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SubjectRe: [PATCH v3 1/3] counter: 104-quad-8: Add lock guards - generic interface
On Thu, Mar 12, 2020 at 04:54:38PM +0530, Syed Nayyar Waris wrote:
> Add lock protection from race conditions to 104-quad-8 counter
> driver generic interface code changes. There is no IRQ handling so spin_lock calls
> are used for protection.
>
> Fixes: f1d8a071d45b ("counter: 104-quad-8: Add Generic Counter interface
> support")
>
> Signed-off-by: Syed Nayyar Waris <syednwaris@gmail.com>
>
> Split the patch from filter clock prescaler and differential encoder
> cable status changes. Also, include more code statements for protection
> using spin_lock calls and remove protection from few code statements as
> they were unnecessary.
> ---

Hello Syed,

Text above the "---" line will be saved as part of the commit message,
which is not what we want for review comments. Move your comments to
below this line instead; this patch I submitted recently is a good
example of the format:
https://lore.kernel.org/linux-iio/20200301220719.25173-1-vilhelm.gray@gmail.com/

I have some more changes for this patch, but we're almost finished. :-)

> drivers/counter/104-quad-8.c | 174 ++++++++++++++++++++++++++++++++++++-------
> 1 file changed, 149 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
> index 9dab190..7d42303 100644
> --- a/drivers/counter/104-quad-8.c
> +++ b/drivers/counter/104-quad-8.c
> @@ -44,6 +44,7 @@ MODULE_PARM_DESC(base, "ACCES 104-QUAD-8 base addresses");
> * @base: base port address of the IIO device
> */
> struct quad8_iio {
> + spinlock_t lock;
> struct counter_device counter;
> unsigned int fck_prescaler[QUAD8_NUM_COUNTERS];
> unsigned int preset[QUAD8_NUM_COUNTERS];
> @@ -123,6 +124,8 @@ static int quad8_read_raw(struct iio_dev *indio_dev,
> /* Borrow XOR Carry effectively doubles count range */
> *val = (borrow ^ carry) << 24;
>
> + spin_lock(&priv->lock);
> +
> /* Reset Byte Pointer; transfer Counter to Output Latch */
> outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_BP | QUAD8_RLD_CNTR_OUT,
> base_offset + 1);
> @@ -130,6 +133,8 @@ static int quad8_read_raw(struct iio_dev *indio_dev,
> for (i = 0; i < 3; i++)
> *val |= (unsigned int)inb(base_offset) << (8 * i);
>
> + spin_unlock(&priv->lock);
> +
> return IIO_VAL_INT;
> case IIO_CHAN_INFO_ENABLE:
> *val = priv->ab_enable[chan->channel];
> @@ -160,6 +165,8 @@ static int quad8_write_raw(struct iio_dev *indio_dev,
> if ((unsigned int)val > 0xFFFFFF)
> return -EINVAL;
>
> + spin_lock(&priv->lock);
> +
> /* Reset Byte Pointer */
> outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_BP, base_offset + 1);
>
> @@ -183,12 +190,16 @@ static int quad8_write_raw(struct iio_dev *indio_dev,
> /* Reset Error flag */
> outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_E, base_offset + 1);
>
> + spin_unlock(&priv->lock);
> +
> return 0;
> case IIO_CHAN_INFO_ENABLE:
> /* only boolean values accepted */
> if (val < 0 || val > 1)
> return -EINVAL;
>
> + spin_lock(&priv->lock);
> +
> priv->ab_enable[chan->channel] = val;
>
> ior_cfg = val | priv->preset_enable[chan->channel] << 1;
> @@ -196,8 +207,12 @@ static int quad8_write_raw(struct iio_dev *indio_dev,
> /* Load I/O control configuration */
> outb(QUAD8_CTR_IOR | ior_cfg, base_offset + 1);
>
> + spin_unlock(&priv->lock);
> +
> return 0;
> case IIO_CHAN_INFO_SCALE:
> + spin_lock(&priv->lock);
> +
> /* Quadrature scaling only available in quadrature mode */
> if (!priv->quadrature_mode[chan->channel] && (val2 || val != 1))
> return -EINVAL;

We will need to careful here because there are some return statements;
we are bound to deadlock if we return without calling spin_unlock first.

