Messages in this thread | | | Date | Thu, 28 Oct 2004 19:21:22 +0200 | From | Manfred Spraul <> | Subject | Re: Livelock with the shmctl04 test program from linux test project |
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Alexander Nyberg wrote:
>Sorry for late reply, but I just can't understand why & how this happens, been trying to grasp >the IPC/SHM part but I'm missing something. One processor gets locked up and never released. > > Ok - that's a deadlock.
>I did: > >printk("taking lock\n"); >spin_lock(&info->lock); >printk("lock taken\n"); > >and it never prints out "lock taken" so i know where it locks up. Now the fun part, >spinlock debugging doesn't catch it, > That's not surprising: the full debug code is only active for uniprocessor kernels. On SMP, only a simple check for unitialized spinlocks is performed. Btw, I'd use printk("thread %d, struct %p: taking lock", current->pid, info); Then you are certain that you are not fooled by multiple concurrent operations.
> but I did a simple patch to show who is holding a lock >at the current time, and it appears noone has taken the lock. I really don't get this. > > > I must think about it. Who's printed as the last owner that released the lock? Perhaps there is a race with segment destruction: The structures are protected by RCU.
Could you enable debug spinlocks and slab debugging? I would have expected an error message from spinlock debugging due to bad magic.
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