From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Lv Zheng <lv.zheng@intel.com>,
"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: Wed, 7 Jun 2017 23:14:27 +0200 [thread overview]
Message-ID: <CAJZ5v0j6ZB=JXvDX3hjoRK-Eir3ZWVda2yvqkyT31X0EWLa03g@mail.gmail.com> (raw)
In-Reply-To: <CAA9_cmdmokPM0+MSiMzGPzkvUkKPELrVyRPoO2bZZZoNJ2sr3w@mail.gmail.com>
On Wed, Jun 7, 2017 at 8:41 AM, Dan Williams <dan.j.williams@intel.com> wrote:
> 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.
Well, I'm not sure I agree here.
If we can make it work at one point, it should not be too hard to
maintain that status.
Thanks,
Rafael
next prev parent reply other threads:[~2017-06-07 21:14 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
2017-06-07 21:14 ` Rafael J. Wysocki [this message]
2017-06-07 21:24 ` Dan Williams
2017-06-08 2:24 ` Zheng, Lv
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