linux-kernel - Re: [PATCH 2/2] misc: sram: enable clock before registering regions

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Date:   Tue, 3 Jul 2018 15:30:09 +0300
From:   Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
To:     Johan Hovold <johan@...nel.org>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] misc: sram: enable clock before registering regions

On 07/03/2018 02:47 PM, Johan Hovold wrote:
> On Tue, Jul 03, 2018 at 01:23:30PM +0300, Vladimir Zapolskiy wrote:
>> Hi Johan,
>>
>> On 07/03/2018 01:05 PM, Johan Hovold wrote:
>>> Make sure to enable the clock before registering regions and exporting
>>> partitions to user space at which point we must be prepared for I/O.
>>>
>>> Fixes: ee895ccdf776 ("misc: sram: fix enabled clock leak on error path")
>>> Cc: Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
>>> Signed-off-by: Johan Hovold <johan@...nel.org>
>>
>> thank you for the change, however please note that the identified commit
>> for the fix is incorrect one apparently.
>>
>> In my opinion the proper tag contents would be
>>
>> Fixes: b4c3fcb3c71f ("misc: sram: extend usage of reserved partitions")
>>
>> I hope you agree to it, also I would suggest to swap the changes in
>> the series.
> 
> No, I think I used the right commit in the Fixes tag as that was the
> commit which moved the clock enable to after the memory-region
> registration (at which point the memory could potentially be accessed).

I was confused by the moved sram_reserve_regions() call, which was added
way later.

Allright, if it is assumed that gen_pool_get() interface requires only
a registered memory pool provider device, and it does, then there is
another kind of a problem, a SRAM/genpool consumer may not get access
to a valid region in SRAM before the latter is added to the SRAM pool
in sram_probe().

Instantly I don't know how to solve the issue above, it may require
a change to lib/genalloc.c to request a registration of genpool device
driver, but then such a change solves the problem identified by you
as well.

For your change as a proper (partial?) fix:

Reviewed-by: Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>

--
Best wishes,
Vladimir