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

[Cyril Hrubis <chrubis@suse.cz>]

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.

-- 
Cyril Hrubis
chrubis@suse.cz