Re: [LTP] [PATCH] pthread_detach: avoid threads sharing stack

[Wanlong G. <gao...@cn...>]

Hi Kang,

> 
> This testcase was observed to crash with segmentation fault:
> http://www.mail-archive.com/ltp...@li.../msg14692.html

Have you tested this patch from Jan on your system?

Thanks,
Wanlong Gao

> 
> Following issues have been found:
> - When detached thread signals it's done, it's not really done yet
>   and it is possible for scheduler to switch to test() thread and create
>   another thread(s) that uses same altstack. sem_post/sem_wait
>   is not reliable way to tell when detached thread is finished.
>   test() thread can continue to spawn new threads and unprivileged user
>   can run out of resources.
> - Threads which fire SIGUSR signals can do so very frequently,
>   so threaded() thread may not progress at all and it starts to
>   progress only when signal threads are told to stop sending signals.
> 
> This patch modifies testcase in following way:
> 
> Before
> -------
> test() loops over all scenarios repeatedly and spawns new threaded()
> as soon as previous one called sem_post.
> 
> main +
>      |\
>      | send_sig1 (thread)
>      |\
>      | send_sig2 (thread)
>      \
>        test (thread)
>          \
>           threaded (detached thread)
> 
> After
> ------
> Only one thread is sending signals (SIGUSR1) with gradually increasing
> sleep time to make sure threaded() can progress. test() loops over
> scenarios just once.
> 
> main() loops for specified time, it spawns new child and waits for it
> to finish. This will avoid using same stack by 2+ threads and there will be
> no more than NSCENAR threads at a time.
> 
> main (procA)
>              \
>               do_child (procB) +
>                                |\
>                                | send_sig (thread)
>                                 \
>                                  test (thread)
>                                    \
>                                     threaded (detached thread)
> 
> Modified version have been succesfully tested by reporter:
> routerstation(mips), x86_64(ubuntu11.10 & redhat 5.3)
> and x86(redhat 5.3) each 100+ times
> 
> and by me: 100+ times as root and unprivileged user on:
> RHEL5.8 (i386, x86_64, ia64, ppc64, s390x)
> RHEL6.0 (i386, x86_64, ppc64, s390x)
> RHEL6.3 (i386, x86_64, ppc64, s390x)
> 
> Following glibc bug has been observed during testing on ppc64:
> Bug 852445 - gcc_assert failure in _Unwind_SetSpColumn() on ppc64
> https://bugzilla.redhat.com/show_bug.cgi?id=852445
> 
> This patch is currently not making any workarounds to avoid
> hitting this issue, because so far it is known to happen only
> rarely on ppc64 when unprivileged user runs the testcase.
> If this issue becomes more significant, testcase can be modified
> to skip scenarios with explicit scheduling if they are run by
> unprivileged user.
> 
> Reported-by: Kang Kai <kai...@wi...>
> Signed-off-by: Jan Stancek <jst...@re...>
> ---
>  .../conformance/interfaces/pthread_detach/4-3.c    |  239 ++++++++++++--------
>  1 files changed, 142 insertions(+), 97 deletions(-)
> 
> 
> 
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