linux-kernel - Re: [RFC PATCH for 4.21 04/16] mm: Introduce vm_map_user_ram, vm_unmap_user

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Date:   Wed, 17 Oct 2018 11:04:01 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>, Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
        Chris Lameter <cl@...ux.com>, Ben Maurer <bmaurer@...com>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Joel Fernandes <joelaf@...gle.com>
Subject: Re: [RFC PATCH for 4.21 04/16] mm: Introduce vm_map_user_ram,
 vm_unmap_user_ram

----- On Oct 17, 2018, at 11:00 AM, Mathieu Desnoyers mathieu.desnoyers@...icios.com wrote:

> ----- On Oct 16, 2018, at 8:27 PM, Sergey Senozhatsky
> sergey.senozhatsky.work@...il.com wrote:
> 
>> On (10/16/18 14:30), Steven Rostedt wrote:
>>> > +void vm_unmap_user_ram(const void *mem, unsigned int count)
>>> > +{
>>> > +	unsigned long size = (unsigned long)count << PAGE_SHIFT;
>>> > +	unsigned long addr = (unsigned long)mem;
>>> > +	struct vmap_area *va;
>>> > +
>>> > +	might_sleep();
>>> > +	BUG_ON(!addr);
>>> > +	BUG_ON(addr < VMALLOC_START);
>>> > +	BUG_ON(addr > VMALLOC_END);
>>> > +	BUG_ON(!PAGE_ALIGNED(addr));
>>> > +
>>> > +	debug_check_no_locks_freed(mem, size);
>>> > +	va = find_vmap_area(addr);
>>> > +	BUG_ON(!va);
>>> > +	free_unmap_vmap_area(va);
>>> > +}
>>> > +EXPORT_SYMBOL(vm_unmap_user_ram);
>>> > +
>>> 
>>> Noticing this from Sergey's question in another patch, why are you
>>> using BUG_ON()? That's rather extreme and something we are trying to
>>> avoid adding more of (I still need to remove the BUG_ON()s I've added
>>> over ten years ago). I don't see why all these BUG_ON's can't be turned
>>> into:
>> 
>> +1
>> 
>>> 	if (WARN_ON(x))
>>> 		return;
>> 
>> Given that this somewhat MM-related, I'd may be say VM_WARN_ON().

I notice that VM_WARN_ON() casts the result of WARN_ON() to (void), so it
cannot be used in a if () statement.

VM_WARN_ON() will only warn if CONFIG_DEBUG_VM is set.

Is it really what we want ?

Thanks,

Mathieu


> 
> Good point, will do!
> 
> So I'll do one cleanup patch for vm_unmap_ram(), and I'll modify the new
> vm_unmap_user_ram().
> 
> Thanks,
> 
> Mathieu
> 
>> 
>> 	-ss
> 
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com