linux-kernel - Re: [RFC PATCH for 4.21 03/16] mm: Replace BUG_ON() by WARN_ON() in vm_unmap

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Date:   Thu, 1 Nov 2018 15:57:53 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     rostedt <rostedt@...dmis.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        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>,
        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@...il.com>,
        Matthew Wilcox <mawilcox@...rosoft.com>
Subject: Re: [RFC PATCH for 4.21 03/16] mm: Replace BUG_ON() by WARN_ON() in
 vm_unmap_ram()

----- On Nov 1, 2018, at 7:46 PM, rostedt rostedt@...dmis.org wrote:

> On Thu, 1 Nov 2018 13:21:12 +0100 (CET)
> Thomas Gleixner <tglx@...utronix.de> wrote:
> 
>> Mathieu,
>> 
>> On Thu, 1 Nov 2018, Mathieu Desnoyers wrote:
>> 
>> > It is encouraged to warn and return rather than use BUG_ON() when
>> > the condition can be recovered from in ways that are more graceful than
>> > halting the whole system.
>> 
>> You're failing to desribe how that graceful recovery works.
>> 
> 
> I think the graceful recovery is to simply return:
> 
>	if (WARN_ON(cond))
>		return;
> 
> is better than just
> 
>	BUG_ON(cond);
> 
> As that's what Linus made pretty clear at the Maintainer's Summit.

That's it. For an unmap function, this basically boils down to
print a warning and leak the memory on internal unmap error.

I will update the commit message describing this behavior.

Thanks,

Mathieu

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