From 9910159f06590c17df4fbddedaabb4c0201cc4cb Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Mon, 15 Dec 2025 14:17:23 +0100 Subject: iio: core: add separate lockdep class for info_exist_lock When one iio device is a consumer of another, it is possible that the ->info_exist_lock of both ends up being taken when reading the value of the consumer device. Since they currently belong to the same lockdep class (being initialized in a single location with mutex_init()), that results in a lockdep warning CPU0 ---- lock(&iio_dev_opaque->info_exist_lock); lock(&iio_dev_opaque->info_exist_lock); *** DEADLOCK *** May be due to missing lock nesting notation 4 locks held by sensors/414: #0: c31fd6dc (&p->lock){+.+.}-{3:3}, at: seq_read_iter+0x44/0x4e4 #1: c4f5a1c4 (&of->mutex){+.+.}-{3:3}, at: kernfs_seq_start+0x1c/0xac #2: c2827548 (kn->active#34){.+.+}-{0:0}, at: kernfs_seq_start+0x30/0xac #3: c1dd2b68 (&iio_dev_opaque->info_exist_lock){+.+.}-{3:3}, at: iio_read_channel_processed_scale+0x24/0xd8 stack backtrace: CPU: 0 UID: 0 PID: 414 Comm: sensors Not tainted 6.17.11 #5 NONE Hardware name: Generic AM33XX (Flattened Device Tree) Call trace: unwind_backtrace from show_stack+0x10/0x14 show_stack from dump_stack_lvl+0x44/0x60 dump_stack_lvl from print_deadlock_bug+0x2b8/0x334 print_deadlock_bug from __lock_acquire+0x13a4/0x2ab0 __lock_acquire from lock_acquire+0xd0/0x2c0 lock_acquire from __mutex_lock+0xa0/0xe8c __mutex_lock from mutex_lock_nested+0x1c/0x24 mutex_lock_nested from iio_read_channel_raw+0x20/0x6c iio_read_channel_raw from rescale_read_raw+0x128/0x1c4 rescale_read_raw from iio_channel_read+0xe4/0xf4 iio_channel_read from iio_read_channel_processed_scale+0x6c/0xd8 iio_read_channel_processed_scale from iio_hwmon_read_val+0x68/0xbc iio_hwmon_read_val from dev_attr_show+0x18/0x48 dev_attr_show from sysfs_kf_seq_show+0x80/0x110 sysfs_kf_seq_show from seq_read_iter+0xdc/0x4e4 seq_read_iter from vfs_read+0x238/0x2e4 vfs_read from ksys_read+0x6c/0xec ksys_read from ret_fast_syscall+0x0/0x1c Just as the mlock_key already has its own lockdep class, add a lock_class_key for the info_exist mutex. Note that this has in theory been a problem since before IIO first left staging, but it only occurs when a chain of consumers is in use and that is not often done. Fixes: ac917a81117c ("staging:iio:core set the iio_dev.info pointer to null on unregister under lock.") Signed-off-by: Rasmus Villemoes Reviewed-by: Peter Rosin Cc: Signed-off-by: Jonathan Cameron --- include/linux/iio/iio-opaque.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/linux') diff --git a/include/linux/iio/iio-opaque.h b/include/linux/iio/iio-opaque.h index 4247497f3f8b..b87841a355f8 100644 --- a/include/linux/iio/iio-opaque.h +++ b/include/linux/iio/iio-opaque.h @@ -14,6 +14,7 @@ * @mlock: lock used to prevent simultaneous device state changes * @mlock_key: lockdep class for iio_dev lock * @info_exist_lock: lock to prevent use during removal + * @info_exist_key: lockdep class for info_exist lock * @trig_readonly: mark the current trigger immutable * @event_interface: event chrdevs associated with interrupt lines * @attached_buffers: array of buffers statically attached by the driver @@ -47,6 +48,7 @@ struct iio_dev_opaque { struct mutex mlock; struct lock_class_key mlock_key; struct mutex info_exist_lock; + struct lock_class_key info_exist_key; bool trig_readonly; struct iio_event_interface *event_interface; struct iio_buffer **attached_buffers; -- cgit v1.2.3