Re: [dpdk-dev] [PATCH] hash: fix memcmp function pointer in multi-process

[Dhananjaya Reddy Eadala <edreddy@gmail.com>]

Michael

Please find the attached is the patch file generated from "git format-patch
-1"


Thanks
Dhana


On Tue, Mar 1, 2016 at 9:29 PM, Qiu, Michael <michael.qiu@intel.com> wrote:

> On 3/2/2016 2:57 AM, Dhananjaya Reddy Eadala wrote:
> > Hi
> >
> > We found a problem in dpdk-2.2 using under multi-process environment.
> > Here is the brief description how we are using the dpdk:
> >
> > We have two processes proc1, proc2 using dpdk. These proc1 and proc2 are
> > two different compiled binaries.
> > proc1 is started as primary process and proc2 as secondary process.
> >
> > proc1:
> > Calls srcHash = rte_hash_create("src_hash_name") to create rte_hash
> > structure.
> > As part of this, this api initalized the rte_hash structure and set the
> > srcHash->rte_hash_cmp_eq to the address of memcmp() from proc1 address
> > space.
> >
> > proc2:
> > calls srcHash =  rte_hash_find_existing("src_hash_name"). This returns
> the
> > rte_hash created by proc1.
> > This srcHash->rte_hash_cmp_eq still points to the address of memcmp()
> from
> > proc1 address space.
> > Later proc2  calls rte_hash_lookup_with_hash(srcHash, (const void*) &key,
> > key.sig);
> > Under the hood, rte_hash_lookup_with_hash() invokes
> > __rte_hash_lookup_with_hash(), which in turn calls
> h->rte_hash_cmp_eq(key,
> > k->key, h->key_len).
> > This leads to a crash as h->rte_hash_cmp_eq is an address from proc1
> > address space and is invalid address in proc2 address space.
> >
> > We found, from dpdk documentation, that
> > "
> >  The use of function pointers between multiple processes running based of
> > different compiled
> >  binaries is not supported, since the location of a given function in one
> > process may be different to
> >  its location in a second. This prevents the librte_hash library from
> > behaving properly as in a  multi-
> >  threaded instance, since it uses a pointer to the hash function
> internally.
> >
> >
> >  To work around this issue, it is recommended that multi-process
> > applications perform the hash
> >  calculations by directly calling the hashing function from the code and
> > then using the
> >  rte_hash_add_with_hash()/rte_hash_lookup_with_hash() functions instead
> of
> > the functions which do
> >  the hashing internally, such as rte_hash_add()/rte_hash_lookup().
> > "
> >
> > We did follow the recommended steps by invoking
> rte_hash_lookup_with_hash().
> > It was no issue up to and including dpdk-2.0. In later releases started
> > crashing because rte_hash_cmp_eq is introduced in dpdk-2.1
> >
> > We fixed it with the following patch and would like to submit the patch
> to
> > dpdk.org.
>
> Could you send the patch in the mail?
>
> Learn how to send a patch:
>
> http://www.dpdk.org/dev
>
> Thanks,
> Michael
> > Patch is created such that, if anyone wanted to use dpdk in multi-process
> > environment with function pointers not shared, they need to
> > define RTE_LIB_MP_NO_FUNC_PTR in their Makefile. Without defining this
> flag
> > in Makefile, it works as it is now.
> >
> >
> > Please find here attached is the patch file.
> >
> > Thanks
> > Dhana
> >
>
>