From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by dpdk.org (Postfix) with ESMTP id BF24137B4 for ; Mon, 15 Jan 2018 19:43:34 +0100 (CET) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 15 Jan 2018 10:43:33 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.46,364,1511856000"; d="scan'208";a="10380613" Received: from irsmsx102.ger.corp.intel.com ([163.33.3.155]) by fmsmga007.fm.intel.com with ESMTP; 15 Jan 2018 10:43:32 -0800 Received: from irsmsx105.ger.corp.intel.com ([169.254.7.236]) by IRSMSX102.ger.corp.intel.com ([169.254.2.180]) with mapi id 14.03.0319.002; Mon, 15 Jan 2018 18:43:32 +0000 From: "Ananyev, Konstantin" To: Matan Azrad , Thomas Monjalon , Gaetan Rivet , "Wu, Jingjing" CC: "dev@dpdk.org" , Neil Horman , "Richardson, Bruce" Thread-Topic: [PATCH v2 2/6] ethdev: add port ownership Thread-Index: AQHTh5xreoY7ZC2VXUKPLFrmK4AmzKNtEwCwgABGVwCAATRvEIAAOkGAgACPrvCAAIW5gIAE/GJggAAbIoCAAD5+YA== Date: Mon, 15 Jan 2018 18:43:31 +0000 Message-ID: <2601191342CEEE43887BDE71AB9772588627DE30@irsmsx105.ger.corp.intel.com> References: <1511870281-15282-1-git-send-email-matan@mellanox.com> <1515318351-4756-1-git-send-email-matan@mellanox.com> <1515318351-4756-3-git-send-email-matan@mellanox.com> <2601191342CEEE43887BDE71AB97725880E3B9D6@irsmsx105.ger.corp.intel.com> <2601191342CEEE43887BDE71AB9772588627B12A@irsmsx105.ger.corp.intel.com> <2601191342CEEE43887BDE71AB9772588627CCB0@irsmsx105.ger.corp.intel.com> <2601191342CEEE43887BDE71AB9772588627DC25@irsmsx105.ger.corp.intel.com> In-Reply-To: Accept-Language: en-IE, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-titus-metadata-40: eyJDYXRlZ29yeUxhYmVscyI6IiIsIk1ldGFkYXRhIjp7Im5zIjoiaHR0cDpcL1wvd3d3LnRpdHVzLmNvbVwvbnNcL0ludGVsMyIsImlkIjoiZTc0YjY2ZGEtMzNiYS00YWY1LWIzMjktYmI4OTE0YjlhZThhIiwicHJvcHMiOlt7Im4iOiJDVFBDbGFzc2lmaWNhdGlvbiIsInZhbHMiOlt7InZhbHVlIjoiQ1RQX05UIn1dfV19LCJTdWJqZWN0TGFiZWxzIjpbXSwiVE1DVmVyc2lvbiI6IjE2LjUuOS4zIiwiVHJ1c3RlZExhYmVsSGFzaCI6IktOQWFzV2xzSXJWOVRTUFIxRHYxcE1NQnhsdmdHT1pNZzY2aVRUUlF5R1k9In0= x-ctpclassification: CTP_NT dlp-product: dlpe-windows dlp-version: 11.0.0.116 dlp-reaction: no-action x-originating-ip: [163.33.239.182] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Subject: Re: [dpdk-dev] [PATCH v2 2/6] ethdev: add port ownership X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 15 Jan 2018 18:43:35 -0000 Hi Matan, >=20 > Hi Konstantin >=20 > From: Ananyev, Konstantin, Monday, January 15, 2018 1:45 PM > > Hi Matan, > > > > > > > > > > > Hi Konstantin > > > > > > From: Ananyev, Konstantin, Friday, January 12, 2018 2:02 AM > > > > Hi Matan, > > > > > > > > > > > > > > Hi Konstantin > > > > > > > > > > From: Ananyev, Konstantin, Thursday, January 11, 2018 2:40 PM > > > > > > Hi Matan, > > > > > > > > > > > > > > > > > > > > Hi Konstantin > > > > > > > > > > > > > > From: Ananyev, Konstantin, Wednesday, January 10, 2018 3:36 P= M > > > > > > > > Hi Matan, > > > > > > > > > It is good to see that now scanning/updating > > > > > > > > rte_eth_dev_data[] is lock protected, but it might be not > > > > > > > > very plausible to protect both data[] and next_owner_id usi= ng the > > same lock. > > > > > > > > > > > > > > I guess you mean to the owner structure in > > rte_eth_dev_data[port_id]. > > > > > > > The next_owner_id is read by ownership APIs(for owner > > > > > > > validation), so it > > > > > > makes sense to use the same lock. > > > > > > > Actually, why not? > > > > > > > > > > > > Well to me next_owner_id and rte_eth_dev_data[] are not directl= y > > > > related. > > > > > > You may