There are a couple ways I can think of that allow you to resolve this:
for example you can call spin_unlock before every return statement, or
maybe create a goto that calls spin_unlock and then returns -EINVAL;
I'll leave it up for you to decide how to solve this.

> @@ -219,6 +234,8 @@ static int quad8_write_raw(struct iio_dev *indio_dev,
> else
> return -EINVAL;
>
> + spin_unlock(&priv->lock);
> +
> return 0;
> }
>
> @@ -255,6 +272,8 @@ static ssize_t quad8_write_preset(struct iio_dev *indio_dev, uintptr_t private,
> if (preset > 0xFFFFFF)
> return -EINVAL;
>
> + spin_lock(&priv->lock);
> +
> priv->preset[chan->channel] = preset;
>
> /* Reset Byte Pointer */
> @@ -264,6 +283,8 @@ static ssize_t quad8_write_preset(struct iio_dev *indio_dev, uintptr_t private,
> for (i = 0; i < 3; i++)
> outb(preset >> (8 * i), base_offset);
>
> + spin_unlock(&priv->lock);
> +
> return len;
> }
>
> @@ -293,6 +314,8 @@ static ssize_t quad8_write_set_to_preset_on_index(struct iio_dev *indio_dev,
> /* Preset enable is active low in Input/Output Control register */
> preset_enable = !preset_enable;
>
> + spin_lock(&priv->lock);
> +
> priv->preset_enable[chan->channel] = preset_enable;
>
> ior_cfg = priv->ab_enable[chan->channel] |
> @@ -301,6 +324,8 @@ static ssize_t quad8_write_set_to_preset_on_index(struct iio_dev *indio_dev,
> /* Load I/O control configuration to Input / Output Control Register */
> outb(QUAD8_CTR_IOR | ior_cfg, base_offset);
>
> + spin_unlock(&priv->lock);
> +
> return len;
> }
>
> @@ -358,6 +383,8 @@ static int quad8_set_count_mode(struct iio_dev *indio_dev,
> unsigned int mode_cfg = cnt_mode << 1;
> const int base_offset = priv->base + 2 * chan->channel + 1;
>
> + spin_lock(&priv->lock);
> +
> priv->count_mode[chan->channel] = cnt_mode;
>
> /* Add quadrature mode configuration */
> @@ -367,6 +394,8 @@ static int quad8_set_count_mode(struct iio_dev *indio_dev,
> /* Load mode configuration to Counter Mode Register */
> outb(QUAD8_CTR_CMR | mode_cfg, base_offset);
>
> + spin_unlock(&priv->lock);
> +
> return 0;
> }
>
> @@ -394,9 +423,13 @@ static int quad8_set_synchronous_mode(struct iio_dev *indio_dev,
> const struct iio_chan_spec *chan, unsigned int synchronous_mode)
> {
> struct quad8_iio *const priv = iio_priv(indio_dev);
> - const unsigned int idr_cfg = synchronous_mode |
> - priv->index_polarity[chan->channel] << 1;
> const int base_offset = priv->base + 2 * chan->channel + 1;
> + unsigned int idr_cfg;

The synchronous_mode parameter does not need protection so you can
initialize idr_cfg to it immediately:

unsigned int idr_cfg = synchronous_mode;

> +
> + spin_lock(&priv->lock);
> +
> + idr_cfg = synchronous_mode |
> + priv->index_polarity[chan->channel] << 1;

Since we set idr_cfg to synchronous_mode earlier, this line can become:

idr_cfg |= priv->index_polarity[chan->channel] << 1;

>
> /* Index function must be non-synchronous in non-quadrature mode */
> if (synchronous_mode && !priv->quadrature_mode[chan->channel])

There is a return statement here that could create a deadlock situation.
To resolve this, you can call spin_unlock before the return statement.

