linux-kernel - Re: [PATCH v2 1/3] seqlock: add raw_seqcount_try

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Message-ID: <20241122111914.GS24774@noisy.programming.kicks-ass.net>
Date: Fri, 22 Nov 2024 12:19:14 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: David Hildenbrand <david@...hat.com>
Cc: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org,
	andrii@...nel.org, jannh@...gle.com, Liam.Howlett@...cle.com,
	lorenzo.stoakes@...cle.com, vbabka@...e.cz, mhocko@...nel.org,
	shakeel.butt@...ux.dev, hannes@...xchg.org, willy@...radead.org,
	brauner@...nel.org, oleg@...hat.com, arnd@...db.de,
	richard.weiyang@...il.com, zhangpeng.00@...edance.com,
	linmiaohe@...wei.com, viro@...iv.linux.org.uk, hca@...ux.ibm.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] seqlock: add raw_seqcount_try_begin

On Fri, Nov 22, 2024 at 12:10:29PM +0100, David Hildenbrand wrote:

> In gup_fast(), we simply do
> 
> seq = raw_read_seqcount(&current->mm->write_protect_seq);
> if (seq & 1)
> 	return 0;
> 
> Should we be using that there as well?
> 
> if (!raw_seqcount_try_begin(&current->mm->write_protect_seqs, seq))
> 	return 0;

Might as well. A quick grep doesn't find me another instance of this
pattern, but does find me something 'funny' in net/netfilter/x_tables.c.
Let's pretend I didn't see that for now ... *sigh*

Want me to stick a patch like this on, or do you want to do that later,
when the dust has settled?