[PATCH 6.6 118/160] comedi: Reinit dev->spinlock between attachments to low-level drivers

Greg Kroah-Hartman
2026-04-08T18:25:26Z

From: Ian Abbott <abbotti@mev.co.uk>

commit 4b9a9a6d71e3e252032f959fb3895a33acb5865c upstream.

`struct comedi_device` is the main controlling structure for a COMEDI
device created by the COMEDI subsystem. It contains a member `spinlock`
containing a spin-lock that is initialized by the COMEDI subsystem, but
is reserved for use by a low-level driver attached to the COMEDI device
(at least since commit 25436dc9d84f ("Staging: comedi: remove RT
code")).

Some COMEDI devices (those created on initialization of the COMEDI
subsystem when the "comedi.comedi_num_legacy_minors" parameter is
non-zero) can be attached to different low-level drivers over their
lifetime using the `COMEDI_DEVCONFIG` ioctl command. This can result in
inconsistent lock states being reported when there is a mismatch in the
spin-lock locking levels used by each low-level driver to which the
COMEDI device has been attached. Fix it by reinitializing
`dev->spinlock` before calling the low-level driver's `attach` function
pointer if `CONFIG_LOCKDEP` is enabled.

Reported-by: syzbot+cc9f7f4a7df09f53c4a4@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=cc9f7f4a7df09f53c4a4
Fixes: ed9eccbe8970 ("Staging: add comedi core")
Cc: stable <stable@kernel.org>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://patch.msgid.link/20260225132427.86578-1-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/comedi/drivers.c | 8 ++++++++
1 file changed, 8 insertions(+)

--- a/drivers/comedi/drivers.c
+++ b/drivers/comedi/drivers.c
@@ -1000,6 +1000,14 @@ int comedi_device_attach(struct comedi_d
ret = -EIO;
goto out;
}
+ if (IS_ENABLED(CONFIG_LOCKDEP)) {
+ /*
+ * dev->spinlock is for private use by the attached low-level
+ * driver. Reinitialize it to stop lock-dependency tracking
+ * between attachments to different low-level drivers.
+ */
+ spin_lock_init(&dev->spinlock);
+ }
dev->driver = driv;
dev->board_name = dev->board_ptr ? *(const char **)dev->board_ptr
: dev->driver->driver_name;