> @@ -407,6 +440,8 @@ static int quad8_set_synchronous_mode(struct iio_dev *indio_dev,
> /* Load Index Control configuration to Index Control Register */
> outb(QUAD8_CTR_IDR | idr_cfg, base_offset);
>
> + spin_unlock(&priv->lock);
> +
> return 0;
> }
>
> @@ -434,8 +469,12 @@ static int quad8_set_quadrature_mode(struct iio_dev *indio_dev,
> const struct iio_chan_spec *chan, unsigned int quadrature_mode)
> {
> struct quad8_iio *const priv = iio_priv(indio_dev);
> - unsigned int mode_cfg = priv->count_mode[chan->channel] << 1;
> const int base_offset = priv->base + 2 * chan->channel + 1;
> + unsigned int mode_cfg;
> +
> + spin_lock(&priv->lock);
> +
> + mode_cfg = priv->count_mode[chan->channel] << 1;
>
> if (quadrature_mode)
> mode_cfg |= (priv->quadrature_scale[chan->channel] + 1) << 3;
> @@ -453,6 +492,8 @@ static int quad8_set_quadrature_mode(struct iio_dev *indio_dev,
> /* Load mode configuration to Counter Mode Register */
> outb(QUAD8_CTR_CMR | mode_cfg, base_offset);
>
> + spin_unlock(&priv->lock);
> +
> return 0;
> }
>
> @@ -480,15 +521,21 @@ static int quad8_set_index_polarity(struct iio_dev *indio_dev,
> const struct iio_chan_spec *chan, unsigned int index_polarity)
> {
> struct quad8_iio *const priv = iio_priv(indio_dev);
> - const unsigned int idr_cfg = priv->synchronous_mode[chan->channel] |
> - index_polarity << 1;
> const int base_offset = priv->base + 2 * chan->channel + 1;
> + unsigned int idr_cfg;

The index_polarity parameter does not need protection so we can
initialize idr_cfg to it immediately:

unsigned int idr_cfg = index_polarity << 1;

> +
> + spin_lock(&priv->lock);
> +
> + idr_cfg = priv->synchronous_mode[chan->channel] |
> + index_polarity << 1;

Since we idr_cfg was set with index_polarity earlier, this line can
become:

idr_cfg |= priv->synchronous_mode[chan->channel];

>
> priv->index_polarity[chan->channel] = index_polarity;
>
> /* Load Index Control configuration to Index Control Register */
> outb(QUAD8_CTR_IDR | idr_cfg, base_offset);
>
> + spin_unlock(&priv->lock);
> +
> return 0;
> }
>
> @@ -603,6 +650,8 @@ static int quad8_count_read(struct counter_device *counter,
> /* Borrow XOR Carry effectively doubles count range */
> *val = (unsigned long)(borrow ^ carry) << 24;
>
> + spin_lock(&((struct quad8_iio *)priv)->lock);

You can redeclare priv throughout your patch to drop the const qualifier
whenever needed so that you don't need to constantly cast these
spin_lock/spin_unlock calls everywhere:

struct quad8_iio *const priv = counter->priv;
...
spin_lock(&priv->lock);
...
spin_unlock(&priv->lock);

