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=-10.7 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable 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 4D260C31E45 for ; Thu, 13 Jun 2019 16:23:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 26A492147A for ; Thu, 13 Jun 2019 16:23:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1560443027; bh=JUTwg6JYVMcanXtm5O5FyNtXQi+NRAjPJmKWbUZPEa0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=F0cFy2k1EDlBj1PryyTFR16edcZxTlMVbTI5ybJlD7RKFeFKV6l5DiwL0AhW7ddKf T+Ie473gBNQFhtq0Ir0PND5QRlMJ8QbQdU0UhKKPKoY4Cf2BAL5ytuG3NIwQYWYCOD CMYm2FfGV99k4Sd3tBy/c5IGDryBjGv5W/D+yazU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391235AbfFMQXp (ORCPT ); Thu, 13 Jun 2019 12:23:45 -0400 Received: from mail.kernel.org ([198.145.29.99]:54974 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731011AbfFMIhg (ORCPT ); Thu, 13 Jun 2019 04:37:36 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3E9CC2064A; Thu, 13 Jun 2019 08:37:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1560415054; bh=JUTwg6JYVMcanXtm5O5FyNtXQi+NRAjPJmKWbUZPEa0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=WAqL5yGaOPZp4ECIXPbiO/qhy9EPBa/9JGPqjeA1H5k03KyXpy0b7g2T3kMyVnkcO w5fpOjowoJnuvEomB0nPBurAEBxcYvr0OPzhxqmc/iM+XD2GPowSyDBhgWCcFVYAOO eAQFwq9POwPglB70uRjIggZaJINUGB74Lv/tPvCs= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Kirill Smelkov , Han-Wen Nienhuys , Jakob Unterwurzacher , Miklos Szeredi , Sasha Levin Subject: [PATCH 4.14 43/81] fuse: retrieve: cap requested size to negotiated max_write Date: Thu, 13 Jun 2019 10:33:26 +0200 Message-Id: <20190613075652.485457686@linuxfoundation.org> X-Mailer: git-send-email 2.22.0 In-Reply-To: <20190613075649.074682929@linuxfoundation.org> References: <20190613075649.074682929@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [ Upstream commit 7640682e67b33cab8628729afec8ca92b851394f ] FUSE filesystem server and kernel client negotiate during initialization phase, what should be the maximum write size the client will ever issue. Correspondingly the filesystem server then queues sys_read calls to read requests with buffer capacity large enough to carry request header + that max_write bytes. A filesystem server is free to set its max_write in anywhere in the range between [1*page, fc->max_pages*page]. In particular go-fuse[2] sets max_write by default as 64K, wheres default fc->max_pages corresponds to 128K. Libfuse also allows users to configure max_write, but by default presets it to possible maximum. If max_write is < fc->max_pages*page, and in NOTIFY_RETRIEVE handler we allow to retrieve more than max_write bytes, corresponding prepared NOTIFY_REPLY will be thrown away by fuse_dev_do_read, because the filesystem server, in full correspondence with server/client contract, will be only queuing sys_read with ~max_write buffer capacity, and fuse_dev_do_read throws away requests that cannot fit into server request buffer. In turn the filesystem server could get stuck waiting indefinitely for NOTIFY_REPLY since NOTIFY_RETRIEVE handler returned OK which is understood by clients as that NOTIFY_REPLY was queued and will be sent back. Cap requested size to negotiate max_write to avoid the problem. This aligns with the way NOTIFY_RETRIEVE handler works, which already unconditionally caps requested retrieve size to fuse_conn->max_pages. This way it should not hurt NOTIFY_RETRIEVE semantic if we return less data than was originally requested. Please see [1] for context where the problem of stuck filesystem was hit for real, how the situation was traced and for more involving patch that did not make it into the tree. [1] https://marc.info/?l=linux-fsdevel&m=155057023600853&w=2 [2] https://github.com/hanwen/go-fuse Signed-off-by: Kirill Smelkov Cc: Han-Wen Nienhuys Cc: Jakob Unterwurzacher Signed-off-by: Miklos Szeredi Signed-off-by: Sasha Levin --- fs/fuse/dev.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -1678,7 +1678,7 @@ static int fuse_retrieve(struct fuse_con offset = outarg->offset & ~PAGE_MASK; file_size = i_size_read(inode); - num = outarg->size; + num = min(outarg->size, fc->max_write); if (outarg->offset > file_size) num = 0; else if (outarg->offset + num > file_size)