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Message-ID: <ZaFkKPDTpCTXdyvT@lothringen>
Date: Fri, 12 Jan 2024 17:09:12 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Zqiang <qiang.zhang1211@...il.com>
Cc: paulmck@...nel.org, quic_neeraju@...cinc.com, joel@...lfernandes.org,
rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu/nocb: Fix WARN_ON_ONCE() in the
rcu_nocb_bypass_lock()
On Wed, Jan 10, 2024 at 04:11:28PM +0800, Zqiang wrote:
> For the kernels built with CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y and
> CONFIG_RCU_LAZY=y, here are the following scenarios that will trigger
> WARN_ON_ONCE() in the rcu_nocb_bypass_lock() and rcu_nocb_wait_contended().
>
> CPU2 CPU11
> kthread
> rcu_nocb_cb_kthread ksys_write
> rcu_do_batch vfs_write
> rcu_torture_timer_cb proc_sys_write
> __kmem_cache_free proc_sys_call_handler
> kmemleak_free drop_caches_sysctl_handler
> delete_object_full drop_slab
> __delete_object shrink_slab
> put_object lazy_rcu_shrink_scan
> call_rcu rcu_nocb_flush_bypass
> __call_rcu_commn rcu_nocb_bypass_lock
> raw_spin_trylock(&rdp->nocb_bypass_lock) fail
> atomic_inc(&rdp->nocb_lock_contended);
> rcu_nocb_wait_contended WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
> WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended)) |
> |_ _ _ _ _ _ _ _ _ _same rdp and rdp->cpu != 11_ _ _ _ _ _ _ _ _ __|
>
> This commit therefore use the rcu_nocb_try_flush_bypass() instead of
> rcu_nocb_flush_bypass() in lazy_rcu_shrink_scan(), if the nocb_bypass
> queue is being flushed, the rcu_nocb_try_flush_bypass will return directly.
>
> Signed-off-by: Zqiang <qiang.zhang1211@...il.com>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
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