On Mon, Nov 29, 2021 at 04:39:43PM +0100, Lukas Wunner wrote: > On Mon, Nov 29, 2021 at 01:19:34PM +0100, Hans de Goede wrote: > > Use down_read_nested() and down_write_nested() when taking the > > ctrl->reset_lock rw-sem, passing the PCI-device depth in the hierarchy > > as lock subclass parameter. This fixes the following false-positive lockdep > > report when unplugging a Lenovo X1C8 from a Lenovo 2nd gen TB3 dock: > [...] > > Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx> > > That's exactly what I had in mind, thanks. Hm, I found the notes that I took when I investigated Theodore's report: Using a subclass may be problematic because it's limited to a value < 8 (MAX_LOCKDEP_SUBCLASSES). If there's a hotplug port at a deeper level than 8 in the PCI hierarchy (can easily happen, Thunderbolt daisy chain allows up to 6 devices, each device contains a PCIe switch, so 2 levels per device), look_up_lock_class() in kernel/locking/lockdep.c will emit a BUG error message. It may be necessary to call lockdep_register_key() for each level or for each hotplug port and assign the lock with lockdep_set_class() (or ..._and_name() and use the dev_name()). It's these complications that made me put aside the problem back in the day. My apologies for not remembering them earlier. Thanks, Lukas