> +
> /* Reset Byte Pointer; transfer Counter to Output Latch */
> outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_BP | QUAD8_RLD_CNTR_OUT,
> base_offset + 1);
> @@ -610,6 +659,8 @@ static int quad8_count_read(struct counter_device *counter,
> for (i = 0; i < 3; i++)
> *val |= (unsigned long)inb(base_offset) << (8 * i);
>
> + spin_unlock(&((struct quad8_iio *)priv)->lock);
> +
> return 0;
> }
>
> @@ -624,6 +675,8 @@ static int quad8_count_write(struct counter_device *counter,
> if (val > 0xFFFFFF)
> return -EINVAL;
>
> + spin_lock(&((struct quad8_iio *)priv)->lock);
> +
> /* Reset Byte Pointer */
> outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_BP, base_offset + 1);
>
> @@ -647,6 +700,8 @@ static int quad8_count_write(struct counter_device *counter,
> /* Reset Error flag */
> outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_E, base_offset + 1);
>
> + spin_unlock(&((struct quad8_iio *)priv)->lock);
> +
> return 0;
> }
>
> @@ -669,11 +724,11 @@ static int quad8_function_get(struct counter_device *counter,
> {
> const struct quad8_iio *const priv = counter->priv;
> const int id = count->id;
> - const unsigned int quadrature_mode = priv->quadrature_mode[id];
> - const unsigned int scale = priv->quadrature_scale[id];
>
> - if (quadrature_mode)
> - switch (scale) {
> + spin_lock(&((struct quad8_iio *)priv)->lock);
> +
> + if (priv->quadrature_mode[id])
> + switch (priv->quadrature_scale[id]) {
> case 0:
> *function = QUAD8_COUNT_FUNCTION_QUADRATURE_X1;
> break;
> @@ -687,6 +742,8 @@ static int quad8_function_get(struct counter_device *counter,
> else
> *function = QUAD8_COUNT_FUNCTION_PULSE_DIRECTION;
>
> + spin_unlock(&((struct quad8_iio *)priv)->lock);
> +
> return 0;
> }
>
> @@ -697,10 +754,15 @@ static int quad8_function_set(struct counter_device *counter,
> const int id = count->id;
> unsigned int *const quadrature_mode = priv->quadrature_mode + id;
> unsigned int *const scale = priv->quadrature_scale + id;
> - unsigned int mode_cfg = priv->count_mode[id] << 1;
> unsigned int *const synchronous_mode = priv->synchronous_mode + id;
> - const unsigned int idr_cfg = priv->index_polarity[id] << 1;
> const int base_offset = priv->base + 2 * id + 1;
> + unsigned int mode_cfg;
> + unsigned int idr_cfg;
> +
> + spin_lock(&priv->lock);
> +
> + mode_cfg = priv->count_mode[id] << 1;
> + idr_cfg = priv->index_polarity[id] << 1;
>
> if (function == QUAD8_COUNT_FUNCTION_PULSE_DIRECTION) {
> *quadrature_mode = 0;
> @@ -736,6 +798,8 @@ static int quad8_function_set(struct counter_device *counter,
> /* Load mode configuration to Counter Mode Register */
> outb(QUAD8_CTR_CMR | mode_cfg, base_offset);
>
> + spin_unlock(&priv->lock);
> +
> return 0;
> }
>
> @@ -852,15 +916,21 @@ static int quad8_index_polarity_set(struct counter_device *counter,
> {
> struct quad8_iio *const priv = counter->priv;
> const size_t channel_id = signal->id - 16;
> - const unsigned int idr_cfg = priv->synchronous_mode[channel_id] |
> - index_polarity << 1;
> const int base_offset = priv->base + 2 * channel_id + 1;
> + unsigned int idr_cfg;

The index_polarity parameter does not need to be protected so you can
initalized idr_cfg with it immediatedly:

unsigned int idr_cfg = index_polarity << 1;

> +
> + spin_lock(&priv->lock);
> +
> + idr_cfg = priv->synchronous_mode[channel_id] |
> + index_polarity << 1;

Since idr_cfg was already initialized with index_polarity, this line can
become:

idr_cfg |= priv->synchronous_mode[channel_id];

>
> priv->index_polarity[channel_id] = index_polarity;
>
> /* Load Index Control configuration to Index Control Register */
> outb(QUAD8_CTR_IDR | idr_cfg, base_offset);
>
> + spin_unlock(&priv->lock);
> +
> return 0;
> }
>
> @@ -887,9 +957,13 @@ static int quad8_synchronous_mode_set(struct counter_device *counter,
> {
> struct quad8_iio *const priv = counter->priv;
> const size_t channel_id = signal->id - 16;
> - const unsigned int idr_cfg = synchronous_mode |
> - priv->index_polarity[channel_id] << 1;
> const int base_offset = priv->base + 2 * channel_id + 1;
> + unsigned int idr_cfg;

The synchronous_mode parameter does not need to be protected so you can
initalized idr_cfg with it immediatedly:

unsigned int idr_cfg = synchronous_mode;

> +
> + spin_lock(&priv->lock);
> +
> + idr_cfg = synchronous_mode |
> + priv->index_polarity[channel_id] << 1;

Since idr_cfg was already initialized with synchronous_mode, this line
can become:

idr_cfg |= priv->index_polarity[channel_id] << 1;

>
> /* Index function must be non-synchronous in non-quadrature mode */
> if (synchronous_mode && !priv->quadrature_mode[channel_id])

There's a return statement here that can cause a deadlock. You should
call spin_unlock before the return statement.

