Re: Near-simultaneous automount of multiple directories fails

[Ian Kent <raven@themaw.net>]

On Fri, 2016-04-08 at 09:55 +0200, Marcel De Boer wrote:
> Hi!
> 
> I've already reported this on the CentOS bug tracker a while ago, but
> I 
> thought I'd report it here too.
> 
> https://bugs.centos.org/view.php?id=9835
> 
> Summarized (there's more information on the bug report): on one of our
> servers we initially saw that every few days one home directory became
> inaccessible. This happened to two different homedirectories (but only
> one 
> at a time) out of the couple hundred we have. We traced this to 
> simultaneously scheduled cron scripts running out of the affected 
> homedirectories, which caused both directories to be mounted nearly 
> simultaneously.
> 
> A test setup on a different machine (the primary description from the
> bug 
> report, as the server was not stock CentOS) also showed that if we had
> cron simultaneously mount four directories every 10 minutes, only half
> of 
> them would get mounted every time. On this machine an RPM rebuild of 
> autofs made the issue disappear, but it was much more persistent on
> the 
> server.
> 
> Eventually it seems that there is an issue in mount_mount() from 
> mount_nfs.c; to my untrained eye, it looks like it can get called 
> simultaneously from different threads, where they change shared 
> information, probably the 'hosts' or 'tmp' lists.

Whatever the problem is it isn't access to either of these two variables
or the lists they may represent.

They are both local variables of the mount_mount() function and so
cannot be accessed simultaneously by any other function.

Ian
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