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comedi: Reinit dev->spinlock between attachments to low-level drivers

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`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 25436dc9d8 ("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: ed9eccbe89 ("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>
This commit is contained in:
Ian Abbott
2026-02-25 13:24:27 +00:00
committed by Greg Kroah-Hartman
parent cc797d4821
commit 4b9a9a6d71
1 changed files with 8 additions and 0 deletions
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8
drivers/comedi/drivers.c
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@@ -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;