linux-kernel - Re: [patch] mm, debug: allow suppressing panic on CONFIG_DEBUG

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Message-ID: <703a3995-75cf-b575-deff-fe2b78bd1354@google.com>
Date:   Tue, 23 May 2023 17:54:43 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Matthew Wilcox <willy@...radead.org>
cc:     David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>, Alex Shi <alexs@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Alexander Duyck <alexanderduyck@...com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch] mm, debug: allow suppressing panic on CONFIG_DEBUG_VM
 checks

On Tue, 23 May 2023, Matthew Wilcox wrote:

> On Mon, May 22, 2023 at 11:39:27AM -0700, David Rientjes wrote:
> > I think VM_BUG_ON*() and friends are used to crash the kernel for 
> > debugging so that we get a crash dump and because some variants don't 
> > exist for VM_WARN_ON().  There's no VM_WARN_ON_PAGE(), for example, unless 
> > implicitly converted with this patch.
> 
> It could be added, but there's already a VM_WARN_ON_FOLIO() and
> VM_WARN_ON_ONCE_PAGE(), so hopefully we just keep converting code
> to folios until nobody notices that we might need such a thing.
> 

Yeah, the lack of VM_WARN variants for VM_BUG_ON_MM or VM_BUG_ON_VMA are 
probably better examples.  But it looks like we're converging toward 
eliminating VM_BUG_ON* variants entirely and relying on 
kernel.panic_on_warn to do the BUG_ON() behavior if we want to opt into 
that.  So this will be a useful cleanup.