Re: autofs4 looks up wrong path element when ghosting is enabled

[Jeff Moyer <jmoyer@redhat.com>]

==> Regarding Re: autofs4 looks up wrong path element when ghosting is enabled; Ian Kent <raven@themaw.net> adds:

raven> On Thu, 22 Sep 2005, Jeff Moyer wrote:
>> ==> Regarding Re: autofs4 looks up wrong path element when ghosting is
>> enabled; Ian Kent <raven@themaw.net> adds:
>> 
raven> On Tue, 20 Sep 2005, Jeff Moyer wrote:
>> >> Hi, Ian, list,
>> >> 
>> >> I have a bug filed against autofs when ghosting is enabled.  The best
>> way >> to describe the bug is to walk through the reproducer, I guess.
>> >> 
>> >> Take the following maps, for example:
>> >> 
>> >> auto.master >> /sbox auto.sbox
>> >> 
>> >> auto.sbox: >> src segfault:/sbox/src/
>> >> 
>> >> Let's say that there is a file, id3_0.12.orig.tar.gz, in
>> segfault:/sbox/src/.
>> >> 
>> >> To reproduce the problem, stop the nfs service on the server.
>> >> 
>> >> On the client, do an 'ls /sbox/src/id3_012.orig.tar.gz'.  This will
>> fail, >> as well it should.  However, if we look in the logs, we find
>> this:
>> >> 
>> >> automount[1182]: handle_packet_missing: token 1, name src >>
>> automount[1182]: attempting to mount entry /sbox/src >> ...  >>
>> automount[1481]: mount(nfs): calling mkdir_path /sbox/src >>
>> automount[1481]: mount(nfs): calling mount -t nfs -s-o
>> tcp,intr,timeo=600,rsize=8192,wsize=8192,retrans=5 segfault:/sbox/src
>> /sbox/src >> automount[1481]: >> mount: RPC: Program not registered >>
>> automount[1481]: mount(nfs): add_bad_host: segfault:/sbox/src >>
>> automount[1481]: mount(nfs): nfs: mount failure segfault:/sbox/src on
>> /sbox/src >> automount[1481]: failed to mount /sbox/src >> ...  >>
>> automount[1182]: send_fail: token=1 >> automount[1182]: handle_packet:
>> type = 0 >> automount[1182]: handle_packet_missing: token 2, name
>> src/id3_0.12.orig.tar.gz >> automount[1182]: attempting to mount entry
>> /sbox/src/id3_0.12.orig.tar.gz
>> >> 
>> >> Noteworthy are these last two lines!  Even though the mount failed,
>> we are >> continuing the lookup.  The culprit is here, in cached_lookup:
>> >> 
>> >> if (!dentry->d_op->d_revalidate(dentry, flags) &&
>> !d_invalidate(dentry)) { >> dput(dentry); >> dentry = NULL; >> }
>> >> 
>> >> d_revalidate points to autofs4_revalidate, which calls
>> try_to_fill_dentry, >> which will return a status of 0.  Since ghosting
>> is enabled, >> d_invalidate(dentry) will return -EBUSY, and so we return
>> the dentry to
raven> the
>> >> caller, which then continues the lookup.
>> >> 
>> >> Ian, I'm not really sure how we can address this issue without VFS >>
>> changes.  Any ideas?
>> >> 
>> 
raven> I'm aware of this problem.  I'm not sure how to deal with it yet.
raven> The case above is probably not that difficult to solve but if the
raven> last component is a directory it's hard to work out it's a problem.
>> Ugh.  If you're thinking what I think you're thinking, that's an ugly
>> hack.

raven> Don't think so.

raven> I've been seeing this for a while. I wasn't quite sure of the source
raven> but, for some reason your report has cleared that up.

raven> The problem is not so much the success returned on the failed mount
raven> (revalidate). It's the return from the following lookup. This is a
raven> lookup in a non-root directory. I replaced the non-root lookup with
raven> the root lookup a while ago and I think this is an unexpected side
raven> affect of that. Becuase of other changes that lead to that decision
raven> I think that it should be now be OK to put back the null function
raven> (always return a negative dentry) that was there before I started
raven> working on the browable maps feature.

raven> I'll change the module I use here and test it out for a while.  If
raven> you have time I could make a patch for the 2.4 code and send it over
raven> so that you could test it out a bit as well.

Just send along the 2.6 patch, since I have to deal with that, too.  I'll
go through the trouble of backporting it.

>>
raven> There's more information here than I've gathhered so far.
>> >> Oh, also note that, once the nfs service is started up again on the
>> server, >> the lookup of a specific file name will still fail!  In this
>> case, the >> daemon won't even be called.
>> 
raven> I'll have to check this out.  It could be helpful.
>> Well, I've provided a reproducer.  If you'd like log output from the
>> kernel side, let me know.  I can certainly provide that.

raven> Don't think I need it.  I'm fairly sure I understand what's
raven> happening here now. As I said above.

Cool.  Thanks!

Jeff
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