Messages in this thread | | | From | david singleton <> | Subject | Re: PI BUG with -rt13 | Date | Fri, 18 Nov 2005 09:05:25 -0800 |
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On Nov 18, 2005, at 5:27 AM, Ingo Molnar wrote:
> > * Dinakar Guniguntala <dino@in.ibm.com> wrote: > >> Ingo, Thanks for providing the fix. However I still hit the same bug >> even with your changes > > even with my patch the robust-futex code is still quite broken. E.g. in > down_futex(), it accesses rt-mutex internals without any locking (!): > > if (rt_mutex_free(lock)) { > __down_mutex(lock __EIP__); > rt_mutex_set_owner(lock, owner_task->thread_info); > } > > both rt_mutex_free() and rt_mutex_set_owner() must be called with the > proper locking. David?
Yes, the lock needs to be protected by the robust semaphore. The locking order is:
mmap_sem to protect the vma that holds the pthread_mutex
robust_sem to protect the futex_mutex chain.
futex_mutex - the rt_mutex associated with the pthread_mutex.
This section of code performs the locking of the first waiter on the pthread_mutex, which was locked by another thread in the fast path in userspace. The fast path locking does not enter the kernel.
The first waiter locks the futex_mutex and then changes the owner to the 'owning' thread. The waiter then calls down_interruptible to block on the futex_mutex.
I'll provide a patch to protect this piece of code.
David
> > Ingo
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