Re: [PATCH v6 14/24] iio: buffer: wrap all buffer attributes into iio_dev_attr

[Alexandru Ardelean <ardeleanalex@gmail.com>]

On Thu, Apr 1, 2021 at 11:29 AM Jonathan Cameron
<Jonathan.Cameron@huawei.com> wrote:
>
> On Thu, 1 Apr 2021 09:39:47 +0200
> Marek Szyprowski <m.szyprowski@samsung.com> wrote:
>
> > Hi
> >
> > On 15.02.2021 11:40, Alexandru Ardelean wrote:
> > > This change wraps all buffer attributes into iio_dev_attr objects, and
> > > assigns a reference to the IIO buffer they belong to.
> > >
> > > With the addition of multiple IIO buffers per one IIO device, we need a way
> > > to know which IIO buffer is being enabled/disabled/controlled.
> > >
> > > We know that all buffer attributes are device_attributes. So we can wrap
> > > them with a iio_dev_attr types. In the iio_dev_attr type, we can also hold
> > > a reference to an IIO buffer.
> > > So, we end up being able to allocate wrapped attributes for all buffer
> > > attributes (even the one from other drivers).
> > >
> > > The neat part with this mechanism, is that we don't need to add any extra
> > > cleanup, because these attributes are being added to a dynamic list that
> > > will get cleaned up via iio_free_chan_devattr_list().
> > >
> > > With this change, the 'buffer->scan_el_dev_attr_list' list is being renamed
> > > to 'buffer->buffer_attr_list', effectively merging (or finalizing the
> > > merge) of the buffer/ & scan_elements/ attributes internally.
> > >
> > > Accessing these new buffer attributes can now be done via
> > > 'to_iio_dev_attr(attr)->buffer' inside the show/store handlers.
> > >
> > > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> >
> > This patch landed recently in linux-next as commit 15097c7a1adc ("iio:
> > buffer: wrap all buffer attributes into iio_dev_attr"). Sadly it causes
> > a regression and triggers the lock debuging warning:
> >
> > ak8975 9-000c: mounting matrix not found: using identity...
> > ak8975 9-000c: supply vdd not found, using dummy regulator
> > ak8975 9-000c: supply vid not found, using dummy regulator
> > BUG: key cf40d08c has not been registered!
> > ------------[ cut here ]------------
> > WARNING: CPU: 2 PID: 1 at kernel/locking/lockdep.c:4686
> > __kernfs_create_file+0x7c/0xfc
> > DEBUG_LOCKS_WARN_ON(1)
> > Modules linked in:
> > CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.12.0-rc2-00153-g15097c7a1adc
> > #2828
> > Hardware name: Samsung Exynos (Flattened Device Tree)
> > [<c011170c>] (unwind_backtrace) from [<c010cf74>] (show_stack+0x10/0x14)
> > [<c010cf74>] (show_stack) from [<c0b48650>] (dump_stack+0xa4/0xc4)
> > [<c0b48650>] (dump_stack) from [<c01274c8>] (__warn+0x118/0x11c)
> > [<c01274c8>] (__warn) from [<c0127544>] (warn_slowpath_fmt+0x78/0xbc)
> > [<c0127544>] (warn_slowpath_fmt) from [<c038db90>]
> > (__kernfs_create_file+0x7c/0xfc)
> > [<c038db90>] (__kernfs_create_file) from [<c038e870>]
> > (sysfs_add_file_mode_ns+0xa0/0x1cc)
> > [<c038e870>] (sysfs_add_file_mode_ns) from [<c038f4e0>]
> > (internal_create_group+0x138/0x3f4)
> > [<c038f4e0>] (internal_create_group) from [<c038fd64>]
> > (internal_create_groups+0x48/0x88)
> > [<c038fd64>] (internal_create_groups) from [<c06a8754>]
> > (device_add+0x2e4/0x7ec)
> > [<c06a8754>] (device_add) from [<c02e46a0>] (cdev_device_add+0x48/0x80)
> > [<c02e46a0>] (cdev_device_add) from [<c08db1a4>]
> > (__iio_device_register+0x670/0x7c0)
> > [<c08db1a4>] (__iio_device_register) from [<c08e2efc>]
> > (ak8975_probe+0x3a4/0x584)
> > [<c08e2efc>] (ak8975_probe) from [<c082e120>] (i2c_device_probe+0x234/0x2a4)
> > [<c082e120>] (i2c_device_probe) from [<c06abea4>] (really_probe+0x1d4/0x4ec)
> > [<c06abea4>] (really_probe) from [<c06ac234>]
> > (driver_probe_device+0x78/0x1d8)
> > [<c06ac234>] (driver_probe_device) from [<c06ac74c>]
> > (device_driver_attach+0x58/0x60)
> > [<c06ac74c>] (device_driver_attach) from [<c06ac850>]
> > (__driver_attach+0xfc/0x160)
> > [<c06ac850>] (__driver_attach) from [<c06a9e58>]
> > (bus_for_each_dev+0x6c/0xb8)
> > [<c06a9e58>] (bus_for_each_dev) from [<c06aaf90>]
> > (bus_add_driver+0x170/0x20c)
> > [<c06aaf90>] (bus_add_driver) from [<c06ad6c8>] (driver_register+0x78/0x10c)
> > [<c06ad6c8>] (driver_register) from [<c082f0d4>]
> > (i2c_register_driver+0x3c/0xac)
> > [<c082f0d4>] (i2c_register_driver) from [<c0102434>]
