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

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

[Jan Stancek]

There haven't been any major changes to this test in years,
so presumably something in recent glibc changed, that exposed
this problem.

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().

Signed-off-by: Jan Stancek <jstancek@redhat.com>
---
 testcases/kernel/mem/mmapstress/mmapstress10.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/testcases/kernel/mem/mmapstress/mmapstress10.c b/testcases/kernel/mem/mmapstress/mmapstress10.c
index 482933bcec79..cf8403ef4b36 100644
--- a/testcases/kernel/mem/mmapstress/mmapstress10.c
+++ b/testcases/kernel/mem/mmapstress/mmapstress10.c
@@ -887,7 +887,7 @@ int fileokay(char *file, uchar_t * expbuf)
 {
 	if (!leavefile)
 		(void)unlink(filename);
-	exit(1);
+	_exit(1);
 }
 
 void clean_mapper(int sig)
@@ -895,14 +895,14 @@ void clean_mapper(int sig)
 	if (fd_mapper)
 		close(fd_mapper);
 	munmap(maddr_mapper, mapsize_mapper);
-	exit(0);
+	_exit(0);
 }
 
 void clean_writer(int sig)
 {
 	if (fd_writer)
 		close(fd_writer);
-	exit(0);
+	_exit(0);
 }
 
 unsigned int initrand(void)
-- 
1.8.3.1

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

[Cyril Hrubis]

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

[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