linux-kernel - Re: [PATCH v4 03/10] mm/vma: rename is_vma_write

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Message-ID: <df8bec23-4ea1-4f52-995b-cf847ee9a289@suse.cz>
Date: Mon, 26 Jan 2026 11:12:36 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...nel.org>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>, Mike Rapoport
 <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>,
 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 v4 03/10] mm/vma: rename is_vma_write_only(), separate out
 shared refcount put

On 1/23/26 21:12, Lorenzo Stoakes wrote:
> The is_vma_writer_only() function is misnamed - this isn't determining if
> there is only a write lock, as it checks for the presence of the
> VM_REFCNT_EXCLUDE_READERS_FLAG.
> 
> Really, it is checking to see whether readers are excluded, with a
> possibility of a false positive in the case of a detachment (there we
> expect the vma->vm_refcnt to eventually be set to
> VM_REFCNT_EXCLUDE_READERS_FLAG, whereas for an attached VMA we expect it to
> eventually be set to VM_REFCNT_EXCLUDE_READERS_FLAG + 1).
> 
> Rename the function accordingly.
> 
> Relatedly, we use a __refcount_dec_and_test() primitive directly in
> vma_refcount_put(), using the old value to determine what the reference
> count ought to be after the operation is complete (ignoring racing
> reference count adjustments).
> 
> Wrap this into a __vma_refcount_put_return() function, which we can then
> utilise in vma_mark_detached() and thus keep the refcount primitive usage
> abstracted.
> 
> This function, as the name implies, returns the value after the reference
> count has been updated.
> 
> This reduces duplication in the two invocations of this function.
> 
> Also adjust comments, removing duplicative comments covered elsewhere and
> adding more to aid understanding.
> 
> No functional change intended.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>