From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 8508B1E50B for ; Sun, 29 Dec 2024 13:06:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1735477580; cv=none; b=uAWcgiCtikZPZXkwOPwNtndFPnVvMfm3kbkrn350Uf52fyYG+5NJfIZeTK7FMG0nmJxRKQNIPID/HKeQm3vjV9RMeaVl2eUFPBYBOTTf7rbXhfJ2eyBQBYiX10EZU1XXX5C+qOzTLljEby4h2+MZQbORWvEbKyr2DuqAw/IvSQA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1735477580; c=relaxed/simple; bh=nndwLLlEzkDbJN6Z1dsl++j2uv7DwO7MKRo+94+3crc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Vh+4C2RXMmDZmy6PWOgqjKMoZHSFbsX/R97rcjlMPlwaW0CavyVi2v7yhJOoQOuYbYxLoPZTgKSp8vKLFWrdSaFbAAo/Jbo/dONh2qMbwhE5wcGoKOrpwDgGmSq1b6A9/EqUDbbKvq6eJ/5m4r7fYteJImSv2H8YfVySRDUAfW8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none 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=Ej/tCH5q; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none 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="Ej/tCH5q" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1735477577; 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:references:references; bh=nndwLLlEzkDbJN6Z1dsl++j2uv7DwO7MKRo+94+3crc=; b=Ej/tCH5qs22vG28/hcznVV0sOUxkpZeqaAi9QYbHEJG6as9rW3FyM2wV8Sjg3cPatGKnZ2 GdqnW/t0tq5vcLDSwKviqSRrhOdrr/D2gh/jki+VM8yHmJjZAVN/BF8bWyU4Z4pvAIKaZD Q15aKb99lXCIXuqfCTGQIax6YGJwKPQ= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-441-ZrqYA2dJOi2b6ypdbDHSQw-1; Sun, 29 Dec 2024 08:06:14 -0500 X-MC-Unique: ZrqYA2dJOi2b6ypdbDHSQw-1 X-Mimecast-MFC-AGG-ID: ZrqYA2dJOi2b6ypdbDHSQw Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (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-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5225E195608C; Sun, 29 Dec 2024 13:06:12 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.224.22]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id B76CD19560AA; Sun, 29 Dec 2024 13:06:09 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Sun, 29 Dec 2024 14:05:47 +0100 (CET) Date: Sun, 29 Dec 2024 14:05:43 +0100 From: Oleg Nesterov To: Manfred Spraul Cc: Linus Torvalds , WangYuli , linux-fsdevel , Linux Kernel Mailing List , Christian Brauner Subject: Re: [RESEND PATCH] fs/pipe: Introduce a check to skip sleeping processes during pipe read/write Message-ID: <20241229130543.GC27491@redhat.com> References: <75B06EE0B67747ED+20241225094202.597305-1-wangyuli@uniontech.com> <20241226201158.GB11118@redhat.com> <1df49d97-df0e-4471-9e40-a850b758d981@colorfullife.com> <20241228143248.GB5302@redhat.com> <20241228152229.GC5302@redhat.com> <20241229115741.GB27491@redhat.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 On 12/29, Manfred Spraul wrote: > > >I think that your patch (and the original patch from WangYuli) has the same > >proble with pipe_poll()->poll_wait()->__pollwait(). > > What is the memory barrier for pipe_poll()? > > There is poll_wait()->__pollwait()->add_wait_queue()->spin_unlock(). thus > only store_release. > > And then READ_ONCE(), i.e. no memory barrier. > > Thus the CPU would be free to load pipe->head and pipe->tail before adding > the entry to the poll table. > > Correct? Yes, this was my thinking. See also my initial reply to WangYuli https://lore.kernel.org/all/20241226160007.GA11118@redhat.com/ Do you agree? Oleg.