linux-kernel - RE: [PATCH] srcu: Fix flush sup work warning in cleanup_srcu

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Message-ID: <PH0PR11MB588087645FE02C9F2C113CC8DA869@PH0PR11MB5880.namprd11.prod.outlook.com>
Date:   Wed, 22 Mar 2023 01:15:02 +0000
From:   "Zhang, Qiang1" <qiang1.zhang@...el.com>
To:     "paulmck@...nel.org" <paulmck@...nel.org>
CC:     "frederic@...nel.org" <frederic@...nel.org>,
        "joel@...lfernandes.org" <joel@...lfernandes.org>,
        "rcu@...r.kernel.org" <rcu@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] srcu: Fix flush sup work warning in cleanup_srcu_struct()

> 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@...el.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.

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
>