From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AED44C43334 for ; Mon, 3 Sep 2018 12:28:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5AE9520862 for ; Mon, 3 Sep 2018 12:28:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5AE9520862 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727784AbeICQsG (ORCPT ); Mon, 3 Sep 2018 12:48:06 -0400 Received: from mx2.suse.de ([195.135.220.15]:56790 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727186AbeICQsF (ORCPT ); Mon, 3 Sep 2018 12:48:05 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 73C80AFE7; Mon, 3 Sep 2018 12:28:08 +0000 (UTC) Date: Mon, 3 Sep 2018 14:28:04 +0200 From: Michal Hocko To: Douglas Gilbert Cc: Richard Weinberger , drorl@infinidat.com, LKML , linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, Linus Torvalds , Christoph Hellwig , Jens Axboe Subject: Re: Recent removal of bsg read/write support Message-ID: <20180903122804.GA15074@dhcp22.suse.cz> References: <6b907fed-d83f-de75-bde4-11270a0b1b0b@interlog.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6b907fed-d83f-de75-bde4-11270a0b1b0b@interlog.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun 02-09-18 21:16:10, Douglas Gilbert wrote: > On 2018-09-02 01:44 PM, Richard Weinberger wrote: > > CC'ing relevant people. Otherwise your mail might get lost. > > > > On Sun, Sep 2, 2018 at 1:37 PM Dror Levin wrote: > > > > > > Note: I am not subscribed to LKML so please CC replies to this email. > > > > > > Hi, > > > > > > We have an internal tool that uses the bsg read/write interface to > > > issue SCSI commands as part of a test suite for a storage device. > > > > > > After recently reading on LWN that this interface is to be removed we > > > tried porting our code to use sg instead. However, that raises new > > > issues - mainly getting ENOMEM over iSCSI for unknown reasons. > > > > > > Because of this we would like to continue using the bsg interface, > > > even if some changes are required to meet security concerns. > > > > > > Is there any chance for this removal to be reverted? I saw it was > > > already included in 4.19-rc1. > > Hi, > Both bsg and sg are relatively thin shims over the same block layer > pass-through calls. And neither driver will themselves generate ENOMEM > unless the CPU is running low of memory. > > In my experience, the main reason for unexpected ENOMEMs *** is from > blk_rq_map_user_iov() in block/blk_map.c called from both drivers. > That is a particular resource shortage rather than memory in general. > I do notice the blk_rq_map_user_iov() is/was called with GFP_KERNEL > in bsg and GFP_ATOMIC by sg. That suggests when you call write() on > a sg device and get ENOMEM, then wait a little (depends on your app) > and try again. Well, what is the reason to use GFP_ATOMIC in the first place? I am not familiar with the code so I might be easily wrong but sg_start_req which calls blk_rq_map_user_iov resp. blk_rq_map_user with GFP_ATOMIC uses mutex. It is a conditional usage so the sleeping context might depend on the caller. But I guess it would be better to double check. It looks suspicious to me. -- Michal Hocko SUSE Labs