> 4. AML code still accessing the loaded table, kernel crash can be observed.
>
> This is because orginally ACPICA doesn't support unmapping tables during
> OS late stage. So the current code only allows unmapping tables during OS
> early stage, and for late stage, no acpi_put_table() clones should be
> invoked, especially cases that can trigger frequent invocations of
> acpi_get_table()/acpi_put_table() are forbidden:
> 1. sysfs table accesses
> 2. dynamic Load/Unload opcode executions
> 3. acpi_load_table()
> 4. etc.
> Such frequent acpi_put_table() balance changes have to be done altogether.
>
> This philosophy is not convenient for Linux driver writers. Since the API
> is just there, developers will start to use acpi_put_table() during late
> stage. So we need to consider a better mechanism to allow them to safely
> invoke acpi_put_table().
>
> This patch provides such a mechanism by adding a validation_count
> threashold. When it is reached, the validation_count can no longer be
> incremented/decremented to invalidate the table descriptor (means
> preventing table unmappings) so that acpi_put_table() balance changes can be
> done independently to each others.
>
> Note: code added in acpi_tb_put_table() is actually a no-op but changes the
> warning message into a warning once message. Lv Zheng.
>
This still seems to be unnecessary gymnastics to keep the validation
count around and make it work for random drivers. Which ACPI tables
might be hot removed? If it's only a small handful of tables why not
teach the code that handles those exceptional cases to manage a
dedicated reference count mechanism? That way the other cases can be
left alone and not worry about balancing their references.
next prev parent reply other threads:[~2017-06-07 6:42 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
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 [this message]
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=CAA9_cmdmokPM0+MSiMzGPzkvUkKPELrVyRPoO2bZZZoNJ2sr3w@mail.gmail.com \
--to=dan.j.williams@intel.com \
--cc=len.brown@intel.com \
--cc=linux-acpi@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=lv.zheng@intel.com \
--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).