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Date:   Wed, 22 Mar 2023 07:57:27 -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>
Subject: Re: [PATCH] srcu: Fix flush sup work warning in cleanup_srcu_struct()
Message-ID: <dc8b5a44-02ca-4e5a-bd4a-644af3e7c11e@paulmck-laptop>
Reply-To: paulmck@kernel.org
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On Wed, Mar 22, 2023 at 04:38:29AM +0000, Zhang, Qiang1 wrote:
> > > 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
> > > 
> > > 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->delaywork.func is null, if not 
> > > invoke init_srcu_struct_fields() before unloading modules, in 
> > > srcu_module_going() the __flush_work() find
> > > work->func is empty, will raise the warning above.
> > > 
> > > This commit add init_srcu_struct_fields() to initialize srcu 
> > > structure's->sup, in srcu_module_coming().
> > > 
> > > Signed-off-by: Zqiang <qiang1.zhang@intel.com>
> > >
> > >Good catch, and thank you for testing the in-module case!
> > >
> > >One question below...
> > >
> > >							Thanx, Paul
> > >
> > > ---
> > >  kernel/rcu/srcutree.c | 11 ++++++++---
> > >  1 file changed, 8 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 
> > > 1fb078abbdc9..42d8720e016c 100644
> > > --- a/kernel/rcu/srcutree.c
> > > +++ b/kernel/rcu/srcutree.c
> > > @@ -1921,7 +1921,8 @@ static int srcu_module_coming(struct module *mod)
> > >  		ssp->sda = alloc_percpu(struct srcu_data);
> > >  		if (WARN_ON_ONCE(!ssp->sda))
> > >  			return -ENOMEM;
> > > -		init_srcu_struct_data(ssp);
> > > +		if (WARN_ON_ONCE(init_srcu_struct_fields(ssp, true)))
> > > +			return -ENOMEM;
> > >
> > >Wouldn't it be better to simply delete the init_srcu_struct_data()?
> > >
> > >Then the first call to check_init_srcu_struct() would take care of 
> > >the initialization, just as for the non-module case.  Or am I missing 
> > >something subtle?
> > 
> > Hi Paul
> > 
> > Maybe the check_init_srcu_struct() is always not invoked, for example,
> > In rcutorture.c,   here is such a definition DEFINE_STATIC_SRCU(srcu_ctl),
> > but we use torture_type=rcu to test,  there will not be any interface 
> > calling
> > check_init_srcu_struct() to initialize srcu_ctl and set  
> > structure's->delaywork.func is process_srcu().
> > when we unload the rcutorture module, invoke cleanup_srcu_struct() to 
> > flush sup structure's->delaywork.func, due to the func pointer is not 
> > initialize, it's null, will trigger warning.
> > 
> > About kernel/workqueue.c:3167
> > 
> > __flush_work
> >      if (WARN_ON(!work->func))   <---------trigger waning
> > 	return false;
> > 
> > 
> > and  in  init_srcu_struct_fields(ssp, true), wil set 
> > srcu_sup->sda_is_static is true and set srcu_sup-> srcu_gp_seq_needed 
> > is zero,  after that when we call
> >  check_init_srcu_struct() again, it not be initialized again.
> >
> >
> >Good point!  In the non-module statically allocated case there is never a call to cleanup_srcu_struct().
> >
> >So suppose the code in srcu_module_coming() only did the alloc_percpu(), and then the
> >code in srcu_module_going() only did the the matching
> >free_percpu() instead of the current cleanup_srcu_struct()?
> 
> But in modules, for srcu objects defined with DEFINE_SRCU() or DEFINE_STATIC_SRCU(),
> when a module is unloaded, we usually don't call cleanup_srcu_struct() in the module
> unload function.
> If in srcu_module_going() only do free_percpu(), the srcu_sup->node memory maybe
> can not free and also lost the opportunity to refresh the running work.

But in the module case, isn't the srcu_sup->node also statically
allocated via the "static struct srcu_usage" declaration?

							Thanx, Paul

------------------------------------------------------------------------

#ifdef MODULE
# define __DEFINE_SRCU(name, is_static)								\
	static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage);	\
	is_static struct srcu_struct name = __SRCU_STRUCT_INIT_MODULE(name, name##_srcu_usage);	\
	extern struct srcu_struct * const __srcu_struct_##name;					\
	struct srcu_struct * const __srcu_struct_##name						\
		__section("___srcu_struct_ptrs") = &name
#else
# define __DEFINE_SRCU(name, is_static)								\
	static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data);				\
	static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage);	\
	is_static struct srcu_struct name =							\
		__SRCU_STRUCT_INIT(name, name##_srcu_usage, name##_srcu_data)
#endif

> Thanks
> Zqiang
> 
> 
> >
> >							Thanx, Paul
> >
> > Thanks
> > Zqiang
> > 
> > >
> > >It should also be possible to eliminate duplicate code between the 
> > >in-module and non-module statically allocated initialization cases, 
> > >come to think of it.
> > >
> > >  	}
> > >  	return 0;
> > >  }
> > > @@ -1931,9 +1932,13 @@ static void srcu_module_going(struct module 
> > > *mod)  {
> > >  	int i;
> > >  	struct srcu_struct **sspp = mod->srcu_struct_ptrs;
> > > +	struct srcu_struct *ssp;
> > >  
> > > -	for (i = 0; i < mod->num_srcu_structs; i++)
> > > -		cleanup_srcu_struct(*(sspp++));
> > > +	for (i = 0; i < mod->num_srcu_structs; i++) {
> > > +		ssp = *(sspp++);
> > > +		cleanup_srcu_struct(ssp);
> > > +		free_percpu(ssp->sda);
> > > +	}
> > >
> > >And good catch on another memory leak with this one, looks proper to 
> > >me.
> > >
> > >  }
> > >  
> > >  /* Handle one module, either coming or going. */
> > > --
> > > 2.25.1
> > >