Re: [PATCH net v4] ptp: prevent possible ABBA deadlock in ptp_clock_freerun()

[Richard Cochran]

On Mon, Jul 28, 2025 at 03:26:49PM +0900, Jeongjun Park wrote:

> However, when unregistering vclocks in n_vclocks_store(), the locking
> ptp->n_vclocks_mux is a physical clock lock, but clk->rwsem of
> ptp_clock_unregister() called through device_for_each_child_reverse()
> is a virtual clock lock.
> 
> Therefore, clk->rwsem used in CPU0 and clk->rwsem used in CPU1 are
> different locks, but in lockdep, a false positive occurs because the
> possibility of deadlock is determined through lock-class.
> 
> To solve this, lock subclass annotation must be added to the posix_clock
> rwsem of the vclock.
> 
> Reported-by: syzbot+7cfb66a237c4a5fb22ad@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=7cfb66a237c4a5fb22ad
> Fixes: 73f37068d540 ("ptp: support ptp physical/virtual clocks conversion")
> Signed-off-by: Jeongjun Park <aha310510@xxxxxxxxx>

Acked-by: Richard Cochran <richardcochran@xxxxxxxxx>