From nobody Wed Feb 11 06:30:17 2026 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 532111E47A5 for ; Wed, 8 Oct 2025 12:32:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759926740; cv=none; b=UQiY1ZSANEJGgO5osP1jY6Gx7MF/1eRCo4J2Zzz+r7rQqFvOje0MPRTiCu1AQwUJn6Y43znezSHQpr096YCDm3cigmznbBT1SanC6NAcV+iAUYLoJMsf7WZT1PLHmUC126EsmcZ/Ms3qiSahTo5yQf61vts1r7c1p2rvGie0z9A= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759926740; c=relaxed/simple; bh=uHqksmuJLKSt+GdkWV/u3ycsK4AeSgh5FUnv2EVyyqY=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; b=VdyiUPjo+L2aLvnxbZGItAd6gnOR8STbG0/N89mEF4OABun1DHlVTKLyanH4683gQBogqrk55/cZ2CCnCQLheW/GDDbnV8LC4+db16w6h+iIhXx4plr6Ga6cPBwztBYEkIixLzx5+OyOPHyfm0xssVSHYHcKxQqEm9SvKDcKexY= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=gm4yheLG; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="gm4yheLG" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1759926737; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to; bh=0Ag5D+pguf9nHfO9uoXExb7dGwEZzjEQQ2eIuAoJM0g=; b=gm4yheLGF0lntM7cqwssxNQxwwDhTK7yfxKwyIhtIctBRgIJA1+BT2PMWf6pGjUAZKYvCg sU/dZjZKuKu9Tgk86zjrsVLpB1klmrjbT5xhpyVsuwstEsMOjqtosavn5I28uvJfbd86xA PnjUwihmrn2K+anyTebo66EgpSYaEps= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-322-RblnqmgiPrym8XO7raAsXQ-1; Wed, 08 Oct 2025 08:32:14 -0400 X-MC-Unique: RblnqmgiPrym8XO7raAsXQ-1 X-Mimecast-MFC-AGG-ID: RblnqmgiPrym8XO7raAsXQ_1759926732 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 4C0111800451; Wed, 8 Oct 2025 12:32:12 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.227.6]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 110961956056; Wed, 8 Oct 2025 12:32:07 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 8 Oct 2025 14:30:51 +0200 (CEST) Date: Wed, 8 Oct 2025 14:30:45 +0200 From: Oleg Nesterov To: Alexander Viro , Boqun Feng , David Howells , Ingo Molnar , Li RongQing , Linus Torvalds , Peter Zijlstra , Waiman Long , Will Deacon Cc: linux-kernel@vger.kernel.org Subject: [PATCH v2 1/4] seqlock: introduce scoped_seqlock_read() and scoped_seqlock_read_irqsave() Message-ID: <20251008123045.GA20440@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20251008123014.GA20413@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 =3D 0; do { seq =3D nextseq; flags =3D read_seqbegin_or_lock_irqsave(&seqlock, &seq); // read-side critical section nextseq =3D 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 } Signed-off-by: Oleg Nesterov Reviewed-by: Oleg Nesterov --- include/linux/seqlock.h | 64 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 64 insertions(+) diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h index 5ce48eab7a2a..fa8d73668f4b 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -1209,4 +1209,68 @@ done_seqretry_irqrestore(seqlock_t *lock, int seq, u= nsigned long flags) if (seq & 1) read_sequnlock_excl_irqrestore(lock, flags); } + +/* internal helper for scoped_seqlock_read/scoped_seqlock_read_irqsave */ +static inline bool +__scoped_seqlock_read_retry(seqlock_t *lock, int *seq, unsigned long *flag= s) +{ + bool retry =3D false; + + if (*seq & 1) { + if (flags) + read_sequnlock_excl_irqrestore(lock, *flags); + else + read_sequnlock_excl(lock); + } else if (read_seqretry(lock, *seq)) { + *seq =3D 1; + retry =3D true; + if (flags) + read_seqlock_excl_irqsave(lock, *flags); + else + read_seqlock_excl(lock); + } + + return retry; +} + +#define __scoped_seqlock_read(lock, s) \ + for (struct { bool lockless; int seq; } \ + s =3D { .lockless =3D true, .seq =3D read_seqbegin(lock) }; \ + s.lockless || __scoped_seqlock_read_retry(lock, &s.seq, NULL); \ + s.lockless =3D false) + +#define __scoped_seqlock_read_irqsave(lock, s) \ + for (struct { bool lockless; int seq; unsigned long flags; } \ + s =3D { .lockless =3D true, .seq =3D read_seqbegin(lock) }; \ + s.lockless || __scoped_seqlock_read_retry(lock, &s.seq, &s.flags); \ + s.lockless =3D false) + +/** + * scoped_seqlock_read(lock) - execute the read side critical section + * without manual sequence counter handling + * or calls to other helpers + * @lock: pointer to the seqlock_t protecting the data + * + * Example: + * + * scoped_seqlock_read(&lock) { + * // read-side critical section + * } + * + * Starts with a lockless pass first. If it fails, restarts the critical + * section with the lock held. + * + * The critical section must not contain control flow that escapes the loo= p. + */ +#define scoped_seqlock_read(lock) \ + __scoped_seqlock_read(lock, __UNIQUE_ID(s)) + +/** + * scoped_seqlock_read_irqsave(lock) - same as scoped_seqlock_read() but + * disables irqs on a locking pass + * @lock: pointer to the seqlock_t protecting the data + */ +#define scoped_seqlock_read_irqsave(lock) \ + __scoped_seqlock_read_irqsave(lock, __UNIQUE_ID(s)) + #endif /* __LINUX_SEQLOCK_H */ --=20 2.25.1.362.g51ebf55