[LTP] [PATCH] mem/mmapstress10: fix hangs with recent glibc

[Jan Stancek]

----- Original Message -----
> Hi!
> > There haven't been any major changes to this test in years,
> > so presumably something in recent glibc changed, that exposed
> > this problem.
> 
> I guess that it may have been elsewhere as well, such as kernel
> scheduller changes, etc.
> 
> > I confirmed with glibc-2.28, that this test can hang quite reliably
> > on 2 CPU KVM guest. It reproduces easier with smaller number of loops
> > for child_mapper() and overall test runtime reduced (-p 20 -t 0.02).
> > 
> > The problem is that childs' signal handler and main function both
> > call exit(), which can deadlock on __exit_funcs_lock:
> > 
> >   #0  0x00007f0619d72f8c in __lll_lock_wait_private () from
> >   /lib64/libc.so.6
> >   #1  0x00007f0619ca2f4b in __run_exit_handlers () from /lib64/libc.so.6
> >   #2  0x00007f0619ca3160 in exit () from /lib64/libc.so.6
> >   #3  0x00000000004039d8 in clean_mapper (sig=<optimized out>) at
> >   mmapstress10.c:898
> >   #4  <signal handler called>
> >   #5  0x00007f0619ca2fbd in __run_exit_handlers () from /lib64/libc.so.6
> >   #6  0x00007f0619ca3160 in exit () from /lib64/libc.so.6
> >   #7  0x0000000000403e7f in child_mapper (file=file@entry=0x40f530
> >   "mmapstress10.out", procno=<optimized out>,
> >       nprocs=nprocs@entry=20) at mmapstress10.c:676
> >   #8  0x0000000000403833 in main (argc=<optimized out>, argv=<optimized
> >   out>) at mmapstress10.c:458
> > 
> > Switch all signal handlers to _exit().
> 
> Looks like a reasonable band aid for the problem. I looked shortly at
> the source code and anything cleaner would require larger rewrite, so
> acked.

Pushed.

Regards,
Jan