6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jeongjun Park aha310510@gmail.com
[ Upstream commit 2efe41234dbd0a83fdb7cd38226c2f70039a2cd3 ]
syzbot reported the following ABBA deadlock:
CPU0 CPU1 ---- ---- n_vclocks_store() lock(&ptp->n_vclocks_mux) [1] (physical clock) pc_clock_adjtime() lock(&clk->rwsem) [2] (physical clock) ... ptp_clock_freerun() ptp_vclock_in_use() lock(&ptp->n_vclocks_mux) [3] (physical clock) ptp_clock_unregister() posix_clock_unregister() lock(&clk->rwsem) [4] (virtual clock)
Since ptp virtual clock is registered only under ptp physical clock, both ptp_clock and posix_clock must be physical clocks for ptp_vclock_in_use() to lock &ptp->n_vclocks_mux and check ptp->n_vclocks.
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@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=7cfb66a237c4a5fb22ad Fixes: 73f37068d540 ("ptp: support ptp physical/virtual clocks conversion") Signed-off-by: Jeongjun Park aha310510@gmail.com Acked-by: Richard Cochran richardcochran@gmail.com Reviewed-by: Vladimir Oltean vladimir.oltean@nxp.com Link: https://patch.msgid.link/20250728062649.469882-1-aha310510@gmail.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/ptp/ptp_private.h | 5 +++++ drivers/ptp/ptp_vclock.c | 7 +++++++ 2 files changed, 12 insertions(+)
diff --git a/drivers/ptp/ptp_private.h b/drivers/ptp/ptp_private.h index a54124269c2f..3fbd1d68a9bc 100644 --- a/drivers/ptp/ptp_private.h +++ b/drivers/ptp/ptp_private.h @@ -20,6 +20,11 @@ #define PTP_BUF_TIMESTAMPS 30 #define PTP_DEFAULT_MAX_VCLOCKS 20
+enum { + PTP_LOCK_PHYSICAL = 0, + PTP_LOCK_VIRTUAL, +}; + struct timestamp_event_queue { struct ptp_extts_event buf[PTP_MAX_TIMESTAMPS]; int head; diff --git a/drivers/ptp/ptp_vclock.c b/drivers/ptp/ptp_vclock.c index dcf752c9e045..7d08ff3b30fc 100644 --- a/drivers/ptp/ptp_vclock.c +++ b/drivers/ptp/ptp_vclock.c @@ -154,6 +154,11 @@ static long ptp_vclock_refresh(struct ptp_clock_info *ptp) return PTP_VCLOCK_REFRESH_INTERVAL; }
+static void ptp_vclock_set_subclass(struct ptp_clock *ptp) +{ + lockdep_set_subclass(&ptp->clock.rwsem, PTP_LOCK_VIRTUAL); +} + static const struct ptp_clock_info ptp_vclock_info = { .owner = THIS_MODULE, .name = "ptp virtual clock", @@ -213,6 +218,8 @@ struct ptp_vclock *ptp_vclock_register(struct ptp_clock *pclock) return NULL; }
+ ptp_vclock_set_subclass(vclock->clock); + timecounter_init(&vclock->tc, &vclock->cc, 0); ptp_schedule_worker(vclock->clock, PTP_VCLOCK_REFRESH_INTERVAL);