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

["De Lara Guarch, Pablo" <pablo.de.lara.guarch@intel.com>]

Hi Dhana,

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Dhananjaya Reddy
> Eadala
> Sent: Wednesday, March 02, 2016 2:02 PM
> To: Qiu, Michael
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] hash: fix memcmp function pointer in multi-
> process
> 
> Michael
> 
> Please find the attached is the patch file generated from "git format-patch
> -1"

What Michael means is that you should use git send-email and not attach the patch
to the mail.

You can use:

git send-email -1 --to dev@dpdk.org

or

git send-email your-patch.patch --to dev@dpdk.org

Take a look at dpdk.org/dev for more details and how to configure git with your smtp server details.

Thanks,
Pablo

> 
> 
> 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
> > >
> >
> >