Matthew Mitchell wrote:
Hello,

On some SMP processing nodes we have in our cluster we are noticing the
following odd behavior.  It seems like there might be a race condition
somewhere in automount that results in the same (in this case NFS)
device mounted twice on the same mountpoint.

In our case we have a (closed-source, vendor provided) data processing
app that runs 2-4 processes at a time on each of these nodes.  The
processes communicate via MPI.  What ends up happening is that each of
them tries to read data from these NFS-mounted volumes at exactly the
same time, and sometimes (about one node out of every 10) we get unlucky
and the disk gets double-mounted.

Here is the entry from the messages file where the disks are getting
mounted:
Nov  2 16:52:53 fir32 automount[674]: attempting to mount entry
/etvf/data0
Nov  2 16:52:53 fir32 automount[674]: attempting to mount entry
/etvf/data0

(Yes, there are two of them.)


This happens because mount silently changed behaviour -- autofs relies on mount only allowing one thing to be mounted on each mount point, but that was suddenly changed without warning.


-hpa

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