FAILED: patch "[PATCH] iio: core: add separate lockdep class for info_exist_lock" failed to apply to 6.12-stable tree

FAILED: patch "[PATCH] iio: core: add separate lockdep class for info_exist_lock" failed to apply to 6.12-stable tree

[gregkh]

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x 9910159f06590c17df4fbddedaabb4c0201cc4cb
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026012655-stipend-xbox-ead1@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 9910159f06590c17df4fbddedaabb4c0201cc4cb Mon Sep 17 00:00:00 2001
From: Rasmus Villemoes <ravi@prevas.dk>
Date: Mon, 15 Dec 2025 14:17:23 +0100
Subject: [PATCH] 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 <ravi@prevas.dk>
Reviewed-by: Peter Rosin <peda@axentia.se>
Cc: <stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index f69deefcfb6f..117ffad4f376 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -1657,6 +1657,7 @@ static void iio_dev_release(struct device *device)
 	mutex_destroy(&iio_dev_opaque->info_exist_lock);
 	mutex_destroy(&iio_dev_opaque->mlock);
 
+	lockdep_unregister_key(&iio_dev_opaque->info_exist_key);
 	lockdep_unregister_key(&iio_dev_opaque->mlock_key);
 
 	ida_free(&iio_ida, iio_dev_opaque->id);
@@ -1717,9 +1718,10 @@ struct iio_dev *iio_device_alloc(struct device *parent, int sizeof_priv)
 	INIT_LIST_HEAD(&iio_dev_opaque->ioctl_handlers);
 
 	lockdep_register_key(&iio_dev_opaque->mlock_key);
+	lockdep_register_key(&iio_dev_opaque->info_exist_key);
 
 	mutex_init_with_key(&iio_dev_opaque->mlock, &iio_dev_opaque->mlock_key);
-	mutex_init(&iio_dev_opaque->info_exist_lock);
+	mutex_init_with_key(&iio_dev_opaque->info_exist_lock, &iio_dev_opaque->info_exist_key);
 
 	indio_dev->dev.parent = parent;
 	indio_dev->dev.type = &iio_device_type;
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;

[PATCH 6.12.y 1/3] iio: core: add missing mutex_destroy in iio_dev_release()

[Sasha Levin]

From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

[ Upstream commit f5d203467a31798191365efeb16cd619d2c8f23a ]

Add missing mutex_destroy() call in iio_dev_release() to properly
clean up the mutex initialized in iio_device_alloc(). Ensure proper
resource cleanup and follows kernel practices.

Found by code review.

While at it, create a lockdep key before mutex initialisation.
This will help with converting it to the better API in the future.

Fixes: 847ec80bbaa7 ("Staging: IIO: core support for device registration and management")
Fixes: ac917a81117c ("staging:iio:core set the iio_dev.info pointer to null on unregister under lock.")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Stable-dep-of: 9910159f0659 ("iio: core: add separate lockdep class for info_exist_lock")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/iio/industrialio-core.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 6a6568d4a2cb3..43b842a062271 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -1628,6 +1628,9 @@ static void iio_dev_release(struct device *device)
 
 	iio_device_detach_buffers(indio_dev);
 
+	mutex_destroy(&iio_dev_opaque->info_exist_lock);
+	mutex_destroy(&iio_dev_opaque->mlock);
+
 	lockdep_unregister_key(&iio_dev_opaque->mlock_key);
 
 	ida_free(&iio_ida, iio_dev_opaque->id);
@@ -1672,8 +1675,7 @@ struct iio_dev *iio_device_alloc(struct device *parent, int sizeof_priv)
 	indio_dev->dev.type = &iio_device_type;
 	indio_dev->dev.bus = &iio_bus_type;
 	device_initialize(&indio_dev->dev);
-	mutex_init(&iio_dev_opaque->mlock);
-	mutex_init(&iio_dev_opaque->info_exist_lock);
+
 	INIT_LIST_HEAD(&iio_dev_opaque->channel_attr_list);
 
 	iio_dev_opaque->id = ida_alloc(&iio_ida, GFP_KERNEL);
@@ -1696,6 +1698,9 @@ struct iio_dev *iio_device_alloc(struct device *parent, int sizeof_priv)
 	lockdep_register_key(&iio_dev_opaque->mlock_key);
 	lockdep_set_class(&iio_dev_opaque->mlock, &iio_dev_opaque->mlock_key);
 
