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Date: Wed, 8 Oct 2025 14:55:08 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	Boqun Feng <boqun.feng@gmail.com>,
	David Howells <dhowells@redhat.com>, Ingo Molnar <mingo@redhat.com>,
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	Linus Torvalds <torvalds@linux-foundation.org>,
	Waiman Long <longman@redhat.com>, Will Deacon <will@kernel.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/4] seqlock: introduce scoped_seqlock_read() and
 scoped_seqlock_read_irqsave()
Message-ID: <20251008125508.GJ3289052@noisy.programming.kicks-ass.net>
References: <20251008123014.GA20413@redhat.com>
 <20251008123045.GA20440@redhat.com>
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In-Reply-To: <20251008123045.GA20440@redhat.com>

On Wed, Oct 08, 2025 at 02:30:45PM +0200, Oleg Nesterov wrote:
> The read_seqbegin/need_seqretry/done_seqretry API is cumbersome and
> error prone. With the new helper the "typical" code like
> 
> 	int seq, nextseq;
> 	unsigned long flags;
> 
> 	nextseq = 0;
> 	do {
> 		seq = nextseq;
> 		flags = read_seqbegin_or_lock_irqsave(&seqlock, &seq);
> 
> 		// read-side critical section
> 
> 		nextseq = 1;
> 	} while (need_seqretry(&seqlock, seq));
> 	done_seqretry_irqrestore(&seqlock, seq, flags);
> 
> can be rewritten as
> 
> 	scoped_seqlock_read_irqsave (&seqlock) {
> 		// read-side critical section
> 	}
> 

Hmm, on first reading I was expecting that to be:

	do {
		seq = read_seqbegin(&seqlock);

		// read-side section

	} while (read_seqretry(&seqlock, seq));

for lack of that _or_lock() wording, but I suppose we can make that
something like:

 	scoped_seqbegin_read (&seqlock) {
		// read-side section
	}

which is distinctive enough.