linux-kernel - Re: [PATCH 1/4] mm/vmalloc: allow to call vfree() in atomic context

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Date:   Wed, 5 Apr 2017 13:42:19 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        akpm@...ux-foundation.org
Cc:     penguin-kernel@...ove.SAKURA.ne.jp, linux-kernel@...r.kernel.org,
        mhocko@...nel.org, linux-mm@...ck.org, hpa@...or.com,
        chris@...is-wilson.co.uk, hch@....de, mingo@...e.hu,
        jszhang@...vell.com, joelaf@...gle.com, joaodias@...gle.com,
        willy@...radead.org, tglx@...utronix.de, stable@...r.kernel.org
Subject: Re: [PATCH 1/4] mm/vmalloc: allow to call vfree() in atomic context

On 03/30/2017 04:48 PM, Andrey Ryabinin wrote:
> On 03/30/2017 03:00 PM, Thomas Hellstrom wrote:
> 
>>>  
>>>  	if (unlikely(nr_lazy > lazy_max_pages()))
>>> -		try_purge_vmap_area_lazy();
>>
>> Perhaps a slight optimization would be to schedule work iff
>> !mutex_locked(&vmap_purge_lock) below?
>>
> 
> Makes sense, we don't need to spawn workers if we already purging.
> 
> 
> 
> From: Andrey Ryabinin <aryabinin@...tuozzo.com>
> Subject: mm/vmalloc: allow to call vfree() in atomic context fix
> 
> Don't spawn worker if we already purging.
> 
> Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
> ---
>  mm/vmalloc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index ea1b4ab..88168b8 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -737,7 +737,8 @@ static void free_vmap_area_noflush(struct vmap_area *va)
>  	/* After this point, we may free va at any time */
>  	llist_add(&va->purge_list, &vmap_purge_list);
>  
> -	if (unlikely(nr_lazy > lazy_max_pages()))
> +	if (unlikely(nr_lazy > lazy_max_pages()) &&
> +	    !mutex_is_locked(&vmap_purge_lock))

So, isn't this racy? (and do we care?)

Vlastimil

>  		schedule_work(&purge_vmap_work);
>  }
>  
>