linux-kernel - Re: [PATCH 4/7] mm: defer vmalloc from atomic context

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Date:   Mon, 24 Oct 2016 18:44:37 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Christoph Hellwig <hch@....de>, <akpm@...ux-foundation.org>
CC:     <joelaf@...gle.com>, <jszhang@...vell.com>,
        <chris@...is-wilson.co.uk>, <joaodias@...gle.com>,
        <linux-mm@...ck.org>, <linux-rt-users@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/7] mm: defer vmalloc from atomic context



On 10/22/2016 06:17 PM, Christoph Hellwig wrote:
> We want to be able to use a sleeping lock for freeing vmap to keep
> latency down.  For this we need to use the deferred vfree mechanisms
> no only from interrupt, but from any atomic context.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  mm/vmalloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index a4e2cec..bcc1a64 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1509,7 +1509,7 @@ void vfree(const void *addr)
>  
>  	if (!addr)
>  		return;
> -	if (unlikely(in_interrupt())) {
> +	if (unlikely(in_atomic())) {

in_atomic() cannot always detect atomic context, thus it shouldn't be used here.
You can add something like vfree_in_atomic() and use it in atomic call sites.

>  		struct vfree_deferred *p = this_cpu_ptr(&vfree_deferred);
>  		if (llist_add((struct llist_node *)addr, &p->list))
>  			schedule_work(&p->wq);
>