Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 23 Mar 2023 20:31:23 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     "Zhang, Qiang1" <qiang1.zhang@intel.com>
Cc:     "frederic@kernel.org" <frederic@kernel.org>,
        "joel@joelfernandes.org" <joel@joelfernandes.org>,
        "rcu@vger.kernel.org" <rcu@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "qiang.zhang1211@gmail.com" <qiang.zhang1211@gmail.com>
Subject: Re: [PATCH v2] srcu: Fix flush srcu structure's->sup work warning in
 cleanup_srcu_struct()
Message-ID: <baf071c3-142c-4886-aea5-6b6ef2ff3ade@paulmck-laptop>
Reply-To: paulmck@kernel.org
References: <20230323134621.336832-1-qiang1.zhang@intel.com>
 <f18cad71-38f0-411d-9dc7-bda52d1d5a3a@paulmck-laptop>
 <PH0PR11MB58803F01B73914E1D7A052F5DA849@PH0PR11MB5880.namprd11.prod.outlook.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <PH0PR11MB58803F01B73914E1D7A052F5DA849@PH0PR11MB5880.namprd11.prod.outlook.com>
Precedence: bulk

On Fri, Mar 24, 2023 at 02:20:18AM +0000, Zhang, Qiang1 wrote:
> Cc:  my personal email qiang.zhang1211@gmail.com
> 
> > When unloading rcutorture kmod will trigger the following callstack:
> > 
> > insmod rcutorture.ko
> > rmmod rcutorture.ko
> > 
> > [  209.437327] WARNING: CPU: 0 PID: 508 at kernel/workqueue.c:3167 __flush_work+0x50a/0x540
> > [  209.437346] Modules linked in: rcutorture(-) torture [last unloaded: rcutorture]
> > [  209.437382] CPU: 0 PID: 508 Comm: rmmod Tainted: G  W  6.3.0-rc1-yocto-standard+
> > [  209.437406] RIP: 0010:__flush_work+0x50a/0x540
> > .....
> > [  209.437758]  flush_delayed_work+0x36/0x90
> > [  209.437776]  cleanup_srcu_struct+0x68/0x2e0
> > [  209.437817]  srcu_module_notify+0x71/0x140
> > [  209.437854]  blocking_notifier_call_chain+0x9d/0xd0
> > [  209.437880]  __x64_sys_delete_module+0x223/0x2e0
> > [  209.438046]  do_syscall_64+0x43/0x90
> > [  209.438062]  entry_SYSCALL_64_after_hwframe+0x72/0xdc
> > 
> > flush_delayed_work()
> > ->__flush_work()
> >    ->if (WARN_ON(!work->func))
> >         return false;
> > 
> > For srcu objects defined with DEFINE_SRCU() or DEFINE_STATIC_SRCU(),
> > when compiling and loading as modules, the srcu_module_coming() is
> > invoked, allocate memory for srcu structure's->sda and initialize
> > sda structure, due to not fully initialize srcu structure's->sup,
> > so at this time the sup structure's->work.work.func is null, if not
> > invoke init_srcu_struct_fields() before unloading modules, the
> > __flush_work() be invoked in srcu_module_going() and find work->func
> > is empty, will raise the warning above.
> > 
> > This commit add the check of srcu_sup structure's->srcu_gp_seq_needed
> > to determine whether the check_init_srcu_struct() has been invoked to
> > initialize srcu objects in srcu_module_going(), if not initialize, there
> > are no pending or running works, so there is no need to flush, only invoke
> > free_percpu() to release srcu structure's->sda.
> > 
> > Co-developed-by: Paul E. McKenney <paulmck@kernel.org>
> >
> >Thank you for the testing, bug-finding, and problem-solving!
> >
> >In theory, you would need a Signed-off-by here from me as well, but
> >in practice bisectability means that this must be folded into this:
> >
> >e7c778489040 ("srcu: Use static init for statically allocated in-module srcu_struct")
> >	
> >This will of course be with attribution.
> >
> > Signed-off-by: Zqiang <qiang1.zhang@intel.com>
> >
> >But this is still a bit more complex than needed.  How about something
> >like this?
> 
> Agree,  from a logical point of view, this is more rigorous????.

And I finally got around to doing some modprobe/rmmod testing myself,
and it passes eleven cycles.

May I add your Tested-by to the series?

							Thanx, Paul

> Thanks
> Zqiang
> 
> >
> >							Thanx, Paul
> >
> >------------------------------------------------------------------------
> >
> >/* Initialize any global-scope srcu_struct structures used by this module. */
> >static int srcu_module_coming(struct module *mod)
> >{
> >	int i;
> >	struct srcu_struct *ssp;
> >	struct srcu_struct **sspp = mod->srcu_struct_ptrs;
> >
> >	for (i = 0; i < mod->num_srcu_structs; i++) {
> >		ssp = *(sspp++);
> >		ssp->sda = alloc_percpu(struct srcu_data);
> >		if (WARN_ON_ONCE(!ssp->sda))
> >			return -ENOMEM;
> >	}
> >	return 0;
> >}
> >
> >/* Clean up any global-scope srcu_struct structures used by this module. */
> >static void srcu_module_going(struct module *mod)
> >{
> >	int i;
> >	struct srcu_struct *ssp;
> >	struct srcu_struct **sspp = mod->srcu_struct_ptrs;
> >
> >	for (i = 0; i < mod->num_srcu_structs; i++) {
> >		ssp = *(sspp++);
> >		if (!rcu_seq_state(smp_load_acquire(&ssp->srcu_sup->srcu_gp_seq_needed)) &&
> >		    !WARN_ON_ONCE(!ssp->srcu_sup->sda_is_static))
> >				cleanup_srcu_struct(ssp);
> >		free_percpu(ssp->sda);
> >	}
> >}