Re: [PATCH 1/2] drivers/mempool: add stack mempool handler as driver

[Olivier Matz <olivier.matz@6wind.com>]

On Tue, 28 Mar 2017 17:12:47 +0530, Shreyansh Jain <shreyansh.jain@nxp.com> wrote:
> Hello Olivier,
> 
> On Friday 24 March 2017 09:52 PM, Olivier Matz wrote:
> [..]
> 
> > I tried to pass the mempool autotest, and it issues a segfault.
> > I think the libraries are missing in rte.app.mk, so no handler is
> > registered.  
> 
> I have been trying to simulate the segfault that you are referring to 
> above. But, I think it should not be the case. If a mempool handler is 
> not registered (as librte_mempool_ring was not included in 
> mk/rte.app.mk, so, no "ring_mp_mc"), the caller would get error.
> 
> The mempool_autotest is reporting:
> 
> --->8--  
> RTE>>mempool_autotest  
> cannot allocate mp_nocache mempool
> Test Failed
> --->8--  

Here are the reproduction steps:


git clone http://dpdk.org/git/dpdk
cd dpdk/
wget -O - http://dpdk.org/dev/patchwork/patch/21986/mbox | git am -
wget -O - http://dpdk.org/dev/patchwork/patch/21985/mbox | git am -
make config T=x86_64-native-linuxapp-gcc
make -j32 test-build
echo 128 > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages
mkdir -p /mnt/huge
mount -t hugetlbfs none /mnt/huge
echo mempool_autotest | ./build/app/test --
# segfault

# replay with debug
make -j32 test-build
make -j32 EXTRA_CFLAGS="-O0 -g" test-build
ulimit -c unlimited
echo mempool_autotest | ./build/app/test --
# segfault + core dump
gdb -c core ./build/app/test

(gdb) bt
#1  0x000000000064dead in rte_mempool_ops_alloc (mp=0x7f8816abdb40)
    at /root/dpdk/lib/librte_mempool/rte_mempool_ops.c:101
#2  0x000000000064c1e7 in rte_mempool_populate_phys (mp=0x7f8816abdb40, 
    vaddr=0x7f880987a800 <error: Cannot access memory at address 0x7f880987a800>, 
    paddr=6958852096, len=26761152, free_cb=0x64c032 <rte_mempool_memchunk_mz_free>, 
    opaque=0x7f8822334d4c) at /root/dpdk/lib/librte_mempool/rte_mempool.c:359
#3  0x000000000064c9db in rte_mempool_populate_default (mp=0x7f8816abdb40)
    at /root/dpdk/lib/librte_mempool/rte_mempool.c:572
#4  0x000000000064d3d4 in rte_mempool_create (name=0x9b1ff0 "test_nocache", n=12671, 
    elt_size=2048, cache_size=0, private_data_size=0, mp_init=0x0, mp_init_arg=0x0, 
    obj_init=0x49f309 <my_obj_init>, obj_init_arg=0x0, socket_id=-1, flags=0)
    at /root/dpdk/lib/librte_mempool/rte_mempool.c:895
#5  0x00000000004a20ed in test_mempool () at /root/dpdk/test/test/test_mempool.c:519
#6  0x0000000000435189 in cmd_autotest_parsed (parsed_result=0x7ffe55006420, 
    cl=0x7c87090, data=0x0) at /root/dpdk/test/test/commands.c:103
#7  0x00000000006749df in cmdline_parse (cl=0x7c87090, 
    buf=0x7c870d8 "mempool_autotest\n")
    at /root/dpdk/lib/librte_cmdline/cmdline_parse.c:359
(gdb) up
#1  0x000000000064dead in rte_mempool_ops_alloc (mp=0x7f8816abdb40)
    at /root/dpdk/lib/librte_mempool/rte_mempool_ops.c:101
101             return ops->alloc(mp);
(gdb) print ops
$1 = (struct rte_mempool_ops *) 0x4e69c00 <rte_mempool_ops_table+64>
(gdb) print *ops
$2 = {name = '\000' <repeats 31 times>, alloc = 0x0, free = 0x0, enqueue = 0x0, 
  dequeue = 0x0, get_count = 0x0}


Regards,
Olivier


> 
> >
> > Adding the following code in lib/librte_mempool/rte_mempool_ops.c
> > fixes the crash.
> >
> >         ops = rte_mempool_get_ops(mp->ops_index);
> > +       if (ops == NULL || ops->alloc == NULL)
> > +               return -ENOTSUP;
> >         return ops->alloc(mp);  
> 
> Can you tell me for which case did your code reach 
> rte_mempool_ops_alloc() and segfault?
> 
> In my case, librte_mempool_ring and librte_mempool_stack are not added 
> to mk/rte.app.mk and it is static compilation.
> 
> >
> > Now that drivers are not linked to the mempool library, it can
> > happen that there is no handler. Could you please add this patch in your
> > patchset?  
> 
> Yes, once I can get this issue reproduced. Because I think there is one 
> more place similar code should go (rte_mempool_ops_getcount).
> As per what I can see, this would only happen if rte_mempool_xmem_create 
> is called and then directly alloc is called. That is not happening for 
> mempool_autotest.
> 
> -
> Shreyansh
>