> > (do_one_initcall+0x88/0x430)
> > [<c0102434>] (do_one_initcall) from [<c11010d4>]
> > (kernel_init_freeable+0x190/0x1e0)
> > [<c11010d4>] (kernel_init_freeable) from [<c0b4c564>]
> > (kernel_init+0x8/0x118)
> > [<c0b4c564>] (kernel_init) from [<c010011c>] (ret_from_fork+0x14/0x38)
> > Exception stack(0xc1d09fb0 to 0xc1d09ff8)
> > 9fa0:                                     00000000 00000000 00000000
> > 00000000
> > 9fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> > 00000000
> > 9fe0: 00000000 00000000 00000000 00000000 00000013 00000000
> > irq event stamp: 485619
> > hardirqs last  enabled at (485619): [<c01a51fc>] console_unlock+0x500/0x648
> > hardirqs last disabled at (485618): [<c01a51e0>] console_unlock+0x4e4/0x648
> > softirqs last  enabled at (484774): [<c0101790>] __do_softirq+0x528/0x63c
> > softirqs last disabled at (484769): [<c0130a38>] irq_exit+0x1f4/0x1fc
> > ---[ end trace 21850020cbfb3350 ]---
> >
> > The above warning is probably caused by copying struct device_attribute
> > objects in iio_buffer_wrap_attr() without re-initializing
> > spinlocks/mutexes. Locks debuging depends on the spinlock/mutex
> > initializers, which register them (as absolute value of the pointer to
> > them) to the debugging engine. After copying the structures, the objects
> > don't match the pointers they were registered. I didn't have time to
> > analyze it further and find which object/lock is triggering this though.
>
> Thanks, interestingly there aren't any spinlocks or mutexes in attributes,
> but there are lock_class_keys. Looks like we need to call sysfs_attr_init()
> and I guess we are currently missing it on this path.
>
> Alex, can you take a look?  If not I'll get to it sometime over the weekend
> most likely.

Will take a look.

>
> Jonathan
>
>
> >
> > > ---
> > >   drivers/iio/industrialio-buffer.c | 76 ++++++++++++++++++++-----------
> > >   include/linux/iio/buffer_impl.h   |  4 +-
> > >   2 files changed, 52 insertions(+), 28 deletions(-)
> > >
> > > diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> > > index e6edec3bcb73..8dc140f13b99 100644
> > > --- a/drivers/iio/industrialio-buffer.c
> > > +++ b/drivers/iio/industrialio-buffer.c
> > > @@ -253,8 +253,7 @@ static ssize_t iio_scan_el_show(struct device *dev,
> > >                             char *buf)
> > >   {
> > >     int ret;
> > > -   struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -   struct iio_buffer *buffer = indio_dev->buffer;
> > > +   struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >
> > >     /* Ensure ret is 0 or 1. */
> > >     ret = !!test_bit(to_iio_dev_attr(attr)->address,
> > > @@ -367,8 +366,8 @@ static ssize_t iio_scan_el_store(struct device *dev,
> > >     int ret;
> > >     bool state;
> > >     struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -   struct iio_buffer *buffer = indio_dev->buffer;
> > >     struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
> > > +   struct iio_buffer *buffer = this_attr->buffer;
> > >
> > >     ret = strtobool(buf, &state);
> > >     if (ret < 0)
> > > @@ -402,8 +401,7 @@ static ssize_t iio_scan_el_ts_show(struct device *dev,
> > >                                struct device_attribute *attr,
> > >                                char *buf)
> > >   {
> > > -   struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -   struct iio_buffer *buffer = indio_dev->buffer;
> > > +   struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >
> > >     return sprintf(buf, "%d\n", buffer->scan_timestamp);
> > >   }
> > > @@ -415,7 +413,7 @@ static ssize_t iio_scan_el_ts_store(struct device *dev,
> > >   {
> > >     int ret;
> > >     struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -   struct iio_buffer *buffer = indio_dev->buffer;
> > > +   struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >     bool state;
> > >
> > >     ret = strtobool(buf, &state);
> > > @@ -448,7 +446,7 @@ static int iio_buffer_add_channel_sysfs(struct iio_dev *indio_dev,
> > >                                  IIO_SEPARATE,
> > >                                  &indio_dev->dev,
> > >                                  buffer,
> > > -                                &buffer->scan_el_dev_attr_list);
> > > +                                &buffer->buffer_attr_list);
