Re: [dpdk-dev] [PATCH] eal: fix threads block on barrier

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 27 Apr 2018 17:36:56 +0000
Shreyansh Jain <shreyansh.jain@nxp.com> wrote:

> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Jianfeng Tan
> > Sent: Friday, April 27, 2018 10:12 PM
> > To: dev@dpdk.org
> > Cc: thomas@monjalon.net; Jianfeng Tan <jianfeng.tan@intel.com>; Olivier
> > Matz <olivier.matz@6wind.com>; Anatoly Burakov
> > <anatoly.burakov@intel.com>
> > Subject: [dpdk-dev] [PATCH] eal: fix threads block on barrier
> > 
> > Below commit introduced pthread barrier for synchronization.
> > But two IPC threads block on the barrier, and never wake up.
> > 
> >   (gdb) bt
> >   #0  futex_wait (private=0, expected=0, futex_word=0x7fffffffcff4)
> >       at ../sysdeps/unix/sysv/linux/futex-internal.h:61
> >   #1  futex_wait_simple (private=0, expected=0,
> > futex_word=0x7fffffffcff4)
> >       at ../sysdeps/nptl/futex-internal.h:135
> >   #2  __pthread_barrier_wait (barrier=0x7fffffffcff0) at
> > pthread_barrier_wait.c:184
> >   #3  rte_thread_init (arg=0x7fffffffcfe0)
> >       at ../dpdk/lib/librte_eal/common/eal_common_thread.c:160
> >   #4  start_thread (arg=0x7ffff6ecf700) at pthread_create.c:333
> >   #5  clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
> > 
> > Through analysis, we find the barrier defined on the stack could be the
> > root cause. This patch will change to use heap memory as the barrier.
> > 
> > Fixes: d651ee4919cd ("eal: set affinity for control threads")
> > 
> > Cc: Olivier Matz <olivier.matz@6wind.com>
> > Cc: Anatoly Burakov <anatoly.burakov@intel.com>
> > 
> > Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>  
> 
> Though I have seen Stephen's comment on this (possibly a library bug), this at least fixes an issue which was dogging dpaa and dpaa2 - generating bus errors and futex errors with variation in core masks provided to applications.
> 
> Thanks a lot for this.
> 
> Acked-by: Shreyansh Jain <shreyansh.jain@nxp.com>

Could you verify there is not a use after free by using valgrind or some library that poisons memory on free.