create new owner_id but it doesn't mean you would updat= e > > > > > > rte_eth_dev_data[] immediately. > > > > > > And visa-versa - you might just want to update > > > > > > rte_eth_dev_data[].name or .owner_id. > > > > > > It is not very good coding practice to use same lock for > > > > > > non-related data structures. > > > > > > > > > > > I see the relation like next: > > > > > Since the ownership mechanism synchronization is in ethdev > > > > > responsibility, we must protect against user mistakes as much as > > > > > we can by > > > > using the same lock. > > > > > So, if user try to set by invalid owner (exactly the ID which > > > > > currently is > > > > allocated) we can protect on it. > > > > > > > > Hmm, not sure why you can't do same checking with different lock or > > > > atomic variable? > > > > > > > The set ownership API is protected by ownership lock and checks the > > > owner ID validity By reading the next owner ID. > > > So, the owner ID allocation and set API should use the same atomic > > mechanism. > > > > Sure but all you are doing for checking validity, is check that owner_= id > 0 > > &&& owner_id < next_ownwe_id, right? > > As you don't allow owner_id overlap (16/3248 bits) you can safely do sa= me > > check with just atomic_get(&next_owner_id). > > > It will not protect it, scenario: > - current next_id is X. > - call set ownership of port A with owner id X by thread 0(by user mistak= e). > - context switch > - allocate new id by thread 1 and get X and change next_id to X+1 atomica= lly. > - context switch > - Thread 0 validate X by atomic_read and succeed to take ownership. > - The system loosed the port(or will be managed by two entities) - crash. Ok, and how using lock will protect you with such scenario? I don't think you can protect yourself against such scenario with or withou= t locking. Unless you'll make it harder for the mis-behaving thread to guess valid own= er_id, or add some extra logic here. >=20 >=20 > > > The set(and others) ownership APIs already uses the ownership lock so= I > > think it makes sense to use the same lock also in ID allocation. > > > > > > > > > > > In fact, for next_owner_id, you don't need a lock - just > > > > > > > > rte_atomic_t should be enough. > > > > > > > > > > > > > > I don't think so, it is problematic in next_owner_id > > > > > > > wraparound and may > > > > > > complicate the code in other places which read it. > > > > > > > > > > > > IMO it is not that complicated, something like that should work= I think. > > > > > > > > > > > > /* init to 0 at startup*/ > > > > > > rte_atomic32_t *owner_id; > > > > > > > > > > > > int new_owner_id(void) > > > > > > { > > > > > > int32_t x; > > > > > > x =3D rte_atomic32_add_return(&owner_id, 1); > > > > > > if (x > UINT16_MAX) { > > > > > > rte_atomic32_dec(&owner_id); > > > > > > return -EOVERWLOW; > > > > > > } else > > > > > > return x; > > > > > > } > > > > > > > > > > > > > > > > > > > Why not just to keep it simple and using the same lock? > > > > > > > > > > > > Lock is also fine, I just think it better be a separate one - > > > > > > that would protext just next_owner_id. > > > > > > Though if you are going to use uuid here - all that probably no= t > > > > > > relevant any more. > > > > > > > > > > > > > > > > I agree about the uuid but still think the same lock should be us= ed for > > both. > > > > > > > > But with uuid you don't need next_owner_id at all, right? > > > > So lock will only be used for rte_eth_dev_data[] fields anyway. > > > > > > > Sorry, I meant uint64_t, not