> @@ -900,6 +974,8 @@ static int quad8_synchronous_mode_set(struct counter_device *counter,
> /* Load Index Control configuration to Index Control Register */
> outb(QUAD8_CTR_IDR | idr_cfg, base_offset);
>
> + spin_unlock(&priv->lock);
> +
> return 0;
> }
>
> @@ -964,6 +1040,8 @@ static int quad8_count_mode_set(struct counter_device *counter,
> break;
> }
>
> + spin_lock(&priv->lock);
> +
> priv->count_mode[count->id] = cnt_mode;
>
> /* Set count mode configuration value */
> @@ -976,6 +1054,8 @@ static int quad8_count_mode_set(struct counter_device *counter,
> /* Load mode configuration to Counter Mode Register */
> outb(QUAD8_CTR_CMR | mode_cfg, base_offset);
>
> + spin_unlock(&priv->lock);
> +
> return 0;
> }
>
> @@ -1017,6 +1097,8 @@ static ssize_t quad8_count_enable_write(struct counter_device *counter,
> if (err)
> return err;
>
> + spin_lock(&priv->lock);
> +
> priv->ab_enable[count->id] = ab_enable;
>
> ior_cfg = ab_enable | priv->preset_enable[count->id] << 1;
> @@ -1024,6 +1106,8 @@ static ssize_t quad8_count_enable_write(struct counter_device *counter,
> /* Load I/O control configuration */
> outb(QUAD8_CTR_IOR | ior_cfg, base_offset + 1);
>
> + spin_unlock(&priv->lock);
> +
> return len;
> }
>
> @@ -1052,6 +1136,22 @@ static ssize_t quad8_count_preset_read(struct counter_device *counter,
> return sprintf(buf, "%u\n", priv->preset[count->id]);
> }
>
> +void quad8_preset_register_set(struct counter_device *counter,
> + const int base_offset, int id, unsigned int preset)

We can simplify this parameter list some more because base_offset can be
determined by the id. I think something like the following would work:

void quad8_preset_register_set(struct quad8_iio *quad8iio,
unsigned int id, unsigned int preset)
{
const unsigned int base_offset = quad8iio->base + 2 * id;
...

> +{
> + struct quad8_iio *const priv = counter->priv;
> + int i;
> +
> + priv->preset[id] = preset;
> +
> + /* Reset Byte Pointer */
> + outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_BP, base_offset + 1);
> +
> + /* Set Preset Register */
> + for (i = 0; i < 3; i++)
> + outb(preset >> (8 * i), base_offset);
> +}
> +
> static ssize_t quad8_count_preset_write(struct counter_device *counter,
> struct counter_count *count, void *private, const char *buf, size_t len)
> {
> @@ -1059,7 +1159,6 @@ static ssize_t quad8_count_preset_write(struct counter_device *counter,
> const int base_offset = priv->base + 2 * count->id;

Defining base_offset here will no longer be necessary because the new
quad8_preset_register_set will define it, so you can delete this line.

> unsigned int preset;
> int ret;
> - int i;
>
> ret = kstrtouint(buf, 0, &preset);
> if (ret)
> @@ -1069,14 +1168,11 @@ static ssize_t quad8_count_preset_write(struct counter_device *counter,
> if (preset > 0xFFFFFF)
> return -EINVAL;
>
> - priv->preset[count->id] = preset;
> + spin_lock(&priv->lock);
>
> - /* Reset Byte Pointer */
> - outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_BP, base_offset + 1);
> + quad8_preset_register_set(counter, base_offset, count->id, preset);

This then becomes:

quad8_preset_register_set(priv, count->id, preset);

