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 09:27:22 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        linux-kernel@...r.kernel.org, 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>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [RFC PATCH for 4.21 04/16] mm: Introduce vm_map_user_ram,
 vm_unmap_user_ram

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().

	-ss