On Wed, 2008-01-30 at 11:32 +0800, wengang wang wrote:
> Thanks Ian for your reply.
>
> Ian Kent wrote:
> > On Tue, 2008-01-29 at 17:36 +0800, wengang wang wrote:
> >
> >> Hi experts,
> >>
> >> In RHEL kernel 2.6.18-53 and mainline kernel 2.6.24,
> >>
> >
> > This was a known problem due to a couple of missing patches in the
> > RHEL-5 kernel revision 53.
> >
> >
> yes.
> > I'm not aware of a problem with 2.6.24.
> >
> >
> yes, there is no problem with 2.6.24.
> By involving it, I just want to say the code
> d_instantiate(); //not d_add()
> is the same.
> >> in function autofs4_lookup() in fs/autofs4/root.c,
> >> if dentry is not found in function autofs4_lookup_unhashed(),
> >> a d_instantiate() is done on the dentry passed as parameter instead of
> >> d_add().
> >>
> >
> > d_instantiate is used to delay hashing the dentry until the following
> > mkdir as this prevents a potential deadlock.
> >
> >
> >> seems this cause a problem that the first access just after autofs
> >> started to
> >> /path/to/<autofsMountPoint>/<nfsMountPoint> fail with the error ENOENT.
> >>
> >> If I rolled back to use d_add(), there is no such problem.
> >> Is this a bug or I omitted something?
> >>
> >
> > Considering there's virtually no information to go on here I have no
> > idea but this hasn't been seen to be a problem other than in the RHEL
> > kernel above.
> >
> > You will need to provide a lot more information than this if you want me
> > to investigate.
> >
> >
> detail for this problem is:
> 1) adding a line in /etc/auto.master
> /topdir /etc/auto.topdir
> 2) in auto.topdir
> subdir -fstype=nfs hostname:/path/to/exported/directory
> 3) /etc/init.d/autofs restart
> 4) ll /topdir/subdir
> got NO SUCH DIRECTORY here.
> by strace, lstat returned ENOENT.
>
> according to your
>
> This was a known problem due to a couple of missing patches in the
> RHEL-5 kernel revision 53.
>
> I made a patch by comparing RHEL-5 53 kernel with 2.6.24. and seems it
> solves the problem.
Why, an updated kernel is available for RHEL-5 and has been for some
time. Try revision 53.1.4.
I started on getting this fixed as soon as I noticed the patches
missing.
> the patch is as below:
> ----------------------------------------------------------------------------------------------------
> --- ./fs/autofs4/root.c.orig 2008-01-29 22:20:18.000000000 -0500
> +++ ./fs/autofs4/root.c 2008-01-29 22:20:47.000000000 -0500
> @@ -662,10 +662,18 @@
> * 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)) {
> + if (!oz_mode && d_unhashed(dentry)) {
> + struct dentry *parent = dentry->d_parent;
> + struct dentry *new = d_lookup(parent, &dentry->d_name);
> + if (new != NULL)
> + dentry = new;
> + else
> + dentry = ERR_PTR(-ENOENT);
> +
> if (unhashed)
> dput(unhashed);
> - return ERR_PTR(-ENOENT);
> +
> + return dentry;
> }
>
> if (unhashed)
> ----------------------------------------------------------------------------------------------------
>
> is this patch ok and enough for RHEL-5 kernel revision 53?
Can't remember now but it's the dentry->d_inode -> !oz_mode change that
is needed for the d_add -> d_instantiate deadlock fix and yes we also
need to check if someone beat us to the mount with the d_lookup.
However, you really should use the supported updates.
Ian
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