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McKenney" , Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long , Boqun Feng , Bart Van Assche Cc: Andrew Morton , John Stultz , Joel Fernandes , linux-kernel@vger.kernel.org, kernel-team@android.com, Zhiguo Niu , stable@vger.kernel.org, Carlos Llamas , Xuewen Yan , Ingo Molnar Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Zhiguo Niu There is a deadlock scenario between lockdep and rcu when rcu nocb feature is enabled, just as following call stack: rcuop/x -000|queued_spin_lock_slowpath(lock =3D 0xFFFFFF817F2A8A80, val =3D ?) -001|queued_spin_lock(inline) // try to hold nocb_gp_lock -001|do_raw_spin_lock(lock =3D 0xFFFFFF817F2A8A80) -002|__raw_spin_lock_irqsave(inline) -002|_raw_spin_lock_irqsave(lock =3D 0xFFFFFF817F2A8A80) -003|wake_nocb_gp_defer(inline) -003|__call_rcu_nocb_wake(rdp =3D 0xFFFFFF817F30B680) -004|__call_rcu_common(inline) -004|call_rcu(head =3D 0xFFFFFFC082EECC28, func =3D ?) -005|call_rcu_zapped(inline) -005|free_zapped_rcu(ch =3D ?)// hold graph lock -006|rcu_do_batch(rdp =3D 0xFFFFFF817F245680) -007|nocb_cb_wait(inline) -007|rcu_nocb_cb_kthread(arg =3D 0xFFFFFF817F245680) -008|kthread(_create =3D 0xFFFFFF80803122C0) -009|ret_from_fork(asm) rcuop/y -000|queued_spin_lock_slowpath(lock =3D 0xFFFFFFC08291BBC8, val =3D 0) -001|queued_spin_lock() -001|lockdep_lock() -001|graph_lock() // try to hold graph lock -002|lookup_chain_cache_add() -002|validate_chain() -003|lock_acquire -004|_raw_spin_lock_irqsave(lock =3D 0xFFFFFF817F211D80) -005|lock_timer_base(inline) -006|mod_timer(inline) -006|wake_nocb_gp_defer(inline)// hold nocb_gp_lock -006|__call_rcu_nocb_wake(rdp =3D 0xFFFFFF817F2A8680) -007|__call_rcu_common(inline) -007|call_rcu(head =3D 0xFFFFFFC0822E0B58, func =3D ?) -008|call_rcu_hurry(inline) -008|rcu_sync_call(inline) -008|rcu_sync_func(rhp =3D 0xFFFFFFC0822E0B58) -009|rcu_do_batch(rdp =3D 0xFFFFFF817F266680) -010|nocb_cb_wait(inline) -010|rcu_nocb_cb_kthread(arg =3D 0xFFFFFF817F266680) -011|kthread(_create =3D 0xFFFFFF8080363740) -012|ret_from_fork(asm) rcuop/x and rcuop/y are rcu nocb threads with the same nocb gp thread. This patch release the graph lock before lockdep call_rcu. Fixes: a0b0fd53e1e6 ("locking/lockdep: Free lock classes that are no longer= in use") Cc: stable@vger.kernel.org Cc: Boqun Feng Cc: Waiman Long Cc: Carlos Llamas Cc: Bart Van Assche Signed-off-by: Zhiguo Niu Signed-off-by: Xuewen Yan Reviewed-by: Boqun Feng Reviewed-by: Waiman Long Reviewed-by: Carlos Llamas Reviewed-by: Bart Van Assche Signed-off-by: Carlos Llamas Acked-by: Paul E. McKenney --- kernel/locking/lockdep.c | 48 ++++++++++++++++++++++++++-------------- 1 file changed, 32 insertions(+), 16 deletions(-) diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 151bd3de5936..3468d8230e5f 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -6184,25 +6184,27 @@ static struct pending_free *get_pending_free(void) static void free_zapped_rcu(struct rcu_head *cb); =20 /* - * Schedule an RCU callback if no RCU callback is pending. Must be called = with - * the graph lock held. - */ -static void call_rcu_zapped(struct pending_free *pf) +* See if we need to queue an RCU callback, must called with +* the lockdep lock held, returns false if either we don't have +* any pending free or the callback is already scheduled. +* Otherwise, a call_rcu() must follow this function call. +*/ +static bool prepare_call_rcu_zapped(struct pending_free *pf) { WARN_ON_ONCE(inside_selftest()); =20 if (list_empty(&pf->zapped)) - return; + return false; =20 if (delayed_free.scheduled) - return; + return false; =20 delayed_free.scheduled =3D true; =20 WARN_ON_ONCE(delayed_free.pf + delayed_free.index !