re: nfsd: skip some unnecessary stats in the v4 case

[Colin Ian King <colin.king@canonical.com>]

Hi,

Static analysis on today's linux-next has found an issue with the
following commit:

commit 55ea6691d52875b921d3712f9a08db8e81e059b4
Author: J. Bruce Fields <bfields@redhat.com>
Date:   Fri Nov 20 17:39:19 2020 -0500

    nfsd: skip some unnecessary stats in the v4 case


The analysis is as follows:

286 /*
287  * Fill in the post_op attr for the wcc data
288  */
289 void fill_post_wcc(struct svc_fh *fhp)
290 {
291        bool v4 = (fhp->fh_maxsize == NFS4_FHSIZE);
292        struct inode *inode = d_inode(fhp->fh_dentry);

   1. var_decl: Declaring variable err without initializer.

293        __be32 err;
294

   2. Condition fhp->fh_post_saved, taking true branch.

295        if (fhp->fh_post_saved)
296                printk("nfsd: inode locked twice during operation.\n");
297
298

   3. Condition !v4, taking false branch.
   4. Condition !inode->i_sb->s_export_op->fetch_iversion, taking false
branch.

299        if (!v4 || !inode->i_sb->s_export_op->fetch_iversion)
300                err = fh_getattr(fhp, &fhp->fh_post_attr);

   5. Condition v4, taking true branch.

301        if (v4)
302                fhp->fh_post_change =
303                        nfsd4_change_attribute(&fhp->fh_post_attr,
inode);

Uninitialized scalar variable (UNINIT)6. uninit_use: Using uninitialized
value err.

304        if (err) {
305                fhp->fh_post_saved = false;
306                /* Grab the ctime anyway - set_change_info might use
it */
307                fhp->fh_post_attr.ctime = inode->i_ctime;
308        } else
309                fhp->fh_post_saved = true;
310 }

Prior to this commit, variable err used to be always assigned by the
call to err = fh_getattr(fhp, &stat), but now it is only called on
specific conditions, so now we have this unassigned err issue.

Colin