[Xenomai] occasional EBADF in select() in notifier.c

Matthias Schneider ma30002000 at yahoo.de
Mon Apr 21 23:24:07 CEST 2014

Still working on thread suspension in forge/mercury, I occasionally get a EBADF
of the select() call in notifier.c. I suspect that this is due to accessing a 
copy of the file descriptor list notifier_rset while one of the file descriptors 
is being closed. This seems to be due to concurrent access on the notifier_rset 
from notifier_sighandler() and notifier_destroy(). "notifier_lock" is held in 
notifier_lock(), but not when copying and invoking select in notifier_sighandler().
The EBADF leads to a "spurious notification" reporting and process termination -
 obviously, the thread suspension was not triggered.

I can think of several ways of addressing this issue but I am not sure about 
side effects:
a) hold the "notifier_lock" mutex between copying the descriptor list and calling select
b) repeating the select() call in the case of EBADF

Any ideas?

Anyway, why is the select call necessary, isnt the file descriptor signaled via 
siginfo->si_fd, too?


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