linux-kernel - Re: [PATCH v1] mm/gup: remove (VM_)BUG

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Message-ID: <ef0a22a9-facf-4b3a-ab44-64fb1b06aba0@redhat.com>
Date: Wed, 4 Jun 2025 18:01:18 +0200
From: David Hildenbrand <david@...hat.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 John Hubbard <jhubbard@...dia.com>, Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH v1] mm/gup: remove (VM_)BUG_ONs

On 04.06.25 17:14, Jason Gunthorpe wrote:
> On Wed, Jun 04, 2025 at 04:05:44PM +0200, David Hildenbrand wrote:
>> Especially once we hit one of the assertions in
>> sanity_check_pinned_pages(), observing follow-up assertions failing
>> in other code can give good clues about what went wrong, so use
>> VM_WARN_ON_ONCE instead.
>>
>> While at it, let's just convert all VM_BUG_ON to VM_WARN_ON_ONCE as
>> well. Add one comment for the pfn_valid() check.
>>
>> We have to introduce VM_WARN_ON_ONCE_VMA() to make that fly.
> 
> I'm fine with this, but IMHO, using ON_ONCE is wasteful here.
> 
> They have been BUG_ONs for ages, they really do never happen. If there
> was ever a case to justify not using ON_ONCE this is it..

Well, history told us that if one of them happens, we get a whole flood.

... which is usually not particularly helpful when trying to extract 
information from a syslog :)

DEBUG_VM is already "wasteful" ... ;)

-- 
Cheers,

David / dhildenb