> From: Gary Funck
> Sent: Saturday, July 15, 2006 10:07 AM
>
> A test program which allocates about 256M of MAP_ANONYMOUS mmap memory,
> and then spawns 4 processess, where each process i writes to 1/4 of the
> mapped memory, and then reads the memory written by
> the process (i + 1)%4, triggers a soft lockup, when exiting.
> Hardware:
> dual core dual Opteron 275 (Tyan motherboard, 4G physical memory)
> has been rock solid reliable.
>
> BUG: soft lockup detected on CPU#3!

Follow up, the attached test program, when compiled on FC5 with the
2.6.17-1.2145 kernel will cause lost timer ticks, lost RS-232 interrupts,
and often will lead to the soft lockup situation shown below:

BUG: soft lockup detected on CPU#0!

Call Trace: <IRQ> <ffffffff802b2fb5>{softlockup_tick+219}
       <ffffffff8029708e>{update_process_times+66}
<ffffffff8027a3ed>{smp_local_timer_interrupt+35}
       <ffffffff8027aa95>{smp_apic_timer_interrupt+65}
<ffffffff80263acb>{apic_timer_interrupt+135} <EOI>
       <ffffffff8020e578>{__set_page_dirty_nobuffers+0}
<ffffffff8020a7ab>{release_pages+111}
       <ffffffff80267b76>{thread_return+0}
<ffffffff80267bd4>{thread_return+94}
       <ffffffff8020e578>{__set_page_dirty_nobuffers+0}
<ffffffff8020e578>{__set_page_dirty_nobuffers+0}
       <ffffffff8020e09e>{free_pages_and_swap_cache+115}
<ffffffff80207b62>{unmap_vmas+1145}
       <ffffffff8023c7d9>{exit_mmap+120} <ffffffff8023eda8>{mmput+44}
       <ffffffff80215ece>{do_exit+599}
<ffffffff8024cacd>{debug_mutex_init+0}
       <ffffffff80262f01>{tracesys+209}

After compiling the code, A continuous loop like the following, seems to
eventually lead to the soft lockup situation (FC5, x86_64) shown above:

while true; do
  a.out
done