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From: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>
To: Matan Azrad <matan@mellanox.com>, Thomas Monjalon <thomas@monjalon.net>,
Gaetan Rivet <gaetan.rivet@6wind.com>, "Wu, Jingjing" <jingjing.wu@intel.com>
CC: "dev@dpdk.org" <dev@dpdk.org>, Neil Horman <nhorman@tuxdriver.com>,
"Richardson, Bruce" <bruce.richardson@intel.com>
Thread-Topic: [PATCH v2 2/6] ethdev: add port ownership
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Subject: Re: [dpdk-dev] [PATCH v2 2/6] ethdev: add port ownership
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Hi Matan,
>=20
> Hi Konstantin
> From: Ananyev, Konstantin, Wednesday, January 17, 2018 2:55 PM
> > >
> > >
> > > Hi Konstantin
> > > From: Ananyev, Konstantin, Sent: Wednesday, January 17, 2018 1:24 PM
> > > > Hi Matan,
> > > >
> > > > > Hi Konstantin
> > > > >
> > > > > From: Ananyev, Konstantin, Tuesday, January 16, 2018 9:11 PM
> > > > > > Hi Matan,
> > > > > >
> > > > > > >
> > > > > > > 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,
> > > > > > > <snip>
> > > > > > > > > > > > > > > > It is good to see that now scanning/updatin=
g
> > > > > > > > > > > > > > > > rte_eth_dev_data[] is lock protected, but i=
t
> > > > > > > > > > > > > > > > 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 th=
e
> > > > > > > > > > > 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_i=
d
> > > > > > > > > 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.
> > > > > >
> > > > > > Then your validation function would fail even if you'll use
> > > > > > atomic ops instead of lock.
> > > > > No.
> > > > > With atomic this specific scenario will cause the validation to p=
ass.
> > > >
> > > > Can you explain to me how?
> > > >
> > > > rte_eth_is_valid_owner_id(uint16_t owner_id) {
> > > > int32_t cur_owner_id =3D
> > > > RTE_MIN(rte_atomic32_get(next_owner_id),
> > > > UINT16_MAX);
> > > >
> > > > if (owner_id =3D=3D RTE_ETH_DEV_NO_OWNER || owner >
> > > > cur_owner_id) {
> > > > RTE_LOG(ERR, EAL, "Invalid owner_id=3D%d.\n", owner_id);
> > > > return 0;
> > > > }
> > > > return 1;
> > > > }
> > > >
> > > > Let say your next_owne_id=3D=3DX, and you invoke
> > > > rte_eth_is_valid_owner_id(owner_id=3DX+1) - it would fail.
> > >
> > > Explanation:
> > > The scenario with locks:
> > > next_owner_id =3D X.
> > > Thread 0 call to set API(with invalid owner Y=3DX) and take lock.
> >
> > Ok I see what you mean.
> > But, as I said before, if thread 0 will grab the lock first - you'll ex=
perience the
> > same failure.
> > I understand now that by some reason you treat these two scenarios as
> > something different, but for me it is pretty much the same case.
> > And to me it means that neither lock, neither atomic can fully protect =
you
> > here.
> >
>=20
> I agree that we are not fully protected even when using locks but one loc=
k are more protected than ether atomics or 2 different locks.
> So, I think keeping it as is (with one lock) makes sense.
Ok if that your preference - let's keep your current approach here.
>=20
> > > Context switch.
> > > Thread 1 call to owner_new and stuck in the lock.
> > > Context switch.
> > > Thread 0 does owner id validation and failed(Y>=3DX) - unlock the loc=
k and
> > return failure to the user.
> > > Context switch.
> > > Thread 1 take the lock and update X to X+1, then, unlock the lock.
> > > Everything is OK!
> > >
> > > The same scenario with atomics:
> > > next_owner_id =3D X.
> > > Thread 0 call to set API(with invalid owner Y=3DX) and take lock.
> > > Context switch.
> > > Thread 1 call to owner_new and change X to X+1(atomically).
> > > Context switch.
> > > Thread 0 does owner id validation and success(Y<(atomic)X+1) - unlock=
the
> > lock and return success to the user.
> > > Problem!
> > >
> > > > > With lock no next_id changes can be done while the thread is in
> > > > > the set
> > > > API.
> > > > >
> > > > > > 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:
> > > > > >
> > > > > > 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 val=
id.
> > > > > > 3) Process 0:
> > > > > > rte_eth_dev_owner_set(port_id=3D1, owner->id=3D1); It wil=
l
> > > > > > also complete 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 then same port.
> > > > > >
> > > > > > Honestly in that situation locking around nest_owner_id
> > > > > > wouldn't give you any advantages over atomic ops.
> > > > > >
> > > > >
> > > > > This is a different scenario that we can't protect on it with ato=
mic or
> > locks.
> > > > > 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 scenari=
o
> > > > > > > > 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 al=
location.
> > > > > > > > > > >
> > > > > > > > > > > > > > > > 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 l=
ock
> > > > > > > > > > > > > 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[] fi=
elds
> > > > 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 rel=
y 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 u=
se 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 ac=
cess to
> > > > > > > > > > > > > > rte_eth_dev_data[].name (which seems like a goo=
d
> > > > thing).
> > > > > > > > > > > > > > So I think any other public function that acces=
s
> > > > > > > > > > > > > > rte_eth_dev_data[].name should be protected by =
the
> > > > same
> > > > > > lock.
> > > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > > I don't think so, I can understand to use the own=
ership
> > > > > > > > > > > > > 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 nex=
t moment
> > > > > > > > > > > > > and you may get another answer) I don't see optio=
nal
> > 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 synchroniz=
ation
> > > > > > > > > > > > will be managed by ethdev."
> > > > > > > > > > > > To me it means that ethdev layer has to make sure t=
hat 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 oper=
ate
> > > > correctly.
> > > > > > > > > > I think if we start to protect dev->name by lock we nee=
d to do
> > > > > > > > > > it for all instances (both read and write).
> > > > > > > > > >
> > > > > > > > > Since under the ownership rules, the user must take owner=
ship
> > 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 u=
sing it
> > (by
> > > > > > 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 expl=
ain 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() wil=
l
> > return
> > > > > > > > rte_eth_dev * for the wrong device.
> > > > > > > Which wrong device do you mean? I guess it is the device whic=
h
> > > > 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 (with=
out
> > 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 (proce=
ss 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 com=
pare
> > 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_secondar=
y
> > somewhere in your scenario.
> >
> > Yes, process 0 can have this port attached too, why not?
> See the function with inline comments:
>=20
> struct rte_eth_dev *
> rte_eth_dev_allocated(const char *name)
> {
> unsigned i;
>=20
> for (i =3D 0; i < RTE_MAX_ETHPORTS; i++) {
>=20
> 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 a=
ttach it by rte_eth_dev_attach_secondary.
> So, to use rte_eth_dev_attach_secondary process 0 must take the lock an=
d 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("x=
xx")
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 t=
he
same rte_eth_dev_data[port_id]?
Konstantin
>=20
> 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;
>=20
>=20