>
> - /* Set Preset Register */
> - for (i = 0; i < 3; i++)
> - outb(preset >> (8 * i), base_offset);
> + spin_unlock(&priv->lock);
>
> return len;
> }
> @@ -1086,13 +1182,17 @@ static ssize_t quad8_count_ceiling_read(struct counter_device *counter,
> {
> const struct quad8_iio *const priv = counter->priv;
>
> + spin_lock(&((struct quad8_iio *)priv)->lock);
> +
> /* Range Limit and Modulo-N count modes use preset value as ceiling */
> switch (priv->count_mode[count->id]) {
> case 1:
> case 3:
> - return quad8_count_preset_read(counter, count, private, buf);
> + return sprintf(buf, "%u\n", priv->preset[count->id]);
> }
>
> + spin_unlock(&((struct quad8_iio *)priv)->lock);
> +
> /* By default 0x1FFFFFF (25 bits unsigned) is maximum count */
> return sprintf(buf, "33554431\n");
> }
> @@ -1101,15 +1201,32 @@ static ssize_t quad8_count_ceiling_write(struct counter_device *counter,
> struct counter_count *count, void *private, const char *buf, size_t len)
> {
> struct quad8_iio *const priv = counter->priv;
> + const int base_offset = priv->base + 2 * count->id;

This base_offset can go away since it will be defined anyway in the
quad8_preset_register_set function.

> + unsigned int preset;

Rename this variable to "ceiling". Although ceiling and preset share the
same register, they are functionally different so it's best for us to
differentiate between the two.

> + int ret;
> +
> + spin_lock(&priv->lock);
>
> /* Range Limit and Modulo-N count modes use preset value as ceiling */
> switch (priv->count_mode[count->id]) {
> case 1:
> case 3:
> - return quad8_count_preset_write(counter, count, private, buf,
> - len);
> + ret = kstrtouint(buf, 0, &preset);
> + if (ret)
> + return ret;
> +
> + /* Only 24-bit values are supported */
> + if (preset > 0xFFFFFF)
> + return -EINVAL;

The kstrtouint call and 24-bit value check should occur outside of this
switch statement since this check is needed regardless of the count
mode. So something like this:

ret = kstrtouint(buf, 0, &ceiling);
if (ret)
return ret;

if (ceiling > 0xFFFFFF)
return -EINVAL;

spin_lock(&priv->lock);

switch (priv->count_mode[count->id]) {
...

> +
> + quad8_preset_register_set(counter, base_offset,
> + count->id, preset);

This becomes:

quad8_preset_register_set(priv, count->id, ceiling);

> +
> + return len;

This return is not needed. You can break here instead.

Sincerely,
William Breathitt Gray

> }
>
> + spin_unlock(&priv->lock);
> +
> return len;
> }
>
> @@ -1137,6 +1254,8 @@ static ssize_t quad8_count_preset_enable_write(struct counter_device *counter,
> /* Preset enable is active low in Input/Output Control register */
> preset_enable = !preset_enable;
>
> + spin_lock(&priv->lock);
> +
> priv->preset_enable[count->id] = preset_enable;
>
> ior_cfg = priv->ab_enable[count->id] | (unsigned int)preset_enable << 1;
> @@ -1144,6 +1263,8 @@ static ssize_t quad8_count_preset_enable_write(struct counter_device *counter,
> /* Load I/O control configuration to Input / Output Control Register */
> outb(QUAD8_CTR_IOR | ior_cfg, base_offset);
>
> + spin_unlock(&priv->lock);
> +
> return len;
> }
>
> @@ -1429,6 +1550,9 @@ static int quad8_probe(struct device *dev, unsigned int id)
> quad8iio->counter.priv = quad8iio;
> quad8iio->base = base[id];
>
> + /* Initialize spin lock */
> + spin_lock_init(&quad8iio->lock);
> +
> /* Reset all counters and disable interrupt function */
> outb(QUAD8_CHAN_OP_RESET_COUNTERS, base[id] + QUAD8_REG_CHAN_OP);
> /* Set initial configuration for all counters */
> --
> 2.7.4
>
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