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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