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From: Shuah Khan <skhan@linuxfoundation.org>
To: Kees Cook <keescook@chromium.org>, gregkh@linuxfoundation.org
Cc: johannes@sipsolutions.net, rafael@kernel.org,
	linux-kernel@vger.kernel.org,
	Shuah Khan <skhan@linuxfoundation.org>
Subject: Re: [PATCH v2 04/11] drivers/base/devcoredump: convert devcd_count to counter_atomic32
Date: Wed, 7 Oct 2020 13:33:43 -0600	[thread overview]
Message-ID: <cb86761a-5531-cbb2-3987-0897771949b8@linuxfoundation.org> (raw)
In-Reply-To: <202010071114.EE9A2A47C@keescook>

On 10/7/20 12:15 PM, Kees Cook wrote:
> On Tue, Oct 06, 2020 at 02:44:35PM -0600, Shuah Khan wrote:
>> counter_atomic* is introduced to be used when a variable is used as
>> a simple counter and doesn't guard object lifetimes. This clearly
>> differentiates atomic_t usages that guard object lifetimes.
>>
>> counter_atomic* variables will wrap around to 0 when it overflows and
>> should not be used to guard resource lifetimes, device usage and
>> open counts that control state changes, and pm states.
>>
>> devcd_count is used to track dev_coredumpm device count and used in
>> device name string. It doesn't guard object lifetimes, device usage
>> counts, device open counts, and pm states. There is very little chance
>> of this counter overflowing. Convert it to use counter_atomic32.
>>
>> This conversion doesn't change the overflow wrap around behavior.
>>
>> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
> 
> I actually wonder if this should use refcount_t just because it is
> designed to be an alway-unique value. It is hard to imagine ever causing
> this to overflow, but why not let it be protected?
> 

This is one of the cases where devcd_count doesn't guard lifetimes,
however if it ever overflows, refcount_t is a better choice.

If we decide refcount_t is a better choice, I can drop this patch
and send refcount_t conversion patch instead.

Greg! Any thoughts on refcount_t for this being a better choice?


thanks,
-- Shuah

  reply	other threads:[~2020-10-07 19:33 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-06 20:44 [PATCH v2 00/11] Introduce Simple atomic counters Shuah Khan
2020-10-06 20:44 ` [PATCH v2 01/11] counters: Introduce counter_atomic* counters Shuah Khan
2020-10-07  9:04   ` Greg KH
2020-10-08 17:18     ` Shuah Khan
2020-10-07 18:11   ` Kees Cook
2020-10-07 19:26     ` Shuah Khan
2020-10-07 20:30       ` Kees Cook
2020-10-06 20:44 ` [PATCH v2 02/11] selftests:lib:test_counters: add new test for counters Shuah Khan
2020-10-07 18:12   ` Kees Cook
2020-10-06 20:44 ` [PATCH v2 03/11] drivers/base: convert deferred_trigger_count and probe_count to counter_atomic32 Shuah Khan
2020-10-07 18:13   ` Kees Cook
2020-10-06 20:44 ` [PATCH v2 04/11] drivers/base/devcoredump: convert devcd_count " Shuah Khan
2020-10-07 18:15   ` Kees Cook
2020-10-07 19:33     ` Shuah Khan [this message]
2020-10-07 19:38       ` Johannes Berg
2020-10-07 19:59         ` Shuah Khan
2020-10-07 20:43         ` Kees Cook
2020-10-08  6:42           ` Johannes Berg
2020-10-08  7:37             ` Kees Cook
2020-10-06 20:44 ` [PATCH v2 05/11] drivers/acpi: convert seqno counter_atomic32 Shuah Khan
2020-10-07 18:16   ` Kees Cook
2020-10-06 20:44 ` [PATCH v2 06/11] drivers/acpi/apei: " Shuah Khan
2020-10-07 18:17   ` Kees Cook
2020-10-06 20:44 ` [PATCH v2 07/11] drivers/android/binder: convert stats, transaction_log to counter_atomic32 Shuah Khan
2020-10-07 18:18   ` Kees Cook
2020-10-09 12:39   ` Christian Brauner
2020-10-06 20:44 ` [PATCH v2 08/11] drivers/base/test/test_async_driver_probe: convert to use counter_atomic32 Shuah Khan
2020-10-07 18:20   ` Kees Cook
2020-10-06 20:44 ` [PATCH v2 09/11] drivers/char/ipmi: convert stats " Shuah Khan
2020-10-07 18:21   ` Kees Cook
2020-10-06 20:44 ` [PATCH v2 10/11] drivers/misc/vmw_vmci: convert num guest devices counter to counter_atomic32 Shuah Khan
2020-10-07 18:27   ` Kees Cook
2020-10-08 17:12     ` Shuah Khan
2020-10-06 20:44 ` [PATCH v2 11/11] drivers/edac: convert pci counters " Shuah Khan
2020-10-07 18:28   ` Kees Cook
2020-10-07 18:30 ` [PATCH v2 00/11] Introduce Simple atomic counters Kees Cook

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