6.6-stable review patch. If anyone has any objections, please let me know.
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From: Jeongjun Park aha310510@gmail.com
[ Upstream commit 87f7ce260a3c838b49e1dc1ceedf1006795157a2 ]
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 aha310510@gmail.com Acked-by: Richard Cochran richardcochran@gmail.com Link: https://patch.msgid.link/20250520160717.7350-1-aha310510@gmail.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 b8d4f61f14be4..d0eb4555720eb 100644 --- a/drivers/ptp/ptp_private.h +++ b/drivers/ptp/ptp_private.h @@ -89,17 +89,7 @@ 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 */