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Tue, 16 Jan 2018 20:32:40 +0000 From: Matan Azrad To: "Ananyev, Konstantin" , 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: AQHTihf/M9xg8LYorUSRFqZtTc27hqNtNdVQgAFomACAAAOCwIAAuwQAgABvY+CABQwJgIAAEk3ggABinoCAANUIAIAAxQGAgAAGCnA= Date: Tue, 16 Jan 2018 20:32:40 +0000 Message-ID: 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> <2601191342CEEE43887BDE71AB9772588627DE30@irsmsx105.ger.corp.intel.com> <2601191342CEEE43887BDE71AB9772588627E954@irsmsx105.ger.corp.intel.com> In-Reply-To: <2601191342CEEE43887BDE71AB9772588627E954@irsmsx105.ger.corp.intel.com> Accept-Language: en-US, he-IL Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: spf=none (sender IP is ) smtp.mailfrom=matan@mellanox.com; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: Mellanox.com X-MS-Exchange-CrossTenant-Network-Message-Id: c18aa24d-992e-4fcf-e2df-08d55d204a27 X-MS-Exchange-CrossTenant-originalarrivaltime: 16 Jan 2018 20:32:40.6789 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: a652971c-7d2e-4d9b-a6a4-d149256f461b X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM6PR0502MB3654 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: Tue, 16 Jan 2018 20:32:42 -0000 Hi Konstantin From: Ananyev, Konstantin, Tuesday, January 16, 2018 9:11 PM > Hi Matan, >=20 > > > > Hi Konstantin > > From: Ananyev, Konstantin, Monday, January 15, 2018 8:44 PM > > > Hi Matan, > > > > Hi Konstantin > > > > 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 PM > > > > > > > > > > > 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 using 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 > > > > > > > > > directly > > > > > > > related. > > > > > > > > > You may create new owner_id but it doesn't mean you > > > > > > > > > would update 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 same 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 > mistake). > > > > - context switch > > > > - allocate new id by thread 1 and get X and change next_id to X+1 > > > atomically. > > > > - 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? > > > > The owner set API validation by thread 0 should fail because the owner > validation is included in the protected section. >=20 > Then your validation function would fail even if you'll use atomic ops in= stead > of lock. No. With atomic this specific scenario will cause the validation to pass. With lock no next_id changes can be done while the thread is in the set API= .=20 > But in fact your code is not protected for that scenario - doesn't matter= will > you'll use lock or atomic ops. > Let's considerer your current code with the following scenario: >=20 > next_owner_id =3D=3D 1 > 1) Process 0: > rte_eth_dev_owner_new(&owner_id); > now owner_id =3D=3D 1 and next_owner_id =3D=3D 2 > 2) Process 1 (by mistake): > rte_eth_dev_owner_set(port_id=3D1, owner->id=3D1); It will complete > successfully, as owner_id =3D=3D1 is considered as valid. > 3) Process 0: > rte_eth_dev_owner_set(port_id=3D1, owner->id=3D1); It will also com= plete > with success, as owner->id is valid is equal to current port owner_id. > So you finished with 2 processes assuming that they do own exclusively th= en > same port. >=20 > Honestly in that situation locking around nest_owner_id wouldn't give yo= u > any advantages over atomic ops. >=20 This is a different scenario that we can't protect on it with atomic or loc= ks. But for the first scenario I described I think we can. Please read it again, I described it step by step. > > > > > I don't think you can protect yourself against such scenario with or > > > without locking. > > > Unless you'll make it harder for the mis-behaving thread to guess > > > valid owner_id, or add some extra logic here. > > > > > > > > > > > > > > > > > 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 not relevant any more. > > > > > > > > > > > > > > > > > > > > > > > > > I agree about the uuid but still think the same lock > > > > > > > > should be used 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 anywa= y. > > > > > > > > > > > > > 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 protected > > > 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 and 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 that you'll have to be really unlucky. > > > > > Though in most cases as you said it would just not operate correc= tly. > > > > > I think if we start to protect dev->name by lock we need to do > > > > > it for all instances (both read and write). > > > > > > > > > Since under the ownership rules, the user must take ownership of a > > > > port > > > before 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. > > > > > So? The user still should take ownership of a device before using it (b= y > name or by port id). > > It can just read it without owning it, but no managing it. > > > > > > Please, Can you describe specific crash scenario and explain how > > > > could the > > > 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. > > Which wrong device do you mean? I guess it is the device which currentl= y is > being created by thread 0. > > > Then rte_pmd_ring_remove() will call rte_free() for related > > > resources, while It can still be in use by someone else. > > The rte_pmd_ring_remove caller(some DPDK entity) must take ownership > > (or validate that he is the owner) of a port before doing it(free, rele= ase), so > no issue here. >=20 > Forget about ownership for a second. > Suppose we have a process it created ring port for itself (without settin= g any > ownership) and used it for some time. > Then it decided to remove it, so it calls rte_pmd_ring_remove() for it. > At the same time second process decides to call rte_eth_dev_allocate() (l= et > say for anither ring port). > They could collide trying to read (process 0) and modify (process 1) same > string rte_eth_dev_data[].name. > Do you mean that process 0 will compare successfully the process 1 new port= name? The state are in local process memory - so process 0 will not compare the p= rocess 1 port, from its point of view this port is in UNUSED state.=20 > Konstantin >=20 > > > > > > Also I'm not sure I fully understand your scenario looks like moving > > the device state setting in allocation to be after the name setting wil= l be > good. > > What do you think? > > > > > Konstantin > > > > > > > > > > > > > Maybe if it had been called just a moment after, It might get > > > > > > different > > > > > answer. > > > > > > Because these APIs don't change ethdev structure(just read), > > > > > > it can be > > > OK. > > > > > > But again, I can understand to use ownership lock also here. > > > > > > > > > > > > > > > > Konstantin