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Message-ID: <20211017181311.57928c49@jic23-huawei>
Date: Sun, 17 Oct 2021 18:13:11 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org,
Pengutronix Kernel Team <kernel@...gutronix.de>,
David Jander <david@...tonic.nl>,
Robin van der Gracht <robin@...tonic.nl>,
linux-iio@...r.kernel.org, Lars-Peter Clausen <lars@...afoo.de>,
Peter Meerwald-Stadler <pmeerw@...erw.net>,
Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: Re: [PATCH v2 2/2] iio: adc: tsc2046: fix sleeping in atomic
context warning and a deadlock after iio_trigger_poll() call
On Thu, 7 Oct 2021 11:30:07 +0200
Oleksij Rempel <o.rempel@...gutronix.de> wrote:
> If iio_trigger_poll() is called after IRQ was disabled, we will call
> reenable_trigger() directly from hard IRQ or hrtimer context instead of
> IRQ thread. In this case we will run in to multiple issue as sleeping in atomic
> context and a deadlock.
>
> To avoid this issue, rework the trigger to use state machine. All state
> changes are done over the hrtimer, so it allows us to drop fsleep() and
> avoid the deadlock.
>
> Even if the root cause of this issue probably will and can be fixed in the iio
> core, this patch can be seen as clean-up to provide better internal state
> machine.
>
> Fixes: 9374e8f5a38d ("iio: adc: add ADC driver for the TI TSC2046 controller")
> Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
So, I promised a core fix and haven't sent one yet.
I'm not that keen on this complexity in the driver as to my mind it should need
a complex state machine to deal with this.
Let me knock up a quick patch and then be lazy and ask you to test it for me.
The main delay on that I'd have have figure out a test framework for it rather
than the actual change.
So far I haven't found a clean race free route to ensure in general that we don't
get a lack of balance between trigger occuring + reenable vs enable / disable.
So we may still need some state in the individual drivers but it should be simple.
In this particular case the reference counting on disable_irq may be enough but
I'm not quite sure so you may want to look closely at that.
Jonathan
> ---
> drivers/iio/adc/ti-tsc2046.c | 102 ++++++++++++++++++++---------------
> 1 file changed, 58 insertions(+), 44 deletions(-)
>
> diff --git a/drivers/iio/adc/ti-tsc2046.c b/drivers/iio/adc/ti-tsc2046.c
> index d84ae6b008c1..91f6bd5effe7 100644
> --- a/drivers/iio/adc/ti-tsc2046.c
> +++ b/drivers/iio/adc/ti-tsc2046.c
> @@ -123,14 +123,21 @@ struct tsc2046_adc_ch_cfg {
> unsigned int oversampling_ratio;
> };
>
> +enum tsc2046_state {
> + TSC2046_STATE_STANDBY,
> + TSC2046_STATE_ENABLE_IRQ_POLL,
> + TSC2046_STATE_POLL,
> + TSC2046_STATE_ENABLE_IRQ,
> +};
> +
> struct tsc2046_adc_priv {
> struct spi_device *spi;
> const struct tsc2046_adc_dcfg *dcfg;
>
> struct iio_trigger *trig;
> struct hrtimer trig_timer;
> - spinlock_t trig_lock;
> - unsigned int trig_more_count;
> + enum tsc2046_state state;
> + spinlock_t state_lock;
>
> struct spi_transfer xfer;
> struct spi_message msg;
> @@ -411,21 +418,47 @@ static const struct iio_info tsc2046_adc_info = {
> .update_scan_mode = tsc2046_adc_update_scan_mode,
> };
>
> -static enum hrtimer_restart tsc2046_adc_trig_more(struct hrtimer *hrtimer)
> +static enum hrtimer_restart tsc2046_adc_timer(struct hrtimer *hrtimer)
> {
> struct tsc2046_adc_priv *priv = container_of(hrtimer,
> struct tsc2046_adc_priv,
> trig_timer);
> unsigned long flags;
>
> - spin_lock_irqsave(&priv->trig_lock, flags);
> -
> - disable_irq_nosync(priv->spi->irq);
> -
> - priv->trig_more_count++;
> - iio_trigger_poll(priv->trig);
> -
> - spin_unlock_irqrestore(&priv->trig_lock, flags);
> + spin_lock_irqsave(&priv->state_lock, flags);
> + switch (priv->state) {
> + case TSC2046_STATE_ENABLE_IRQ_POLL:
> + /*
> + * IRQ handler called iio_trigger_poll() to sample ADC.
