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dkim=none (message not signed) header.d=none;openvz.org; dmarc=none action=none header.from=virtuozzo.com; Received: from AM7PR08MB5494.eurprd08.prod.outlook.com (2603:10a6:20b:dc::15) by AM6PR08MB4341.eurprd08.prod.outlook.com (2603:10a6:20b:b9::22) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4042.16; Fri, 16 Apr 2021 08:14:34 +0000 Received: from AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b403:c1a9:6bb7:133]) by AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b403:c1a9:6bb7:133%8]) with mapi id 15.20.4042.019; Fri, 16 Apr 2021 08:14:34 +0000 Subject: Re: [PATCH v3 33/33] block/nbd: drop connection_co To: qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, eblake@redhat.com, mreitz@redhat.com, kwolf@redhat.com, rvkagan@yandex-team.ru, den@openvz.org References: <20210416080911.83197-1-vsementsov@virtuozzo.com> <20210416080911.83197-34-vsementsov@virtuozzo.com> From: Vladimir Sementsov-Ogievskiy Message-ID: Date: Fri, 16 Apr 2021 11:14:32 +0300 User-Agent: Mozilla/5.0 (X11; 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envelope-from=vsementsov@virtuozzo.com; helo=EUR03-AM5-obe.outbound.protection.outlook.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 16.04.2021 11:09, Vladimir Sementsov-Ogievskiy wrote: > OK, that's a big rewrite of the logic. > > Pre-patch we have an always running coroutine - connection_co. It does > reply receiving and reconnecting. And it leads to a lot of difficult > and unobvious code around drained sections and context switch. We also > abuse bs->in_flight counter which is increased for connection_co and > temporary decreased in points where we want to allow drained section to > begin. One of these place is in another file: in nbd_read_eof() in > nbd/client.c. > > We also cancel reconnect and requests waiting for reconnect on drained > begin which is not correct. > > Let's finally drop this always running coroutine and go another way: > > 1. reconnect_attempt() goes to nbd_co_send_request and called under > send_mutex > > 2. We do receive headers in request coroutine. But we also should > dispatch replies for another pending requests. So, > nbd_connection_entry() is turned into nbd_receive_replies(), which > does reply dispatching until it receive another request headers, and > returns when it receive the requested header. > > 3. All old staff around drained sections and context switch is dropped. > > Signed-off-by: Vladimir Sementsov-Ogievskiy Please consider this last patch as RFC for now: 1. It is complicated, and doesn't have good documentation. Please look through and ask everything that is not obvious, I'll explain. Don't waste your time trying to understand what is not clean. 2. I also failed to image, how to split the patch into smaller simple patches.. Ideas are welcome. 3. It actually reverts what was done in commit 8c517de24a8a1dcbeb54e7e12b5b0fda42a90ace Author: Vladimir Sementsov-Ogievskiy Date: Thu Sep 3 22:02:58 2020 +0300 block/nbd: fix drain dead-lock because of nbd reconnect-delay and I didn't check yet, does this dead-lock still here or not. Even if it still here I believe that nbd driver is a wrong place to workaround this bug, but I should check it first at least. -- Best regards, Vladimir