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Thu, 18 Jan 2018 14:26:18 +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+CABQwJgIAAEk3ggABinoCAANUIAIAAxQGAgAAGCnCAAQnKAIAAAmNwgAAXCYCAAABqkIAAQhEAgAASagCAACqV0IABKccAgAABeuA= Date: Thu, 18 Jan 2018 14:26:18 +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> <2601191342CEEE43887BDE71AB9772588627EE60@irsmsx105.ger.corp.intel.com> <2601191342CEEE43887BDE71AB9772588627EEDA@irsmsx105.ger.corp.intel.com> <2601191342CEEE43887BDE71AB9772588627F076@irsmsx105.ger.corp.intel.com> <2601191342CEEE43887BDE71AB9772588628029A@irsmsx105.ger.corp.intel.com> In-Reply-To: <2601191342CEEE43887BDE71AB9772588628029A@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: e4ddd051-98a1-4a38-b20c-08d55e7f708b X-MS-Exchange-CrossTenant-originalarrivaltime: 18 Jan 2018 14:26:18.3760 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: a652971c-7d2e-4d9b-a6a4-d149256f461b X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM6PR0502MB3768 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: Thu, 18 Jan 2018 14:26:21 -0000 Hi Konstantine > Hi Matan, >=20 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > 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 > > > > > > > > correctly. > > > > > > > > > > > > > > I think if we start to protect dev->name by > > > > > > > > > > > > > > lock we need to do it for all instances (both r= ead 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 > > > > > > (by > > > > > > > > > > name or by port id). > > > > > > > > > > > It can just read it without owning it, but no managin= g 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 > > > > > > > > currently 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, > > > > > > > > release), so > > > > > > > > > > no issue here. > > > > > > > > > > > > > > > > > > > > Forget about ownership for a second. > > > > > > > > > > Suppose we have a process it created ring port for > > > > > > > > > > itself (without > > > > > > setting > > > > > > > > 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() > > > > > > > > (let > > > > > > > > > > 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? > > > > > > > > > > > > > > > > Yes. > > > > > > > > > > > > > > > > > The state are in local process memory - so process 0 > > > > > > > > > will not compare > > > > > > the > > > > > > > > process 1 port, from its point of view this port is in > > > > > > > > UNUSED > > > > > > > > > state. > > > > > > > > > > > > > > > > > > > > > > > > > Ok, and why it can't be in attached state in process 0 too? > > > > > > > > > > > > > > Someone in process 0 should attach it using protected > > > > > > > attach_secondary > > > > > > somewhere in your scenario. > > > > > > > > > > > > Yes, process 0 can have this port attached too, why not? > > > > > See the function with inline comments: > > > > > > > > > > struct rte_eth_dev * > > > > > rte_eth_dev_allocated(const char *name) { > > > > > unsigned i; > > > > > > > > > > for (i =3D 0; i < RTE_MAX_ETHPORTS; i++) { > > > > > > > > > > The below state are in local process memory, > > > > > So, if here process 1 will allocate a new port (the current > > > > > i), > > > > update its local state to ATTACHED and write the name, > > > > > the state is not visible by process 0 until someone in process > > > > 0 will attach it by rte_eth_dev_attach_secondary. > > > > > So, to use rte_eth_dev_attach_secondary process 0 must > > > > take the lock > > > > > and it can't, because it is currently locked by process 1. > > > > > > > > Ok I see. > > > > Thanks for your patience. > > > > BTW, that means that if let say process 0 will call > > > > rte_eth_dev_allocate("xxx") and process 1 will call > > > > rte_eth_dev_allocate("yyy") we can endup with same port_id be used > > > > for different devices and 2 processes will overwrite the same > > > rte_eth_dev_data[port_id]? > > > > > > No, contrary to the state, the lock itself is in shared memory, so 2 > > > processes cannot allocate port in the same time.(you can see it in > > > the next patch of this series). >=20 > I am not talking about racing here. > Let say process 0 calls rte_pmd_ring_probe()->....- > >rte_eth_dev_allocate("xxx") > rte_eth_dev_allocate() finds that port N is 'free', i.e. > local rte_eth_devices[N].state =3D=3D RTE_ETH_DEV_UNUSED so it assigns ne= w > dev ("xxx") to port N. > Then after some time process 1 calls rte_pmd_ring_probe()->....- > >rte_eth_dev_allocate("yyy"). > From its perspective port N is still free: rte_eth_devices[N].state =3D= =3D > RTE_ETH_DEV_UNUSED, so it will assign new dev ("yyy") to the same port. >=20 Yes you right, this is a problem(not related actually to port ownership) bu= t look: As I understand the secondary processes are not allowed to create a ports a= nd they must to use attach_secondary API, but there is not hardcoded check = which prevent them to do it. Konstantin >=20 >=20 > > > > > > > Actually I think only one process(primary) should allocate ports, the o= thers > should attach them. > > The race of port allocation is only between the threads of the primary > process. > > > > > > > > Konstantin > > > > > > > > > > > > > > if ((rte_eth_devices[i].state =3D=3D RTE_ETH_DEV_ATTACHED) > > > > && > > > > > strcmp(rte_eth_devices[i].data->name, name) =3D=3D 0) > > > > > return &rte_eth_devices[i]; > > > > > } > > > > > return NULL; > > > > > > > > > >