> + * Here we
> + * - re-enable IRQs
> + * - start hrtimer for timeout if no IRQ will occur
> + */
> + priv->state = TSC2046_STATE_POLL;
> + enable_irq(priv->spi->irq);
> + hrtimer_start(&priv->trig_timer,
> + ns_to_ktime(priv->scan_interval_us *
> + NSEC_PER_USEC),
> + HRTIMER_MODE_REL_SOFT);
> + break;
> + case TSC2046_STATE_POLL:
> + disable_irq_nosync(priv->spi->irq);
> + priv->state = TSC2046_STATE_ENABLE_IRQ;
> + /* iio_trigger_poll() starts hrtimer */
> + iio_trigger_poll(priv->trig);
> + break;
> + case TSC2046_STATE_ENABLE_IRQ:
> + priv->state = TSC2046_STATE_STANDBY;
> + enable_irq(priv->spi->irq);
> + break;
> + case TSC2046_STATE_STANDBY:
> + fallthrough;
> + default:
> + dev_warn(&priv->spi->dev, "Got unexpected state: %i\n",
> + priv->state);
> + break;
> + }
> + spin_unlock_irqrestore(&priv->state_lock, flags);
>
> return HRTIMER_NORESTART;
> }
> @@ -434,16 +467,17 @@ static irqreturn_t tsc2046_adc_irq(int irq, void *dev_id)
> {
> struct iio_dev *indio_dev = dev_id;
> struct tsc2046_adc_priv *priv = iio_priv(indio_dev);
> -
> - spin_lock(&priv->trig_lock);
> + unsigned long flags;
>
> hrtimer_try_to_cancel(&priv->trig_timer);
>
> - priv->trig_more_count = 0;
> + spin_lock_irqsave(&priv->state_lock, flags);
> disable_irq_nosync(priv->spi->irq);
> - iio_trigger_poll(priv->trig);
> + priv->state = TSC2046_STATE_ENABLE_IRQ_POLL;
>
> - spin_unlock(&priv->trig_lock);
> + /* iio_trigger_poll() starts hrtimer */
> + iio_trigger_poll(priv->trig);
> + spin_unlock_irqrestore(&priv->state_lock, flags);
>
> return IRQ_HANDLED;
> }
> @@ -452,37 +486,16 @@ static void tsc2046_adc_reenable_trigger(struct iio_trigger *trig)
> {
> struct iio_dev *indio_dev = iio_trigger_get_drvdata(trig);
> struct tsc2046_adc_priv *priv = iio_priv(indio_dev);
> - unsigned long flags;
> - int delta;
> + ktime_t tim;
>
> /*
> * We can sample it as fast as we can, but usually we do not need so
> * many samples. Reduce the sample rate for default (touchscreen) use
> * case.
> - * Currently we do not need a highly precise sample rate. It is enough
> - * to have calculated numbers.
> - */
> - delta = priv->scan_interval_us - priv->time_per_scan_us;
> - if (delta > 0)
> - fsleep(delta);
> -
> - spin_lock_irqsave(&priv->trig_lock, flags);
> -
> - /*
> - * We need to trigger at least one extra sample to detect state
> - * difference on ADC side.
> */
> - if (!priv->trig_more_count) {
> - int timeout_ms = DIV_ROUND_UP(priv->scan_interval_us,
> - USEC_PER_MSEC);
> -
> - hrtimer_start(&priv->trig_timer, ms_to_ktime(timeout_ms),
> - HRTIMER_MODE_REL_SOFT);
> - }
> -
> - enable_irq(priv->spi->irq);
> -
> - spin_unlock_irqrestore(&priv->trig_lock, flags);
> + tim = ns_to_ktime((priv->scan_interval_us - priv->time_per_scan_us) *
> + NSEC_PER_USEC);
> + hrtimer_start(&priv->trig_timer, tim, HRTIMER_MODE_REL_SOFT);
> }
>
> static int tsc2046_adc_set_trigger_state(struct iio_trigger *trig, bool enable)
> @@ -493,8 +506,8 @@ static int tsc2046_adc_set_trigger_state(struct iio_trigger *trig, bool enable)
> if (enable) {
> enable_irq(priv->spi->irq);
> } else {
> + hrtimer_cancel(&priv->trig_timer);
> disable_irq(priv->spi->irq);
> - hrtimer_try_to_cancel(&priv->trig_timer);
> }
>
> return 0;
> @@ -668,10 +681,11 @@ static int tsc2046_adc_probe(struct spi_device *spi)
> iio_trigger_set_drvdata(trig, indio_dev);
> trig->ops = &tsc2046_adc_trigger_ops;
>
> - spin_lock_init(&priv->trig_lock);
> + spin_lock_init(&priv->state_lock);
> + priv->state = TSC2046_STATE_STANDBY;
> hrtimer_init(&priv->trig_timer, CLOCK_MONOTONIC,
> HRTIMER_MODE_REL_SOFT);
> - priv->trig_timer.function = tsc2046_adc_trig_more;
> + priv->trig_timer.function = tsc2046_adc_timer;
>
> ret = devm_iio_trigger_register(dev, trig);
> if (ret) {
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