From 87f7ce260a3c838b49e1dc1ceedf1006795157a2 Mon Sep 17 00:00:00 2001 From: Jeongjun Park Date: Wed, 21 May 2025 01:07:17 +0900 Subject: [PATCH] ptp: remove ptp->n_vclocks check logic in ptp_vclock_in_use() There is no disagreement that we should check both ptp->is_virtual_clock and ptp->n_vclocks to check if the ptp virtual clock is in use. However, when we acquire ptp->n_vclocks_mux to read ptp->n_vclocks in ptp_vclock_in_use(), we observe a recursive lock in the call trace starting from n_vclocks_store(). ============================================ WARNING: possible recursive locking detected 6.15.0-rc6 #1 Not tainted -------------------------------------------- syz.0.1540/13807 is trying to acquire lock: ffff888035a24868 (&ptp->n_vclocks_mux){+.+.}-{4:4}, at: ptp_vclock_in_use drivers/ptp/ptp_private.h:103 [inline] ffff888035a24868 (&ptp->n_vclocks_mux){+.+.}-{4:4}, at: ptp_clock_unregister+0x21/0x250 drivers/ptp/ptp_clock.c:415 but task is already holding lock: ffff888030704868 (&ptp->n_vclocks_mux){+.+.}-{4:4}, at: n_vclocks_store+0xf1/0x6d0 drivers/ptp/ptp_sysfs.c:215 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&ptp->n_vclocks_mux); lock(&ptp->n_vclocks_mux); *** DEADLOCK *** .... ============================================ The best way to solve this is to remove the logic that checks ptp->n_vclocks in ptp_vclock_in_use(). The reason why this is appropriate is that any path that uses ptp->n_vclocks must unconditionally check if ptp->n_vclocks is greater than 0 before unregistering vclocks, and all functions are already written this way. And in the function that uses ptp->n_vclocks, we already get ptp->n_vclocks_mux before unregistering vclocks. Therefore, we need to remove the redundant check for ptp->n_vclocks in ptp_vclock_in_use() to prevent recursive locking. Fixes: 73f37068d540 ("ptp: support ptp physical/virtual clocks conversion") Signed-off-by: Jeongjun Park Acked-by: Richard Cochran Link: https://patch.msgid.link/20250520160717.7350-1-aha310510@gmail.com Signed-off-by: Jakub Kicinski --- drivers/ptp/ptp_private.h | 12 +----------- 1 file changed, 1 insertion(+), 11 deletions(-) diff --git a/drivers/ptp/ptp_private.h b/drivers/ptp/ptp_private.h index 18934e28469e..528d86a33f37 100644 --- a/drivers/ptp/ptp_private.h +++ b/drivers/ptp/ptp_private.h @@ -98,17 +98,7 @@ static inline int queue_cnt(const struct timestamp_event_queue *q) /* Check if ptp virtual clock is in use */ static inline bool ptp_vclock_in_use(struct ptp_clock *ptp) { - bool in_use = false; - - if (mutex_lock_interruptible(&ptp->n_vclocks_mux)) - return true; - - if (!ptp->is_virtual_clock && ptp->n_vclocks) - in_use = true; - - mutex_unlock(&ptp->n_vclocks_mux); - - return in_use; + return !ptp->is_virtual_clock; } /* Check if ptp clock shall be free running */ -- 2.39.5