linux-kernel - Re: [PATCH RESEND v3 04/10] mm/vma: add+use vma lockdep acquire/release defines

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Message-ID: <4b0b5a72-d4a0-4e40-8632-d2f9268e9e09@suse.cz>
Date: Fri, 23 Jan 2026 09:41:24 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...nel.org>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>, Mike Rapoport
 <rppt@...nel.org>, Michal Hocko <mhocko@...e.com>,
 Shakeel Butt <shakeel.butt@...ux.dev>, Jann Horn <jannh@...gle.com>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 linux-rt-devel@...ts.linux.dev, Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
 Boqun Feng <boqun.feng@...il.com>, Waiman Long <longman@...hat.com>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Clark Williams <clrkwllms@...nel.org>, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH RESEND v3 04/10] mm/vma: add+use vma lockdep
 acquire/release defines

On 1/22/26 20:41, Suren Baghdasaryan wrote:
>> > +/*
>> > + * VMA locks do not behave like most ordinary locks found in the kernel, so we
>> > + * cannot quite have full lockdep tracking in the way we would ideally prefer.
>> > + *
>> > + * Read locks act as shared locks which exclude an exclusive lock being
>> > + * taken. We therefore mark these accordingly on read lock acquire/release.
>> > + *
>> > + * Write locks are acquired exclusively per-VMA, but released in a shared
>> > + * fashion, that is upon vma_end_write_all(), we update the mmap's seqcount such
>> > + * that write lock is de-acquired.
>> > + *
>> > + * We therefore cannot track write locks per-VMA, nor do we try. Mitigating this
>> > + * is the fact that, of course, we do lockdep-track the mmap lock rwsem.
>> > + *
>> > + * We do, however, want to indicate that during either acquisition of a VMA
>> > + * write lock or detachment of a VMA that we require the lock held be exclusive,
>> > + * so we utilise lockdep to do so.
>> > + */
>> > +#define __vma_lockdep_acquire_read(vma) \
> 
> One question I forgot to ask. Are you adding "__" prefix to indicate
> no other users should be using them or for some other reason?

I'd say it's the case of 'it has to be in a "public" header but not expected
to be used directly" by the end-users of the header'.