robust futex deadlock detection patch

[david singleton]

Here is a new patch that provides both futex deadlock detection and 
prevents ill-behaved and
malicious apps from deadlocking the kernel through the robust futex 
interface.

	http://source.mvista.com/~dsingleton/patch-2.6.15-rt2-rf1

Deadlock detection is done 'up front' for both POSIX and robust 
pthread_mutexes.   Non-recursive
POSIX mutexes will hang if deadlocked, as defined by the POSIX spec.   
The wait channel they
are hung on is 'futex_deadlock'.  This wait channel makes it easy to 
spot that your POSIX app
has deadlocked itself via the 'ps' command.

Robust futexes will have -EDEADLK returned to them since there is no 
POSIX specification for
robust mutexes,  yet, and  returning -EDEADLK is more in the spirit of 
robustness.   Robust
mutexes are cleaned up by the kernel after a thread dies and they also 
report to the app if
it is deadlocking itself.

Deadlock detection is something I have wanted to provide for both debug 
and production kernels
for a while.  It was previously available through DEBUG_DEADLOCKS.  I 
needed to add the
deadlock dection code for both production and debug kernels to prevent 
applications hanging
the kernel.

David

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