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 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.lore.kernel.org (Postfix) with ESMTPS id 7ED44C83F10 for ; Mon, 28 Aug 2023 01:05:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1693184705; h=from:from:sender:sender: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:list-id:list-help:list-unsubscribe: list-subscribe:list-post; bh=joEHMg4Vnx51INzte3pGka01/tHMgi/viw3PIuubDEg=; b=hSB7vULoRAHqXpGHy8zJ1VBgYvaZCS4A/BRF3GJyPxK2sPAkr2es9ioAmEGx7lXVxEx3/P iDmHwFeNb2+rYSh0Coz+HJw3B20EU2PvGsccSOJYnaZlpDD+U85sxNEDrJp3M5448nA9Gd aXLxXCujwxl72DynbLx4e7Kcb5cPZQ0= Received: from mimecast-mx02.redhat.com (66.187.233.73 [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-115-ZH0jhgXdOrS31JfI2psQBA-1; Sun, 27 Aug 2023 21:04:59 -0400 X-MC-Unique: ZH0jhgXdOrS31JfI2psQBA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C88C529AB3E0; Mon, 28 Aug 2023 01:04:58 +0000 (UTC) Received: from mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com [10.30.29.100]) by smtp.corp.redhat.com (Postfix) with ESMTP id EBF33C15E6A; Mon, 28 Aug 2023 01:04:57 +0000 (UTC) Received: from mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (localhost [IPv6:::1]) by mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (Postfix) with ESMTP id 9CBF619465B3; Mon, 28 Aug 2023 01:04:57 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) by mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (Postfix) with ESMTP id 934F519465A8 for ; Mon, 28 Aug 2023 01:04:56 +0000 (UTC) Received: by smtp.corp.redhat.com (Postfix) id 726A01121319; Mon, 28 Aug 2023 01:04:56 +0000 (UTC) Received: from mimecast-mx02.redhat.com (mimecast09.extmail.prod.ext.rdu2.redhat.com [10.11.55.25]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6AA6D1121318 for ; Mon, 28 Aug 2023 01:04:56 +0000 (UTC) Received: from us-smtp-1.mimecast.com (us-smtp-inbound-delivery-1.mimecast.com [207.211.31.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4E03729AB3E0 for ; Mon, 28 Aug 2023 01:04:56 +0000 (UTC) Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-463-XYU6KTSOONukwlsY-U7oHg-1; Sun, 27 Aug 2023 21:04:53 -0400 X-MC-Unique: XYU6KTSOONukwlsY-U7oHg-1 Received: from viro by zeniv.linux.org.uk with local (Exim 4.96 #2 (Red Hat Linux)) id 1qaQgN-001R4E-2B; Mon, 28 Aug 2023 01:04:43 +0000 Date: Mon, 28 Aug 2023 02:04:43 +0100 From: Al Viro To: Christoph Hellwig Message-ID: <20230828010443.GV3390869@ZenIV> References: <20230601145904.1385409-1-hch@lst.de> <20230601145904.1385409-4-hch@lst.de> <20230827194122.GA325446@ZenIV> MIME-Version: 1.0 In-Reply-To: <20230827194122.GA325446@ZenIV> X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Subject: Re: [Cluster-devel] [PATCH 03/12] filemap: update ki_pos in generic_perform_write X-BeenThere: cluster-devel@redhat.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: "\[Cluster devel\]" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Darrick J. Wong" , linux-mm@kvack.org, Miklos Szeredi , Matthew Wilcox , cluster-devel@redhat.com, Ilya Dryomov , linux-ext4@vger.kernel.org, Chao Yu , linux-nfs@vger.kernel.org, linux-block@vger.kernel.org, Damien Le Moal , Hannes Reinecke , Jaegeuk Kim , ceph-devel@vger.kernel.org, Xiubo Li , Trond Myklebust , Jens Axboe , Christian Brauner , Theodore Ts'o , linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, Anna Schumaker , linux-fsdevel@vger.kernel.org, Andrew Morton Errors-To: cluster-devel-bounces@redhat.com Sender: "Cluster-devel" X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: zeniv.linux.org.uk Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Sun, Aug 27, 2023 at 08:41:22PM +0100, Al Viro wrote: > That part is somewhat fishy - there's a case where you return a positive value > and advance ->ki_pos by more than that amount. I really wonder if all callers > of ->write_iter() are OK with that. Speaking of which, in case of negative return value we'd better *not* use ->ki_pos; consider e.g. generic_file_write_iter() with O_DSYNC and vfs_fsync_range() failure. An error gets returned, but ->ki_pos is left advanced. Normal write(2) is fine - it will only update file->f_pos if ->write_iter() has returned a non-negative. However, io_uring kiocb_done() starts with if (req->flags & REQ_F_CUR_POS) req->file->f_pos = rw->kiocb.ki_pos; if (ret >= 0 && (rw->kiocb.ki_complete == io_complete_rw)) { if (!__io_complete_rw_common(req, ret)) { /* * Safe to call io_end from here as we're inline * from the submission path. */ io_req_io_end(req); io_req_set_res(req, final_ret, io_put_kbuf(req, issue_flags)); return IOU_OK; } } else { io_rw_done(&rw->kiocb, ret); } Note that ->f_pos update is *NOT* conditional upon ret >= 0 - it happens no matter what, provided that original request had ->kiocb.ki_pos equal to -1 (on a non-FMODE_STREAM file). Jens, is there any reason for doing that unconditionally? IMO it's a bad idea - there's a wide scope for fuckups that way, especially since write(2) is not sensitive to that and this use of -1 ki_pos is not particularly encouraged on io_uring side either, AFAICT. Worse, it's handling of failure exits in the first place, which already gets little testing...