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SubjectRe: ABBA deadlock in Common Clock Framework
On Wed, Jul 02, 2014 at 12:59:04PM +0200, Tomasz Figa wrote:
> Hi All,
>
> While testing linux-next (next-20140625) on Exynos4412-based TRATS2
> board, from time to time I hit a deadlock between clk_disable_unused()
> of Common Clock Framework and parallel clk_prepare() from s3c24xx-i2c
> driver.
>
> I believe the following is happening (in processes 1 and 2):
> 1: clk_disable_unused()
> 1: clk_prepare_lock()
> 1: mutex_lock(clk prepare mutex) // lock A
> 1: max77686_clk_is_prepared()
> 1: regmap_read()
> 2: regulator_set_voltage()
> 2: regmap_read()
> 2: mutex_lock(max77686 regmap mutex) // lock B
> 2: i2c_transfer()
> 2: s3c24xx_i2c_xfer()
> 2: clk_unprepare()
> 2: clk_prepare_lock()
> 2: mutex_lock(clk prepare mutex) // lock A
> 1: mutex_lock(max77686 regmap mutex) // lock B
> 1,2: BOOM!
>
> I suppose this is a general problem affecting any MFD device that is
> also a clock provider, but I clearly don't have a good idea what to do
> about it.
>

Or if you use notifiers which use i2c... See also
http://comments.gmane.org/gmane.linux.kernel/1553699. One workaround is to
always leave the clock of the i2c controller in a prepared state.

Cheers,

Peter.


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