Re: "Permission denied" on autofs mount point

[James Pearson <james-p@moving-picture.com>]

An update to my previous update ...

It looks like this problem is actually a server problem - I get similar
problems on SGI IRIX clients (directory access results is an 'I/O
error'). It seems to be related to one particular application writing
files to the server.

The 'servers' in question were running an old 2.4.3 kernel - upgrading
these machines to a newer kernel seems to have fixed the problem ...

James Pearson

James Pearson wrote:
> 
> An update to my previous posts:
> 
> The problem re-occurred today - from /var/log/messages on a client:
> 
> Mar 20 10:35:20 client automount[465]: attempting to mount entry
> /net/server1
> Mar 20 10:35:37 client kernel: nfs: server server1 not responding, still
> trying
> Mar 20 10:38:57 client kernel: nfs: task 62879 can't get a request slot
> Mar 20 10:39:23 client kernel: nfs: server server1 OK
> Mar 20 10:39:23 client kernel: nfs: server server1 OK
> ...
> Mar 20 10:44:23 client1 automount[21355]: expired /net/server1
> 
> Accessing /net/server1 after this time gives "Permission denied" - until
> manually umount'ing.
> 
> The machine server1 crashed or was rebooted between 10:35 and 10:39.
> 
> The client is running a RedHat 2.4.7-10 based kernel - with the
> linux-2.4.7-seekdir.dif NFS client patch and a patch to ignore server
> fsid changes across reboots.
> 
> This _seems_ to a problem with the server crashing - as other clients
> had exactly the same problem at the same time.
> 
> Would other NFS client patches improve matters?
> 
> Thanks
> 
> James Pearson
> 
> James Pearson wrote:
> >
> > Since sending my original message, I've found something on the kernel
> > list about a similar situation - see:
> >
> >  http://www.geocrawler.com/archives/3/35/2001/12/2700/7351178/
> >
> > I asked the original sender if he had any more info:
> >
> > > maybe the symptom is different, but the cause is the same, i don't know.
> > > If you write a script, that tries to unmount, you duplicate the functionality
> > > of the automounter daemon to a certain degree, what might lead to the same
> > > problems. I think the code path in fs/autofs4/root.c line 300+ is problematic:
> > >
> > >
> > >         /*
> > >          * If this dentry is unhashed, then we shouldn't honour this
> > >          * lookup even if the dentry is positive.  Returning ENOENT here
> > >          * doesn't do the right thing for all system calls, but it should
> > >          * be OK for the operations we permit from an autofs.
> > >          */
> > >         if ( dentry->d_inode && d_unhashed(dentry) )
> > >                 return ERR_PTR(-ENOENT);
> > >
> > > In my opinion it can happen that between the revalidate in 286 and this
> > > check for 'hashedness' another thread invalidates the entry and thus
> > > the syscall fails. When i find the time, i'll try to find out and fix. Possible,
> > > that it fixes also your problem, but currently i can't imagine a
> > > scenario including unavailable NFS-servers, that leads to this permission
> > > denied error.
> >
> > Could what is described be the problem?
> >
> > Is there a "fix"?
> >
> > Thanks
> >
> > James Pearson
> >
> > James Pearson wrote:
> > >
> > > I'm using autofs4 (autofs-4.0.0pre10) to mount a number of NFS mounts
> > > using a NIS map on machines running a RedHat based 2.4.7-10 kernel.
> > >
> > > Occasionally trying to access a mount point (that has been working fine)
> > > gives e.g:
> > >
> > > # cd /net/server1
> > > cd: /net/server1: Permission denied
> > >
> > > This mount point never unmounts - even with sending SIGUSR1 to automount
> > >
> > > The only way I can unmount the file system is by explicitly using umount
> > >
> > > i.e. umount /net/server1
> > >
> > > works OK and subsequent access to /net/server1 mounts the remote file
> > > system OK
> > >
> > > The remote "servers' in question tend to be other Linux workstations,
> > > that I _think_ have crashed (or been rebooted) while being mounted by
> > > the clients ...
> > >
> > > Is there anything I can do to fix this?
> > >
> > > In the meantime, I'm thinking of having a simple script that attempts to
> > > umount everything under the automount mount point every few minutes or
> > > so (by looking for these mounts in mtab) - is this likely to cause
> > > problems/confusion with automount?
> > >
> > > Thanks
> > >
> > > James Pearson
> > >
> > > _______________________________________________
> > > NFS maillist  -  NFS@lists.sourceforge.net
> > > https://lists.sourceforge.net/lists/listinfo/nfs

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