From mboxrd@z Thu Jan  1 00:00:00 1970
From: Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [RFC PATCH for 4.21 04/16] mm: Introduce vm_map_user_ram,
 vm_unmap_user_ram
Date: Tue, 16 Oct 2018 14:30:16 -0400
Message-ID: <20181016143016.10da89bd@gandalf.local.home>
References: <20181010191936.7495-1-mathieu.desnoyers@efficios.com>
        <20181010191936.7495-5-mathieu.desnoyers@efficios.com>
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To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>, "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>, Boqun Feng <boqun.feng@gmail.com>, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>, Andy Lutomirski <luto@amacapital.net>, Dave Watson <davejwatson@fb.com>, Paul Turner <pjt@google.com>, Andrew Morton <akpm@linux-foundation.org>, Russell King <linux@arm.linux.org.uk>, Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>, Andi Kleen <andi@firstfloor.org>, Chris Lameter <cl@linux.com>, Ben Maurer <bmaurer@fb.com>, Josh Triplett <josh@joshtriplett.org>, Linus Torvalds <torvalds@linux-foundation.org>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Michael Kerrisk <mtk.manpages@g>
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On Wed, 10 Oct 2018 15:19:24 -0400
Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:

> + * vm_unmap_user_ram - unmap linear kernel address space set up by vm_map_user_ram
> + * @mem: the pointer returned by vm_map_user_ram
> + * @count: the count passed to that vm_map_user_ram call (cannot unmap partial)
> + */
> +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:

	if (WARN_ON(x))
		return;

-- Steve