Bug 873286 - race condition : master pty used in mom_reader()/mom_writer() alternates blocking and non blocking state
race condition : master pty used in mom_reader()/mom_writer() alternates bloc...
Product: Fedora
Classification: Fedora
Component: torque (Show other bugs)
Unspecified Unspecified
unspecified Severity unspecified
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Assigned To: Haïkel Guémar
Fedora Extras Quality Assurance
Depends On:
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Reported: 2012-11-05 08:50 EST by Fabrice Bellet
Modified: 2013-02-13 10:32 EST (History)
2 users (show)

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Doc Type: Bug Fix
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Last Closed: 2013-02-13 10:32:22 EST
Type: Bug
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Description Fabrice Bellet 2012-11-05 08:50:58 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.
Comment 1 Fedora End Of Life 2013-01-16 09:28:45 EST
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Comment 2 Fedora End Of Life 2013-02-13 10:32:25 EST
Fedora 16 changed to end-of-life (EOL) status on 2013-02-12. Fedora 16 is 
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