On Thu, 2010-12-23 at 15:08 -0500, Fred Isaman wrote:
> On Dec 23, 2010, at 2:25 PM, Trond Myklebust wrote:
>
> > On Thu, 2010-12-23 at 12:29 -0500, Fred Isaman wrote:
> >> +
> >> + if (args->cbl_recall_type == RETURN_FILE) {
> >> + LIST_HEAD(free_me_list);
> >> +
> >> + args->cbl_inode = NULL;
> >> + spin_lock(&clp->cl_lock);
> >> + list_for_each_entry(lo, &clp->cl_layouts, plh_layouts) {
> >> + if (nfs_compare_fh(&args->cbl_fh,
> >> + &NFS_I(lo->plh_inode)->fh))
> >> + continue;
> >> + if (test_bit(NFS_LAYOUT_BULK_RECALL, &lo->plh_flags))
> >> + rv = NFS4ERR_DELAY;
> >> + else {
> >> + /* Without this, layout can be freed as soon
> >> + * as we release cl_lock. Matched in
> >> + * do_callback_layoutrecall.
> >> + */
> >> + get_layout_hdr(lo);
> >> + args->cbl_inode = lo->plh_inode;
> >> + rv = NFS4_OK;
> >> + }
> >> + break;
> >> + }
> >> + spin_unlock(&clp->cl_lock);
> >> +
> >> + spin_lock(&lo->plh_inode->i_lock);
> >
> > What guarantees do you have that the inode still exists here? Does the
> > layout segment hold a reference to it?
> >
>
> This section is why I once asked about whether the layout needs to reference the inode. I believe the answer is nothing. The lseg/layout definitely does not hold direct references. I assume doing grab/put of inode here and below is acceptable?
igrab/iput is fine in this context.
There is also the question: what if we don't find a match for the layout
recall arguments? It looks to me as if we end up with 'lo ==
clp->cl_layouts', with disastrous consequences when we then do
spin_lock(lo->plh_inode->i_lock)...
> > Also, How do you know that (!test_bit(NFS_LAYOUT_BULK_RECALL,
> > &lo->plh_flags)) is still valid when you get here?
> >
>
> Because it can not be set elsewhere while the NFS4CLNT_LAYOUTRECALL bit is set.
OK. One race averted :-)
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
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