If an IIO driver uses callbacks from another IIO driver and calls
iio_channel_start_all_cb() from one of its buffer setup ops, then
lockdep complains due to the lock nesting, as in the below example with
lmp91000. Since the locks are being taken on different IIO devices,
there is no actual deadlock, so add lock nesting annotation to silence
the spurious warning.
============================================
WARNING: possible recursive locking detected
6.0.0-rc1+ #10 Not tainted
--------------------------------------------
python3/23 is trying to acquire lock:
0000000064c944c0 (&indio_dev->mlock){+.+.}-{3:3}, at: iio_update_buffers+0x62/0x180
but task is already holding lock:
00000000636b64c0 (&indio_dev->mlock){+.+.}-{3:3}, at: enable_store+0x4d/0x100
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&indio_dev->mlock);
lock(&indio_dev->mlock);
*** DEADLOCK ***
May be due to missing lock nesting notation
5 locks held by python3/23:
#0: 00000000636b5420 (sb_writers#5){.+.+}-{0:0}, at: ksys_write+0x67/0x100
#1: 0000000064c19280 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x13a/0x270
#2: 0000000064c3d9e0 (kn->active#14){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x149/0x270
#3: 00000000636b64c0 (&indio_dev->mlock){+.+.}-{3:3}, at: enable_store+0x4d/0x100
#4: 0000000064c945c8 (&iio_dev_opaque->info_exist_lock){+.+.}-{3:3}, at: iio_update_buffers+0x4f/0x180
stack backtrace:
CPU: 0 PID: 23 Comm: python3 Not tainted 6.0.0-rc1+ #10
Call Trace:
dump_stack+0x1a/0x1c
__lock_acquire.cold+0x407/0x42d
lock_acquire+0x1ed/0x310
__mutex_lock+0x72/0xde0
mutex_lock_nested+0x1d/0x20
iio_update_buffers+0x62/0x180
iio_channel_start_all_cb+0x1c/0x20 [industrialio_buffer_cb]
lmp91000_buffer_postenable+0x1b/0x20 [lmp91000]
__iio_update_buffers+0x50b/0xd80
enable_store+0x81/0x100
dev_attr_store+0xf/0x20
sysfs_kf_write+0x4c/0x70
kernfs_fop_write_iter+0x179/0x270
new_sync_write+0x99/0x120
vfs_write+0x2c1/0x470
ksys_write+0x67/0x100
sys_write+0x10/0x20
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>
---
drivers/iio/industrialio-buffer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
index acc2b6c05d57..27868ed092d0 100644
--- a/drivers/iio/industrialio-buffer.c
+++ b/drivers/iio/industrialio-buffer.c
@@ -1255,7 +1255,7 @@ int iio_update_buffers(struct iio_dev *indio_dev,
return -EINVAL;
mutex_lock(&iio_dev_opaque->info_exist_lock);
- mutex_lock(&indio_dev->mlock);
+ mutex_lock_nested(&indio_dev->mlock, SINGLE_DEPTH_NESTING);
if (insert_buffer && iio_buffer_is_active(insert_buffer))
insert_buffer = NULL;
--
2.34.1
