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

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Message-ID: <20250604151432.GC17991@ziepe.ca>
Date: Wed, 4 Jun 2025 12:14:32 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: David Hildenbrand <david@...hat.com>
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 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..

Jason