> > >     if (ret)
> > >             return ret;
> > >     attrcount++;
> > > @@ -460,7 +458,7 @@ static int iio_buffer_add_channel_sysfs(struct iio_dev *indio_dev,
> > >                                  0,
> > >                                  &indio_dev->dev,
> > >                                  buffer,
> > > -                                &buffer->scan_el_dev_attr_list);
> > > +                                &buffer->buffer_attr_list);
> > >     if (ret)
> > >             return ret;
> > >     attrcount++;
> > > @@ -473,7 +471,7 @@ static int iio_buffer_add_channel_sysfs(struct iio_dev *indio_dev,
> > >                                          0,
> > >                                          &indio_dev->dev,
> > >                                          buffer,
> > > -                                        &buffer->scan_el_dev_attr_list);
> > > +                                        &buffer->buffer_attr_list);
> > >     else
> > >             ret = __iio_add_chan_devattr("en",
> > >                                          chan,
> > > @@ -483,7 +481,7 @@ static int iio_buffer_add_channel_sysfs(struct iio_dev *indio_dev,
> > >                                          0,
> > >                                          &indio_dev->dev,
> > >                                          buffer,
> > > -                                        &buffer->scan_el_dev_attr_list);
> > > +                                        &buffer->buffer_attr_list);
> > >     if (ret)
> > >             return ret;
> > >     attrcount++;
> > > @@ -495,8 +493,7 @@ static ssize_t iio_buffer_read_length(struct device *dev,
> > >                                   struct device_attribute *attr,
> > >                                   char *buf)
> > >   {
> > > -   struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -   struct iio_buffer *buffer = indio_dev->buffer;
> > > +   struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >
> > >     return sprintf(buf, "%d\n", buffer->length);
> > >   }
> > > @@ -506,7 +503,7 @@ static ssize_t iio_buffer_write_length(struct device *dev,
> > >                                    const char *buf, size_t len)
> > >   {
> > >     struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -   struct iio_buffer *buffer = indio_dev->buffer;
> > > +   struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >     unsigned int val;
> > >     int ret;
> > >
> > > @@ -538,8 +535,7 @@ static ssize_t iio_buffer_show_enable(struct device *dev,
> > >                                   struct device_attribute *attr,
> > >                                   char *buf)
> > >   {
> > > -   struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -   struct iio_buffer *buffer = indio_dev->buffer;
> > > +   struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >
> > >     return sprintf(buf, "%d\n", iio_buffer_is_active(buffer));
> > >   }
> > > @@ -1154,7 +1150,7 @@ static ssize_t iio_buffer_store_enable(struct device *dev,
> > >     int ret;
> > >     bool requested_state;
> > >     struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -   struct iio_buffer *buffer = indio_dev->buffer;
> > > +   struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >     bool inlist;
> > >
> > >     ret = strtobool(buf, &requested_state);
> > > @@ -1183,8 +1179,7 @@ static ssize_t iio_buffer_show_watermark(struct device *dev,
> > >                                      struct device_attribute *attr,
> > >                                      char *buf)
> > >   {
> > > -   struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -   struct iio_buffer *buffer = indio_dev->buffer;
> > > +   struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >
> > >     return sprintf(buf, "%u\n", buffer->watermark);
> > >   }
> > > @@ -1195,7 +1190,7 @@ static ssize_t iio_buffer_store_watermark(struct device *dev,
> > >                                       size_t len)
> > >   {
> > >     struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -   struct iio_buffer *buffer = indio_dev->buffer;
> > > +   struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >     unsigned int val;
> > >     int ret;
> > >
> > > @@ -1228,8 +1223,7 @@ static ssize_t iio_dma_show_data_available(struct device *dev,
