Re: [PATCH 09/14] mmc: jz4740: Fix race condition in IRQ mask update

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On 9 March 2018 at 19:49, James Hogan <jhogan@xxxxxxxxxx> wrote:
> On Fri, Mar 09, 2018 at 12:12:14PM -0300, Ezequiel Garcia wrote:
>> From: Alex Smith <alex.smith@xxxxxxxxxx>
>>
>> A spinlock is held while updating the internal copy of the IRQ mask,
>> but not while writing it to the actual IMASK register. After the lock
>> is released, an IRQ can occur before the IMASK register is written.
>> If handling this IRQ causes the mask to be changed, when the handler
>> returns back to the middle of the first mask update, a stale value
>> will be written to the mask register.
>>
>> If this causes an IRQ to become unmasked that cannot have its status
>> cleared by writing a 1 to it in the IREG register, e.g. the SDIO IRQ,
>> then we can end up stuck with the same IRQ repeatedly being fired but
>> not handled. Normally the MMC IRQ handler attempts to clear any
>> unexpected IRQs by writing IREG, but for those that cannot be cleared
>> in this way then the IRQ will just repeatedly fire.
>>
>> This was resulting in lockups after a while of using Wi-Fi on the
>> CI20 (GitHub issue #19).
>>
>> Resolve by holding the spinlock until after the IMASK register has
>> been updated.
>>
>
> Maybe have a Link tag instead of referencing "github issue #19", i.e.:
> Link: https://github.com/MIPS/CI20_linux/issues/19
>
> Since this fixes an older commit, it'd be worth adding:
>
> Fixes: 61bfbdb85687 ("MMC: Add support for the controller on JZ4740 SoCs.")
>
>> Signed-off-by: Alex Smith <alex.smith@xxxxxxxxxx>
>
> ... and presumably is worthy of backporting (the driver was introduced
> in 2.6.36), i.e.:
> Cc: stable@xxxxxxxxxxxxxxx
>

Oh, yes, good catch. I've overlooked this commit.

Thanks,
-- 
Ezequiel García, VanguardiaSur
www.vanguardiasur.com.ar
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