[Dri-devel] module release method, threads, pids

[Keith Whitwell]

Running into a problem when killing glthreads with Ctrl-C.  Normally this 
would invoke the release() method and clean up buffers, locks etc. 
Unfortunately this doesn't work so well with threads - the release method is 
being called only once despite the 3 processes (threads) that are being 
killed.  Unfortunately the drm module makes use of current->pid extensively, 
so it really expects each thread to invoke a release() call.

As a result, killing glthreads this way almost always leaves X hung, trying to 
get the lock, waiting for a process which is already dead.

The basic scenario is like this:
--------------------------------
parent creates 2 contexts (opens one? drm fd)

parent spawns 2 threads

threads render & grab lock

--> interrupt (while lock is held by child-1)

parent/child-2 dies -- release method called
        -- pid check to release lock fails
child-1 - release method not called
        -- lock is never released
==> Actually these may be in the wrong order - perhaps the release() method is 
only called when the last thread with that fd open is killed...  The effect 
seems to be the same, though.

------------------------------------

In other words, the kernel is never being notified that the pid holding the 
lock is dying, so it never releases the lock.  This is a consequence (I think) 
of the fact that the client code opens the fd *only once*, and shares it 
between pids, the locking code is strictly based around pids but relies on the 
fd release() method for cleanup...



Partly the problem can be seen in this:

[EMAIL PROTECTED] root]# cat /proc/modules
radeon                111960   2
despite there being 3 (or 4) users of the module: X, child-1, child-2, parent.

Anyone have any ideas?

Keith



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