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Jeongjun Park
54f8f98665
[ Upstream commit2efe41234d] 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:73f37068d5("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>