Re: [PATCH V3] lockdep: fix deadlock issue between lockdep and rcu

[Greg KH]

On Fri, Feb 02, 2024 at 07:55:48PM +0000, Carlos Llamas wrote:
> On Fri, Feb 02, 2024 at 04:14:36PM +0800, 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")
> > 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>
> > ---
> > changes of v3: correct code comments and add Cc tag.
> > changes of v2: update patch according to Boqun's suggestions.
> > ---
> 
> It seems v3 should have collected the review tags from Boqun and Waiman.
> Also, I'm actually Cc'ing stable here. I hope that is enough.
> FWIW, this looks fine to me.
> 
> Reviewed-by: Carlos Llamas <cmllamas@xxxxxxxxxx>


<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>