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

[James Hogan <jhogan@kernel.org>]

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On Fri, Mar 09, 2018 at 12:12:14PM -0300, Ezequiel Garcia wrote:
> From: Alex Smith <alex.smith@imgtec.com>
> 
> 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@imgtec.com>

... and presumably is worthy of backporting (the driver was introduced
in 2.6.36), i.e.:
Cc: stable@vger.kernel.org

Cheers
James

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