=3D pf); delayed_free.index ^=3D 1; =20 - call_rcu(&delayed_free.rcu_head, free_zapped_rcu); + return true; } =20 /* The caller must hold the graph lock. May be called from RCU context. */ @@ -6228,6 +6230,7 @@ static void free_zapped_rcu(struct rcu_head *ch) { struct pending_free *pf; unsigned long flags; + bool need_callback; =20 if (WARN_ON_ONCE(ch !=3D &delayed_free.rcu_head)) return; @@ -6239,14 +6242,18 @@ static void free_zapped_rcu(struct rcu_head *ch) pf =3D delayed_free.pf + (delayed_free.index ^ 1); __free_zapped_classes(pf); delayed_free.scheduled =3D false; + need_callback =3D + prepare_call_rcu_zapped(delayed_free.pf + delayed_free.index); + lockdep_unlock(); + raw_local_irq_restore(flags); =20 /* - * If there's anything on the open list, close and start a new callback. - */ - call_rcu_zapped(delayed_free.pf + delayed_free.index); + * If there's pending free and its callback has not been scheduled, + * queue an RCU callback. + */ + if (need_callback) + call_rcu(&delayed_free.rcu_head, free_zapped_rcu); =20 - lockdep_unlock(); - raw_local_irq_restore(flags); } =20 /* @@ -6286,6 +6293,7 @@ static void lockdep_free_key_range_reg(void *start, u= nsigned long size) { struct pending_free *pf; unsigned long flags; + bool need_callback; =20 init_data_structures_once(); =20 @@ -6293,10 +6301,11 @@ static void lockdep_free_key_range_reg(void *start,= unsigned long size) lockdep_lock(); pf =3D get_pending_free(); __lockdep_free_key_range(pf, start, size); - call_rcu_zapped(pf); + need_callback =3D prepare_call_rcu_zapped(pf); lockdep_unlock(); raw_local_irq_restore(flags); - + if (need_callback) + call_rcu(&delayed_free.rcu_head, free_zapped_rcu); /* * Wait for any possible iterators from look_up_lock_class() to pass * before continuing to free the memory they refer to. @@ -6390,6 +6399,7 @@ static void lockdep_reset_lock_reg(struct lockdep_map= *lock) struct pending_free *pf; unsigned long flags; int locked; + bool need_callback =3D false; =20 raw_local_irq_save(flags); locked =3D graph_lock(); @@ -6398,11 +6408,13 @@ static void lockdep_reset_lock_reg(struct lockdep_m= ap *lock) =20 pf =3D get_pending_free(); __lockdep_reset_lock(pf, lock); - call_rcu_zapped(pf); + need_callback =3D prepare_call_rcu_zapped(pf); =20 graph_unlock(); out_irq: raw_local_irq_restore(flags); + if (need_callback) + call_rcu(&delayed_free.rcu_head, free_zapped_rcu); } =20 /* @@ -6446,6 +6458,7 @@ void lockdep_unregister_key(struct lock_class_key *ke= y) struct pending_free *pf; unsigned long flags; bool found =3D false; + bool need_callback =3D false; =20 might_sleep(); =20 @@ -6466,11 +6479,14 @@ void lockdep_unregister_key(struct lock_class_key *= key) if (found) { pf =3D get_pending_free(); __lockdep_free_key_range(pf, key, 1); - call_rcu_zapped(pf); + need_callback =3D prepare_call_rcu_zapped(pf); } lockdep_unlock(); raw_local_irq_restore(flags); =20 + if (need_callback) + call_rcu(&delayed_free.rcu_head, free_zapped_rcu); + /* Wait until is_dynamic_key() has finished accessing k->hash_entry. */ synchronize_rcu(); } --=20 2.45.2.741.gdbec12cfda-goog