linux-kernel - Re: [PATCH 4/4] mm/vmalloc: remove vfree

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Date:   Thu, 30 Mar 2017 18:27:28 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     <akpm@...ux-foundation.org>, <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>, <tglx@...utronix.de>
Subject: Re: [PATCH 4/4] mm/vmalloc: remove vfree_atomic()

On 03/30/2017 08:18 PM, Matthew Wilcox wrote:
> On Thu, Mar 30, 2017 at 01:27:19PM +0300, Andrey Ryabinin wrote:
>> vfree() can be used in any atomic context and there is no
>> vfree_atomic() callers left, so let's remove it.
> 
> We might still get warnings though.
> 
>> @@ -1588,9 +1556,11 @@ void vfree(const void *addr)
>>  
>>  	if (!addr)
>>  		return;
>> -	if (unlikely(in_interrupt()))
>> -		__vfree_deferred(addr);
>> -	else
>> +	if (unlikely(in_interrupt())) {
>> +		struct vfree_deferred *p = this_cpu_ptr(&vfree_deferred);
>> +		if (llist_add((struct llist_node *)addr, &p->list))
>> +			schedule_work(&p->wq);
>> +	} else
>>  		__vunmap(addr, 1);
>>  }
>>  EXPORT_SYMBOL(vfree);
> 
> If I disable preemption, then call vfree(), in_interrupt() will not be
> true (I've only incremented preempt_count()), then __vunmap() calls
> remove_vm_area() which calls might_sleep(), which will warn.

The first patch removed this might_sleep() .

> So I think this check needs to change from in_interrupt() to in_atomic().
>