linux-kernel - RE: [PATCH] rcu: Make vmalloc_dump_obj() call in a preemptible context

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Date:   Thu, 17 Nov 2022 05:20:06 +0000
From:   "Zhang, Qiang1" <qiang1.zhang@...el.com>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>,
        "paulmck@...nel.org" <paulmck@...nel.org>,
        "frederic@...nel.org" <frederic@...nel.org>,
        "joel@...lfernandes.org" <joel@...lfernandes.org>
CC:     "rcu@...r.kernel.org" <rcu@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] rcu: Make vmalloc_dump_obj() call in a preemptible
 context



On 2022/11/16 22:15, Zqiang wrote:
> Currently, the mem_dump_obj() is invoked in call_rcu(), the
>
>Plan to call mem_dump_obj() in rcu_do_batch().
>
> call_rcu() is maybe invoked in non-preemptive code segment,
> for object allocated from vmalloc(), the following scenarios
> may occur:
> 
> 	CPU 0
> tasks context
>    spin_lock(&vmap_area_lock)
>           Interrupt context
> 	      call_rcu()
> 		mem_dump_obj
>                   vmalloc_dump_obj
>                     spin_lock(&vmap_area_lock) <--deadlock
> 
> and for PREEMPT-RT kernel, the spinlock will convert to sleepable
> lock, it also make vmap_area_lock spinlock can not acquire in
> non-preemptive code segment. therefore, this commit make the
> vmalloc_dump_obj() call in a preemptible context.
> 
> Signed-off-by: Zqiang <qiang1.zhang@...el.com>
> ---
>  mm/util.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/util.c b/mm/util.c
> index 12984e76767e..465f8b8824ca 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -1124,8 +1124,12 @@ void mem_dump_obj(void *object)
>  		return;
>  	}
>  
> -	if (vmalloc_dump_obj(object))
> -		return;
> +	if (is_vmalloc_addr(object)) {
> +		if (preemptible() && vmalloc_dump_obj(object))
>
>preemptible() --> !in_interrupt()?

Hi Leizhen 

!in_interrupt()  not include following scenario:

task context:

local_irq_save() or preempt_disable();
call_rcu()
      mem_dump_obj()
	vmalloc_dump_obj()
		spin_lock(&vmap_area_lock)
local_irq_restore() or preempt_denable();

for PREEMPT-RT kernel, spinlock will convert to sleepable lock.

>
> +			return;
> +		type = "vmalloc memory";
> +		goto end;
> +	}
>
>Move into vmalloc_dump_obj()?

you mean move preemptible() into vmalloc_dump_obj()?

Thanks
Zqiang

>
>  
>  	if (virt_addr_valid(object))
>  		type = "non-slab/vmalloc memory";
> @@ -1135,7 +1139,7 @@ void mem_dump_obj(void *object)
>  		type = "zero-size pointer";
>  	else
>  		type = "non-paged memory";
> -
> +end:
>  	pr_cont(" %s\n", type);
>  }
>  EXPORT_SYMBOL_GPL(mem_dump_obj);
> 

-- 
Regards,
  Zhen Lei