uuid. > > > > Ah ok, my thought uuid_t is better as with it you don't need to support= your > > own code to allocate new owner_id, but rely on system libs instead. > > But wouldn't insist here. > > > > > > > > > > > > > Another alternative would be to use 2 locks - one for > > > > > > > > next_owner_id second for actual data[] protection. > > > > > > > > > > > > > > > > Another thing - you'll probably need to grab/release a lock > > > > > > > > inside > > > > > > > > rte_eth_dev_allocated() too. > > > > > > > > It is a public function used by drivers, so need to be prot= ected too. > > > > > > > > > > > > > > > > > > > > > > Yes, I thought about it, but decided not to use lock in next: > > > > > > > rte_eth_dev_allocated > > > > > > > rte_eth_dev_count > > > > > > > rte_eth_dev_get_name_by_port > > > > > > > rte_eth_dev_get_port_by_name > > > > > > > maybe more... > > > > > > > > > > > > As I can see in patch #3 you protect by lock access to > > > > > > rte_eth_dev_data[].name (which seems like a good thing). > > > > > > So I think any other public function that access > > > > > > rte_eth_dev_data[].name should be protected by the same lock. > > > > > > > > > > > > > > > > I don't think so, I can understand to use the ownership lock > > > > > here(as in port > > > > creation) but I don't think it is necessary too. > > > > > What are we exactly protecting here? > > > > > Don't you think it is just timing?(ask in the next moment and you > > > > > may get another answer) I don't see optional crash. > > > > > > > > Not sure what you mean here by timing... > > > > As I understand rte_eth_dev_data[].name unique identifies device an= d > > > > is used by port allocation/release/find functions. > > > > As you stated above: > > > > "1. The port allocation and port release synchronization will be > > > > managed by ethdev." > > > > To me it means that ethdev layer has to make sure that all accesses > > > > to rte_eth_dev_data[].name are atomic. > > > > Otherwise what would prevent the situation when one process does > > > > rte_eth_dev_allocate()->snprintf(rte_eth_dev_data[x].name, ...) > > > > while second one does > > rte_eth_dev_allocated(rte_eth_dev_data[x].name, ...) ? > > > > > > > The second will get True or False and that is it. > > > > Under race condition - in the worst case it might crash, though for tha= t you'll > > have to be really unlucky. > > Though in most cases as you said it would just not operate correctly. > > I think if we start to protect dev->name by lock we need to do it for a= ll > > instances (both read and write). > > > Since under the ownership rules, the user must take ownership of a port b= efore using it, I still don't see a problem here. I am not talking about owner id or name here. I am talking about dev->name. > Please, Can you describe specific crash scenario and explain how could th= e locking fix it? Let say thread 0 doing rte_eth_dev_allocate()->snprintf(rte_eth_dev_data[x]= .name, ...), thread 1 doing rte_pmd_ring_remove()->rte_eth_dev_allocated()->strcmp(). And because of race condition - rte_eth_dev_allocated() will return rte_eth= _dev * for the wrong device. Then rte_pmd_ring_remove() will call rte_free() for related resources, whil= e It can still be in use by someone else. Konstantin >=20 > > > Maybe if it had been called just a moment after, It might get differe= nt > > answer. > > > Because these APIs don't change ethdev structure(just read), it can b= e OK. > > > But again, I can understand to use ownership lock also here. > > > > > > > Konstantin