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 B6F2C45C18 for ; Sun, 29 Dec 2024 13:14:11 +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=1735478053; cv=none; b=coH0uqmlmVWD1bOrXE2vaJCnmoK2c4mEjDBO6JcBpspRjMK1dbh+rugPdRoz+6cVu/YH4YQgsdS+akxs5BhiAh1n1bb0qIUuI2GJopN0Bf0Djs7SZspyOcjPHs88rFjJfu1igDelaPAVlrEOMbU9eRIv4xq78nSQen5DPaKVNsU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1735478053; c=relaxed/simple; bh=aPyufRnwNBHqezWtme7xCZ714gWP3VpT/ks8zqr4Td0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=uM45NExwIuAVdy4EUgBTm1OmvLNNqBv3Tmko54MqRmxKYoiX6vsuokwXmRn1w+ixroQQk7dNP04XBz8p0D3u5U/YDDdKC5OWpkJQX6jfK9TSKLziuaBx15Fuib7Nc1fOvfm368gXGWg/Dv21JTmL4aJoiPJufFPlyYiFXKzZSM0= 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=bB78sjHD; 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="bB78sjHD" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1735478050; 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=aPyufRnwNBHqezWtme7xCZ714gWP3VpT/ks8zqr4Td0=; b=bB78sjHDJPBByI2nPZhVXveL8QefCds4NGLI279SRgWOSIvMiu/1nOf3TAPZwuOSH1W0MY BYp9fhB4L9yTVZpIzgtHvQDcri5uXKDv2eQF91zn1oXe0mNXqtPQ3NKiw8pkOHj5/IG6HX w5cNXbWKHAPTDX1dfgjcAoOvyj92Pkc= Received: from mx-prod-mc-04.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-303-TBCig1XZOqWSL0oeoNRntA-1; Sun, 29 Dec 2024 08:14:08 -0500 X-MC-Unique: TBCig1XZOqWSL0oeoNRntA-1 X-Mimecast-MFC-AGG-ID: TBCig1XZOqWSL0oeoNRntA 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-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 1090919560A2; Sun, 29 Dec 2024 13:14:07 +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 5C22519560AA; Sun, 29 Dec 2024 13:14:04 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Sun, 29 Dec 2024 14:13:42 +0100 (CET) Date: Sun, 29 Dec 2024 14:13:38 +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: <20241229131338.GD27491@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> <20241229130543.GC27491@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: <20241229130543.GC27491@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 Sorry for the noise... and currently this is fine. But if we want to add the wq_has_sleeper() checks into fs/pipe.c then pipe_poll() needs smp_mb() after it calls poll_wait(). Agreed? On 12/29, Oleg Nesterov wrote: > > 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.