On Tue, Jun 25, 2024 at 07:38:15AM -0700, Paul E. McKenney wrote: > On Thu, Jun 20, 2024 at 10:54:34PM +0000, Carlos Llamas wrote: > > From: Zhiguo Niu <zhiguo.niu@xxxxxxxxxx> > > > > There is a deadlock scenario between lockdep and rcu when > > rcu nocb feature is enabled, just as following call stack: > > I have pulled this into -rcu for further review and testing. > > If someone else (for example, the lockdep folks) would like to take this: > > Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > FWIW, I add this patch and another one [1] to my tree: git://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git lockdep (based on today's tip/locking/core) I figured I have time to handle lockdep-only patches, which shouldn't be a lot. So Ingo & Peter, I'm happy to help. If you need me to pick up lockdep patches and send a PR against tip/master or tip/locking/core, please let me know. Regards, Boqun [1]: https://lore.kernel.org/all/20240528120008.403511-2-thorsten.blum@xxxxxxxxxx/ > > rcuop/x > > -000|queued_spin_lock_slowpath(lock = 0xFFFFFF817F2A8A80, val = ?) > > -001|queued_spin_lock(inline) // try to hold nocb_gp_lock > > -001|do_raw_spin_lock(lock = 0xFFFFFF817F2A8A80) > > -002|__raw_spin_lock_irqsave(inline) > > -002|_raw_spin_lock_irqsave(lock = 0xFFFFFF817F2A8A80) > > -003|wake_nocb_gp_defer(inline) > > -003|__call_rcu_nocb_wake(rdp = 0xFFFFFF817F30B680) > > -004|__call_rcu_common(inline) > > -004|call_rcu(head = 0xFFFFFFC082EECC28, func = ?) > > -005|call_rcu_zapped(inline) > > -005|free_zapped_rcu(ch = ?)// hold graph lock > > -006|rcu_do_batch(rdp = 0xFFFFFF817F245680) > > -007|nocb_cb_wait(inline) > > -007|rcu_nocb_cb_kthread(arg = 0xFFFFFF817F245680) > > -008|kthread(_create = 0xFFFFFF80803122C0) > > -009|ret_from_fork(asm) > > > > rcuop/y > > -000|queued_spin_lock_slowpath(lock = 0xFFFFFFC08291BBC8, val = 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 = 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 = 0xFFFFFF817F2A8680) > > -007|__call_rcu_common(inline) > > -007|call_rcu(head = 0xFFFFFFC0822E0B58, func = ?) > > -008|call_rcu_hurry(inline) > > -008|rcu_sync_call(inline) > > -008|rcu_sync_func(rhp = 0xFFFFFFC0822E0B58) > > -009|rcu_do_batch(rdp = 0xFFFFFF817F266680) > > -010|nocb_cb_wait(inline) > > -010|rcu_nocb_cb_kthread(arg = 0xFFFFFF817F266680) > > -011|kthread(_create = 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@xxxxxxxxxxxxxxx > > Cc: Boqun Feng <boqun.feng@xxxxxxxxx> > > Cc: Waiman Long <longman@xxxxxxxxxx> > > Cc: Carlos Llamas <cmllamas@xxxxxxxxxx> > > Cc: Bart Van Assche <bvanassche@xxxxxxx> > > Signed-off-by: Zhiguo Niu <zhiguo.niu@xxxxxxxxxx> > > Signed-off-by: Xuewen Yan <xuewen.yan@xxxxxxxxxx> > > Reviewed-by: Boqun Feng <boqun.feng@xxxxxxxxx> > > Reviewed-by: Waiman Long <longman@xxxxxxxxxx> > > Reviewed-by: Carlos Llamas <cmllamas@xxxxxxxxxx> > > Reviewed-by: Bart Van Assche <bvanassche@xxxxxxx> > > Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx> > > --- > > 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); > > > > /* > > - * 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()); > > > > if (list_empty(&pf->zapped)) > > - return; > > + return false; > > > > if (delayed_free.scheduled) > > - return; > > + return false; > > > > delayed_free.scheduled = true; > > > > WARN_ON_ONCE(delayed_free.pf + delayed_free.index != pf); > > delayed_free.index ^= 1; > > > > - call_rcu(&delayed_free.rcu_head, free_zapped_rcu); > > + return true; > > } > > > > /* 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; > > > > if (WARN_ON_ONCE(ch != &delayed_free.rcu_head)) > > return; > > @@ -6239,14 +6242,18 @@ static void free_zapped_rcu(struct rcu_head *ch) > > pf = delayed_free.pf + (delayed_free.index ^ 1); > > __free_zapped_classes(pf); > > delayed_free.scheduled = false; > > + need_callback = > > + prepare_call_rcu_zapped(delayed_free.pf + delayed_free.index); > > + lockdep_unlock(); > > + raw_local_irq_restore(flags); > > > > /* > > - * 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); > > > > - lockdep_unlock(); > > - raw_local_irq_restore(flags); > > } > > > > /* > > @@ -6286,6 +6293,7 @@ static void lockdep_free_key_range_reg(void *start, unsigned long size) > > { > > struct pending_free *pf; > > unsigned long flags; > > + bool need_callback; > > > > init_data_structures_once(); > > > > @@ -6293,10 +6301,11 @@ static void lockdep_free_key_range_reg(void *start, unsigned long size) > > lockdep_lock(); > > pf = get_pending_free(); > > __lockdep_free_key_range(pf, start, size); > > - call_rcu_zapped(pf); > > + need_callback = 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 = false; > > > > raw_local_irq_save(flags); > > locked = graph_lock(); > > @@ -6398,11 +6408,13 @@ static void lockdep_reset_lock_reg(struct lockdep_map *lock) > > > > pf = get_pending_free(); > > __lockdep_reset_lock(pf, lock); > > - call_rcu_zapped(pf); > > + need_callback = prepare_call_rcu_zapped(pf); > > > > graph_unlock(); > > out_irq: > > raw_local_irq_restore(flags); > > + if (need_callback) > > + call_rcu(&delayed_free.rcu_head, free_zapped_rcu); > > } > > > > /* > > @@ -6446,6 +6458,7 @@ void lockdep_unregister_key(struct lock_class_key *key) > > struct pending_free *pf; > > unsigned long flags; > > bool found = false; > > + bool need_callback = false; > > > > might_sleep(); > > > > @@ -6466,11 +6479,14 @@ void lockdep_unregister_key(struct lock_class_key *key) > > if (found) { > > pf = get_pending_free(); > > __lockdep_free_key_range(pf, key, 1); > > - call_rcu_zapped(pf); > > + need_callback = 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 until is_dynamic_key() has finished accessing k->hash_entry. */ > > synchronize_rcu(); > > } > > -- > > 2.45.2.741.gdbec12cfda-goog > >
