From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: "simultaneous" mounts causing weird behavior Date: Tue, 04 Nov 2003 09:02:43 -0800 Sender: autofs-bounces@linux.kernel.org Message-ID: <3FA7DBB3.1020904@zytor.com> References: <1067956957.2208.13.camel@aluminum> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1067956957.2208.13.camel@aluminum> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: autofs-bounces@linux.kernel.org Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Matthew Mitchell Cc: autofs@linux.kernel.org 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