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[34.83.33.152]) by smtp.gmail.com with ESMTPSA id sg15-20020a17090b520f00b00293851b198csm12770pjb.56.2024.02.01.08.35.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Feb 2024 08:35:21 -0800 (PST) Date: Thu, 1 Feb 2024 16:35:17 +0000 From: Carlos Llamas To: Zhiguo Niu Cc: peterz@infradead.org, mingo@redhat.com, will@kernel.org, longman@redhat.com, boqun.feng@gmail.com, linux-kernel@vger.kernel.org, niuzhiguo84@gmail.com, ke.wang@unisoc.com, xuewen.yan@unisoc.com, Bart Van Assche Subject: Re: [PATCH V2] lockdep: fix deadlock issue between lockdep and rcu Message-ID: References: <1705477714-10467-1-git-send-email-zhiguo.niu@unisoc.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1705477714-10467-1-git-send-email-zhiguo.niu@unisoc.com> On Wed, Jan 17, 2024 at 03:48:34PM +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") This has a "Fixes" tag but I don't see Cc: stable. Does this need to be picked for stable branches? Or does tip branch does something special? Also, Cc: Bart Van Assche (blamed_fixes) just FYI. -- Carlos Llamas