On Fri, May 14, 2021 at 11:36 PM Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
>
> Removing an iio-driver module (or unbinding the driver) causes a BUG() to
> trigger when the kernel is build with list-debugging enabled. This is
> caused by a double list_del() introduced by commit 8dedcc3eee3a ("iio:
> core: centralize ioctl() calls to the main chardev").
>
> This patch introduces an ioctl_handlers list to which ioctl handlers are
> added. The cleanup of these however happens twice.
>
> The 2 registration functions:
> iio_device_ioctl_handler_register()
> iio_device_register_eventset()
>
> Have matching unregister functions which do a list_del on the head added
> to the list; and iio_device_unregister() has:
>
> list_for_each_entry_safe(h, t, &iio_dev_opaque->ioctl_handlers, entry)
> list_del(&h->entry);
This patch should already be in the fixes-togreg tree of IIO.
I am not sure when/if it went in next.
https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git/commit/?h=fixes-togreg&id=901f84de0e16bde10a72d7eb2f2eb73fcde8fa1a
>
> This is a problem because iio_device_unregister() does this before calling
> iio_buffers_free_sysfs_and_mask() which calls
> iio_device_ioctl_handler_unregister() which calls list_del on the entry
> added by iio_buffers_alloc_sysfs_and_mask() a second time causing this:
>
> [root@fedora ~]# rmmod bmc150_accel_i2c
> Segmentation fault
>
> [ 160.627546] ------------[ cut here ]------------
> [ 160.627549] kernel BUG at lib/list_debug.c:45!
> [ 160.629125] invalid opcode: 0000 [#1] SMP PTI
> [ 160.629140] CPU: 0 PID: 1139 Comm: rmmod Tainted: G E 5.13.0-rc1+ #341
> [ 160.629146] Hardware name: LENOVO 80M1/Mini, BIOS C7CN31WW 08/05/2016
> [ 160.629149] RIP: 0010:__list_del_entry_valid.cold+0xf/0x47
> ...
> [ 160.629202] Call Trace:
> [ 160.629209] iio_device_ioctl_handler_unregister+0xe/0x90 [industrialio]
> [ 160.629226] iio_device_unregister_trigger_consumer+0x21d/0x2f0 [industrialio]
> [ 160.629239] bmc150_accel_core_remove+0x20/0xd0 [bmc150_accel_core]
> [ 160.629246] i2c_device_remove+0x25/0xb0
> [ 160.629254] __device_release_driver+0x180/0x240
> [ 160.629261] device_release_driver+0x26/0x40
> [ 160.629267] bus_remove_device+0xf2/0x160
> [ 160.629272] device_del+0x18c/0x3e0
> [ 160.629280] device_unregister+0x16/0x60
> ...
>
> Since iio_device_ioctl_handler_unregister/iio_device_unregister_eventset()
> already do the list_del() there is no need for the
> list_for_each_entry_safe() in iio_device_unregister() which also does the
> list_del(). Remove the list_for_each_entry_safe() to fix the double
> list_del() issue.
>
> Fixes: 8dedcc3eee3a ("iio: core: centralize ioctl() calls to the main chardev")
> Cc: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
> Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
> ---
> drivers/iio/industrialio-core.c | 6 ------
> 1 file changed, 6 deletions(-)
>
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index d92c58a94fe4..9e59f5da3d28 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -1926,9 +1926,6 @@ EXPORT_SYMBOL(__iio_device_register);
> **/
> void iio_device_unregister(struct iio_dev *indio_dev)
> {
> - struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
> - struct iio_ioctl_handler *h, *t;
> -
> cdev_device_del(&indio_dev->chrdev, &indio_dev->dev);
>
> mutex_lock(&indio_dev->info_exist_lock);
> @@ -1939,9 +1936,6 @@ void iio_device_unregister(struct iio_dev *indio_dev)
>
> indio_dev->info = NULL;
>
> - list_for_each_entry_safe(h, t, &iio_dev_opaque->ioctl_handlers, entry)
> - list_del(&h->entry);
> -
> iio_device_wakeup_eventset(indio_dev);
> iio_buffer_wakeup_poll(indio_dev);
>
> --
> 2.31.1
>