> > >                                             struct device_attribute *attr,
> > >                                             char *buf)
> > >   {
> > > -   struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -   struct iio_buffer *buffer = indio_dev->buffer;
> > > +   struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >
> > >     return sprintf(buf, "%zu\n", iio_buffer_data_available(buffer));
> > >   }
> > > @@ -1254,6 +1248,26 @@ static struct attribute *iio_buffer_attrs[] = {
> > >     &dev_attr_data_available.attr,
> > >   };
> > >
> > > +#define to_dev_attr(_attr) container_of(_attr, struct device_attribute, attr)
> > > +
> > > +static struct attribute *iio_buffer_wrap_attr(struct iio_buffer *buffer,
> > > +                                         struct attribute *attr)
> > > +{
> > > +   struct device_attribute *dattr = to_dev_attr(attr);
> > > +   struct iio_dev_attr *iio_attr;
> > > +
> > > +   iio_attr = kzalloc(sizeof(*iio_attr), GFP_KERNEL);
> > > +   if (!iio_attr)
> > > +           return NULL;
> > > +
> > > +   iio_attr->buffer = buffer;
> > > +   memcpy(&iio_attr->dev_attr, dattr, sizeof(iio_attr->dev_attr));
> > > +
> > > +   list_add(&iio_attr->l, &buffer->buffer_attr_list);
> > > +
> > > +   return &iio_attr->dev_attr.attr;
> > > +}
> > > +
> > >   static int iio_buffer_register_legacy_sysfs_groups(struct iio_dev *indio_dev,
> > >                                                struct attribute **buffer_attrs,
> > >                                                int buffer_attrcount,
> > > @@ -1329,7 +1343,7 @@ static int __iio_buffer_alloc_sysfs_and_mask(struct iio_buffer *buffer,
> > >     }
> > >
> > >     scan_el_attrcount = 0;
> > > -   INIT_LIST_HEAD(&buffer->scan_el_dev_attr_list);
> > > +   INIT_LIST_HEAD(&buffer->buffer_attr_list);
> > >     channels = indio_dev->channels;
> > >     if (channels) {
> > >             /* new magic */
> > > @@ -1376,9 +1390,19 @@ static int __iio_buffer_alloc_sysfs_and_mask(struct iio_buffer *buffer,
> > >
> > >     buffer_attrcount += ARRAY_SIZE(iio_buffer_attrs);
> > >
> > > -   attrn = buffer_attrcount;
> > > +   for (i = 0; i < buffer_attrcount; i++) {
> > > +           struct attribute *wrapped;
> > > +
> > > +           wrapped = iio_buffer_wrap_attr(buffer, attr[i]);
> > > +           if (!wrapped) {
> > > +                   ret = -ENOMEM;
> > > +                   goto error_free_scan_mask;
> > > +           }
> > > +           attr[i] = wrapped;
> > > +   }
> > >
> > > -   list_for_each_entry(p, &buffer->scan_el_dev_attr_list, l)
> > > +   attrn = 0;
> > > +   list_for_each_entry(p, &buffer->buffer_attr_list, l)
> > >             attr[attrn++] = &p->dev_attr.attr;
> > >
> > >     buffer->buffer_group.name = kasprintf(GFP_KERNEL, "buffer%d", index);
> > > @@ -1412,7 +1436,7 @@ static int __iio_buffer_alloc_sysfs_and_mask(struct iio_buffer *buffer,
> > >   error_free_scan_mask:
> > >     bitmap_free(buffer->scan_mask);
> > >   error_cleanup_dynamic:
> > > -   iio_free_chan_devattr_list(&buffer->scan_el_dev_attr_list);
> > > +   iio_free_chan_devattr_list(&buffer->buffer_attr_list);
> > >
> > >     return ret;
> > >   }
> > > @@ -1443,7 +1467,7 @@ static void __iio_buffer_free_sysfs_and_mask(struct iio_buffer *buffer)
> > >     bitmap_free(buffer->scan_mask);
> > >     kfree(buffer->buffer_group.name);
> > >     kfree(buffer->buffer_group.attrs);
> > > -   iio_free_chan_devattr_list(&buffer->scan_el_dev_attr_list);
> > > +   iio_free_chan_devattr_list(&buffer->buffer_attr_list);
> > >   }
> > >
> > >   void iio_buffer_free_sysfs_and_mask(struct iio_dev *indio_dev)
> > > diff --git a/include/linux/iio/buffer_impl.h b/include/linux/iio/buffer_impl.h
> > > index 3e555e58475b..41044320e581 100644
> > > --- a/include/linux/iio/buffer_impl.h
> > > +++ b/include/linux/iio/buffer_impl.h
> > > @@ -97,8 +97,8 @@ struct iio_buffer {
> > >     /* @scan_timestamp: Does the scan mode include a timestamp. */
> > >     bool scan_timestamp;
> > >
> > > -   /* @scan_el_dev_attr_list: List of scan element related attributes. */
> > > -   struct list_head scan_el_dev_attr_list;
> > > +   /* @buffer_attr_list: List of buffer attributes. */
> > > +   struct list_head buffer_attr_list;
> > >
> > >     /*
> > >      * @buffer_group: Attributes of the new buffer group.
> >
> > Best regards
>