+	mutex_init(&iio_dev_opaque->mlock);
+	mutex_init(&iio_dev_opaque->info_exist_lock);
+
 	return indio_dev;
 }
 EXPORT_SYMBOL(iio_device_alloc);
-- 
2.51.0

[PATCH 6.12.y 2/3] iio: core: Replace lockdep_set_class() + mutex_init() by combined call

[Sasha Levin]

From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

[ Upstream commit c76ba4b2644424b8dbacee80bb40991eac29d39e ]

Replace lockdep_set_class() + mutex_init() by combined call
mutex_init_with_key().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Stable-dep-of: 9910159f0659 ("iio: core: add separate lockdep class for info_exist_lock")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/iio/industrialio-core.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 43b842a062271..f08211730ca20 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -1696,9 +1696,8 @@ struct iio_dev *iio_device_alloc(struct device *parent, int sizeof_priv)
 	INIT_LIST_HEAD(&iio_dev_opaque->ioctl_handlers);
 
 	lockdep_register_key(&iio_dev_opaque->mlock_key);
-	lockdep_set_class(&iio_dev_opaque->mlock, &iio_dev_opaque->mlock_key);
 
-	mutex_init(&iio_dev_opaque->mlock);
+	mutex_init_with_key(&iio_dev_opaque->mlock, &iio_dev_opaque->mlock_key);
 	mutex_init(&iio_dev_opaque->info_exist_lock);
 
 	return indio_dev;
-- 
2.51.0

[PATCH 6.12.y 3/3] iio: core: add separate lockdep class for info_exist_lock

[Sasha Levin]

From: Rasmus Villemoes <ravi@prevas.dk>

[ Upstream commit 9910159f06590c17df4fbddedaabb4c0201cc4cb ]

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 <ravi@prevas.dk>
Reviewed-by: Peter Rosin <peda@axentia.se>
Cc: <stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/iio/industrialio-core.c | 4 +++-
 include/linux/iio/iio-opaque.h  | 2 ++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index f08211730ca20..e7761b7d25a74 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -1631,6 +1631,7 @@ static void iio_dev_release(struct device *device)
 	mutex_destroy(&iio_dev_opaque->info_exist_lock);
 	mutex_destroy(&iio_dev_opaque->mlock);
 
+	lockdep_unregister_key(&iio_dev_opaque->info_exist_key);
 	lockdep_unregister_key(&iio_dev_opaque->mlock_key);
 
 	ida_free(&iio_ida, iio_dev_opaque->id);
@@ -1696,9 +1697,10 @@ struct iio_dev *iio_device_alloc(struct device *parent, int sizeof_priv)
 	INIT_LIST_HEAD(&iio_dev_opaque->ioctl_handlers);
 
 	lockdep_register_key(&iio_dev_opaque->mlock_key);
+	lockdep_register_key(&iio_dev_opaque->info_exist_key);
 
 	mutex_init_with_key(&iio_dev_opaque->mlock, &iio_dev_opaque->mlock_key);
-	mutex_init(&iio_dev_opaque->info_exist_lock);
+	mutex_init_with_key(&iio_dev_opaque->info_exist_lock, &iio_dev_opaque->info_exist_key);
 
 	return indio_dev;
 }
diff --git a/include/linux/iio/iio-opaque.h b/include/linux/iio/iio-opaque.h
index 5aec3945555bf..0e184cd5d6acc 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;
-- 
2.51.0