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Wed, 17 Jan 2024 14:58:51 +0000 (UTC) Message-ID: Date: Wed, 17 Jan 2024 09:58:51 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V2] lockdep: fix deadlock issue between lockdep and rcu Content-Language: en-US To: Zhiguo Niu , peterz@infradead.org, mingo@redhat.com, will@kernel.org, boqun.feng@gmail.com Cc: linux-kernel@vger.kernel.org, niuzhiguo84@gmail.com, ke.wang@unisoc.com, xuewen.yan@unisoc.com References: <1705477714-10467-1-git-send-email-zhiguo.niu@unisoc.com> From: Waiman Long In-Reply-To: <1705477714-10467-1-git-send-email-zhiguo.niu@unisoc.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.2 On 1/17/24 02:48, Zhiguo Niu wrote: > 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 = 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") > Signed-off-by: Zhiguo Niu > Signed-off-by: Xuewen Yan > --- > changes of v2: update patch according to Boqun's suggestions. > --- > --- > kernel/locking/lockdep.c | 47 +++++++++++++++++++++++++++++++---------------- > 1 file changed, 31 insertions(+), 16 deletions(-) > > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > index 151bd3d..ddcaa69 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 +6242,17 @@ 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 anything on the open list, close and start a new callback. > + */ > + if (need_callback) > + call_rcu(&delayed_free.rcu_head, free_zapped_rcu); > > - lockdep_unlock(); > - raw_local_irq_restore(flags); > } > > /* > @@ -6286,6 +6292,7 @@ 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 +6300,11 @@ 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 +6398,7 @@ 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 +6407,13 @@ 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 +6457,7 @@ 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 +6478,14 @@ 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(); > } LGTM. Reviewed-by: Waiman Long