[ python-Bugs-1069160 ] PyThreadState_SetAsyncExc segfault

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Bugs item #1069160, was opened at 2004-11-18 20:48
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Category: Python Interpreter Core
Group: Python 2.4
Status: Open
Resolution: None
Priority: 6
Submitted By: Tim Peters (tim_one)
Assigned to: Nobody/Anonymous (nobody)
Summary: PyThreadState_SetAsyncExc segfault

Initial Comment:
PyThreadState_SetAsyncExc() crawls over the list of 
tstates without holding a mutex.  Python implementation 
code has tried to get away with this kind of thing before 
(& more than once <wink>:  and segfaults are always 
eventually reported.

A common cause is that PyThreadState_DeleteCurrent() 
is typically called *without* the GIL held, so any thread 
can try to delete its own tstate *while* 
PyThreadState_SetAsyncExc() is trying to muck with 
that tstate.  That the GIL is held by 
PyThreadState_SetAsyncExc's caller is no protection.  
Instead the code has to serialize against tstate chain 
mutations by acquiring head_mutex for the duration.

Of course this is rare and can be virtually impossible to 
reproduce, but that makes the bug worse, not "better".





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