Red Hat Bugzilla – Bug 873286
race condition : master pty used in mom_reader()/mom_writer() alternates blocking and non blocking state
Last modified: 2013-02-13 10:32:25 EST
I noticed that the file descriptor of the master pty shared by parent and child pbs_mom processes alternates between blocking and non blocking state.
The consequence of this race condition is that read() from mom_writer() sometimes fails, and returns -1, with errno=EAGAIN (which is the expected behaviour when the related file descriptor is not blocking, but this is not expected by the code of mom_writer()), causing the submitted task to terminate unexpectedly.
The problem is caused because the corresponding mom_reader() function, from the other process calls write() on this same pty, this function is #defined to write_nonblocking_socket(), and this function temporally change the state of the pty from blocking to non_blocking.
I experience this problem systematically in a VM running Fedora 16 x86_64, when submitting interactive jobs. REproducing this case on real hardware (same distro, same packages) is much more difficult.
A possible fix would be to gracefully handle the EAGAIN errno in the mom_writer() loop.
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