From 4b9a9a6d71e3e252032f959fb3895a33acb5865c Mon Sep 17 00:00:00 2001 From: Ian Abbott Date: Wed, 25 Feb 2026 13:24:27 +0000 Subject: [PATCH] comedi: Reinit dev->spinlock between attachments to low-level drivers `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 Signed-off-by: Ian Abbott Link: https://patch.msgid.link/20260225132427.86578-1-abbotti@mev.co.uk Signed-off-by: Greg Kroah-Hartman --- drivers/comedi/drivers.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/comedi/drivers.c b/drivers/comedi/drivers.c index db225a3bf012..5ab96b5eefd1 100644 --- a/drivers/comedi/drivers.c +++ b/drivers/comedi/drivers.c @@ -1063,6 +1063,14 @@ int comedi_device_attach(struct comedi_device *dev, struct comedi_devconfig *it) 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; -- 2.30.2